Effects of preterm birth and bronchopulmonary dysplasia on infants’ pulmonary function: A cohort study of 117 infants

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This study explores pulmonary function impairment in preterm infants using plethysmography and examines its correlation with bronchopulmonary dysplasia. Methods One hundred and seventeen infants were divided into preterm and term groups, including 57 preterm infants and 60 term infants. Preterm infants were divided into bronchopulmonary dysplasia (BPD) and non-BPD groups. There were 22 cases in the BPD group and 35 cases in the non-BPD group. Preterm infants were further divided into a < 34 weeks group and a 34 ~ 36 + 6 weeks group according to gestational age. There were 26 cases in the < 34 weeks group and 31 cases in the 34 ~ 36 + 6 weeks group. The pulmonary function of each group was measured by plethysmography when the age of the infant was < 6 months. Results Compared with the term group, the preterm group had a significantly higher cesarean section rate and faster respiratory rate (RR) and lower values of the ratio of time to peak tidal expiratory flow to total expiratory time (TPEF/tE), the ratio of volume to peak tidal expiratory flow to total expiratory volume (VPEF/VE), compliance of the respiratory system (Crs), and plethysmographic functional residual capacity (FRCp). Comparisons among infants of different gestational ages revealed statistically significant differences in RR, TPEF/tE, respiratory resistance, VPEF/VE, and FRCp. Comparisons among the three groups of BPD group, non-BPD group, and term group revealed differences in RR, TPEF/tE, VPEF/VE, Crs, and FRCp that were statistically significant. Conclusions There is a certain degree of pulmonary function impairment in preterm infants, which is more severe in early preterm infants, and in preterm infants with BPD than in preterm infants without BPD. Plethysmography is helpful in the early assessment of pulmonary function in preterm infants. preterm infants pulmonary function bronchopulmonary dysplasia 1. Background With the progress of medicine, the survival rate of very preterm infants has been increasing year by year due to the use of antenatal steroids, the improvement of post-natal resuscitation strategies and primary respiratory support, the improvement of nursing care, and the use of post-natal surfactant. However, the incidence of preterm birth is still increasing, and the harms associated with preterm birth still need to be addressed [ 1 ] . The most significant consequences of premature birth are pulmonary damage and neurological impairment. Research has revealed that even in the absence of prolonged mechanical ventilation and oxygen therapy postpartum, preterm birth exerts an adverse influence on lung development [ 2 ] , and pulmonary damage in the neonatal period may have a long-term effect on the respiratory system [ 2 – 4 ] . In recent years, there have been many studies about pulmonary function as a method for evaluating pulmonary function damage. Most of these studies focus on pulmonary function in school-aged children; however, there are many factors that cause changes in pulmonary function during growth and development from birth through childhood. However, there are only a few studies on pulmonary function in infants, and the results are not consistent [ 5 – 8 ] . Plethysmography is a technically demanding method to detect pulmonary function. It is a non-invasive method to obtain information about lung volume and airway obstruction that cannot be obtained by spirometry [ 9 ] . The aim of this study was to investigate whether pulmonary function is impaired in preterm infants and whether the degree of pulmonary function impairment is related to the occurrence of bronchopulmonary dysplasia. 2. Methods A total of 117 infants hospitalized in the respiratory department of Chengdu Women’s and Children's Central Hospital between January 2021 and June 2022 were included in this study. The infants were followed up in the respiratory department one month after discharge with an age of less than 6 months as study participants, including 57 cases in the preterm group and 60 cases in the term group. Preterm infants were divided into the bronchopulmonary dysplasia (BPD) group and the non-BPD group, with 22 cases in the BPD group and 35 cases in the non-BPD group. The diagnosis of BPD was in accordance with the 2019 Jensen Criteria [ 10 ] . BPD was diagnosed when the infant was at 36 weeks’ postmenstrual age or when the infant was discharged with respiratory support. Preterm infants were divided into the < 34 weeks group (26 cases) and the 34 ~ 36 + 6 weeks group (31 cases) according to gestational age. Exclusion criteria included: (1) infants with symptoms of respiratory infection at the time of pulmonary function testing; (2) serious congenital heart diseases, central nervous system respiratory regulation abnormalities, congenital diaphragmatic hernia, and other myeloid deformities that may affect pulmonary function; (3) test results that did not meet quality control criteria (coefficient of variation of tidal volume or functional residual air volume > 10%, and children who did not complete pulmonary function tests); and (4) incomplete data, loss of follow-up, and adverse outcomes. Clinical data collection: (1) production condition, including delivery, birth length, birth weight, and gestational age; and (2) general condition during hospitalization including gender, length, weight, age in months, presence of wheezing, white blood cell (WBC) count, and eosinophil (EOS) count. Infant plethysmography was used to measure pulmonary function in all participants in accordance with the American Thoracic Society/European Respiratory Association guidelines for infant pulmonary function testing [ 11 , 12 ] . Before the test, the instrument was calibrated for ambient temperature, atmospheric pressure, and volume. Before the test, oral and nasal secretions of the infants were removed, the infant lied on his back in a plethysmograph box, and the mask was tightly fastened around the mouth and nose to ensure that there was no air leakage. The test was carried out after the clinical condition of the infant was confirmed to be stable. During the test, blood oxygen saturation was monitored using a percutaneous oximeter. Parents were present during the test. All the infants did not receive respiratory support during the examination of pulmonary function. The following parameters were recorded: weight, length, tidal volume per kilogram of body weight (TV/kg), respiratory rate (RR), volume to peak tidal expiratory flow to total expiratory volume (VPEF/VE), time to peak tidal expiratory flow to total expiratory time (TPEF/tE), compliance of the respiratory system (Crs), compliance of the respiratory system per kilogram of body weight (Crs/kg), resistance of the respiratory system (Rrs), plethysmographic functional residual capacity (FRCp), and specific plethysmographic functional residual capacity (sReff). Five groups of data were collected in each test; the number of groups with a variance coefficient > 10% was manually eliminated, and the average of the remaining groups of data was automatically obtained by the computer. The nitric oxide breath analyzer was used, antibiotics and hormones were forbidden for three days, crying and passive smoking were avoided, and off-line moisture sampling was performed under calm breathing. Expiratory nitric oxide test (FeNO) values were taken as the average value of the three measurements. All infants’ families provided written informed consent. This study was approved by the Ethics Committee of Chengdu Women’s and Children’s Central Hospital (2021/123). SPSS 22.0 statistical software was used to analyze the data. The mean ± SD was used to represent the measurement data conforming to a normal distribution, while the median (P25, P75) was used to represent the measurement data conforming to a non-normal distribution. The independent sample t-test was used to determine whether the two groups of measurement data met the normal distribution and the homogeneity of variance. Otherwise, the non-parametric rank sum test was selected. Counting data was expressed as a component ratio (%) using the Chi-square test or Fisher exact probability method. A one-way analysis of variance was used to compare the three groups. P < 0.05 was considered statistically significant. 3. Results From January 2021 to June 2022, a total of 57 preterm infants met the inclusion criteria, and 60 term infants were hospitalized; their parents agreed to complete a plethysmography pulmonary function test during the same period. Preterm infants were divided into the BPD group (22 cases) and the non-BPD group (35 cases). Preterm infants were further divided into the < 34 weeks group (26 cases) and the 34 ~ 36 + 6 weeks group (31 cases) according to gestational age. According to the 2013 Fenton growth charts [ 13 ] , weight z-scores and length z-scores were calculated to compare the weight and length of preterm and term infants at the time of pulmonary function tests. Table 1 shows that there was a statistical difference between the term group and the preterm group in the choice of mode of delivery, and the number of natural births was higher than that of the preterm infants group. The birth weight and age in months of the preterm group were significantly lower than those of the term group. However, there was no significant difference between the premature group and the term group in weight z-score and length z-score during hospitalization. Table 1 The clinical characteristics between the preterm infants and term infants during hospitalization Preterm infants group (n = 57) Term infants group (n = 60) t/χ2/Z P Male 35 (61.4) 35 (58.3) 0.115 0.735 Vaginal Delivery 23 (40.4) 38 (63.3) 6.187 0.013 Birth weight(g) 2051 ± 591 3298 ± 327 14.012 < 0.001 Weight Z-score 0.91 ± 1.05 0.60 ± 1.04 1.658 0.100 Length Z-score 1.16 ± 1.38 1.62 ± 1.44 -1.775 0.079 Age(month) (1, 5) (1, 3) -2.780 0.005 WBC (10^9) 9.30 ± 2.97 9.16 ± 2.34 0.275 0.784 EOS (10^9) (0.18, 0.43) (0.21, 0.56) -1.734 0.083 Wheezing 5 (8.8) 7 (11.7) 0.266 0.606 Table 2 shows that, compared with the term group, the preterm group had a faster respiratory rate and lower values of TPEF/tE,VPEF/VE,Crs and FRCp. Table 2 Comparison of pulmonary function indexes between preterm and term infant groups Preterm infants group (n = 57) Term infants group (n = 60) t/χ2/Z P RR 40.33 ± 9.56 35.86 ± 7.19 2.867 0.005 TV/kg (ml/kg) (6.85, 8.35) (6.93, 7.90) -0.390 0.696 TPEF/tE (%) (17.70, 26.05) (21.65, 35.95) -3.561 < 0.001 VPEF/VE (%) (21.30, 27.05) (24.03, 34.45) -3.021 0.003 Crs(ml/kPa) (48.47, 80.71) (61.78, 89.81) -2.230 0.026 Crs/kg(ml/kPa/kg) (9.15, 15.25) (11.27, 15.90) -1.909 0.056 Rrs(kPa*s/L) (4.21, 7.63) (4.37, 7.72) -0.633 0.527 FRCp(ml) (56.55, 100.45) (66.65, 130.80) -2.588 0.010 sReff(kPa*s) (0.32, 0.56) (0.27, 0.81) -1.140 0.254 FENO (ppb) (9.00, 17.50) (7.00, 19.00) -0.104 0.917 The results of a one-way analysis of variance and non-parametric rank sum test in Table 3 showed that the differences in RR, TPEF/tE, VPEF/VE, Rrs, and FRCp among the < 34 weeks group, the 34–36 + 6 weeks group and the term infants group were statistically significant (P < 0.05). The respiratory rate in both gestational age groups of preterm infants was significantly faster than that in term infants (P < 0.05). The VPEF/VE values in both gestational age groups of preterm infants were significantly lower than those in term infants (P < 0.05). The < 34 weeks group had the lowest TPEF/tE values and Rrs values, and the difference was statistically significant compared with the other two groups. The FRCp values of the 34 ~ 36 + 6 weeks group were the lowest, and the difference was statistically significant compared with the term group. Table 3 Comparison of pulmonary function indexes in different gestational age groups (x ± s) < 34 weeks group (n = 26) 34 ~ 36 + 6 weeks group (n = 31) term infants group (n = 60) F P RR 41.19 ± 2.42 39.61 ± 8.78 35.86 ± 7.20 a,b 4.340 0.015 TV/kg (ml/kg) (6.97, 9.00) (6.40, 8.30) (6.92, 7.90) 0.986 0.611 TPEF/tE(%) (15.40, 22.15) (19.00, 32.40) a (21.65, 35.95) a 19.199 < 0.001 VPEF/VE(%) (22.50, 30.30) (20.35, 25.95) (24.02, 34.45) a,b 12.751 0.002 Crs(ml/kPa) (50.71, 80.26) (43.17, 81.67) (61.78, 89.81) 5.344 0.069 Crs/kg(ml/kPa/kg) (8.42, 13.60) (9.20, 16.30) (11.27, 15.90) 5.837 0.054 Rrs(kPa*s/L) 5.08 ± 1.74 6.82 ± 2.40 a 6.28 ± 2.34 a 4.478 0.013 FRCp(ml) (59.80, 104.72) (56.40, 100.20) (66.65, 130.80) b 7.134 0.028 sReff(kPa*s) (0.33, 0.55) (0.32, 0.59) (0.27, 0.81) 1.461 0.482 FENO(ppb) (9.00, 18.00) (7.00, 17.00) (7.00, 19.00) 0.089 0.956 a shows that compared with the < 34 weeks group < 0.05, b shows that compared with the 34–36 + 6 weeks group < 0.05. One-way analysis of variance and non-parametric rank sum test results in Table 4 showed statistically significant differences in RR, TPEF/tE, VPEF/VE, Crs, and FRCp among the preterm infants with BPD group, preterm infants without BPD group, and term infants group (P < 0.05). The respiratory rates of the BPD group and the non-BPD group were significantly faster than those of the term infants group (P < 0.05). The Crs values of the preterm without BPD groups were significantly lower than those of the preterm with BPD. The ratio of time to peak tidal expiratory flow to total expiratory time and the ratio of volume to peak tidal expiratory flow to total expiratory volume of the BPD group and non-BPD group were significantly lower than those of the term infants group (P < 0.05). But the Crs values of the BPD group were significantly higher than those of the non-BPD group. Table 4 Comparison of pulmonary function indices in infants with BPD group and non-BPD group (x ± s) Preterm infants with BPD group (n = 22) Preterm infants without BPD group (n = 35) Term infants group (n = 60) F P RR 40.96 ± 12.15 39.94 ± 7.67 35.86 ± 7.20 a,b 4.178 0.018 TV/kg (ml/kg) (6.97, 9.02) (6.40, 8.30) (6.92, 7.90) 1.133 0.567 TPEF/tE(%) (15.40, 21.87) (19.00, 32.60) (21.65, 35.95) a,b 21.704 < 0.001 VPEF/VE(%) (20.00, 25.42) (22.20, 33.50) (24.02, 34.45) a,b 16.838 < 0.001 Crs(ml/kPa) (59.43, 101.25) (43.17, 77.37) a (61.78, 89.81) 9.437 0.009 Crs/kg(ml/kPa/kg) (9.62, 15.15) (9.100, 15.70) (11.27, 15.90) 3.656 0.161 Rrs(kPa*s/L) 6.29 ± 2.34 6.58 ± 2.38 6.28 ± 2.34 2.908 0.059 FRCp(ml) (52.07, 100.30) (56.70, 101.30) (66.65, 130.80) 6.767 0.034 sReff(kPa*s) (0.37, 0.56) (0.31, 0.59) (0.27, 0.81) 1.644 0.439 FENO(ppb) (9.00, 18.00) (9.00, 17.00) (7.00, 19.00) 0.218 0.897 a shows that compared with the BPD preterm group, P < 0.05, and b that compared with the non-BPD preterm group, P < 0.05. 4. Discussion Pulmonary function by plethysmography is the gold standard for detecting functional residual capacity and airway resistance, which can objectively and directly reflect the changes in airway diameter [ 14 ] , is rarely affected by other factors, and is a good method to detect airway obstructive lesions [ 14 ] . It is of great clinical significance in assessing the lung development and prognosis of preterm infants. Understanding the changes in pulmonary function in preterm infants by plethysmography and providing early intervention and treatment are beneficial to the pulmonary development of preterm infants. The plethysmography in this study simultaneously measured tidal breathing pulmonary function and lung volume, and early monitoring of pulmonary function is helpful for evaluating the effects of premature delivery and BPD on lung development in infants. The comparison of baseline clinical data between the term and preterm infants in this study revealed that cesarean sections were performed more frequently in the preterm infants group than in the term infants group. This was considered to be related to the risk factors of preterm delivery, due to the risk of delivery or failure to meet the conditions for a spontaneous delivery, such as breech position; thus, there was a higher number of choices for cesarean section [ 15 ] . Although there were differences in birth weight between the preterm infants group and term infants group, the differences in weight Z-scores and length Z-scores during pulmonary function testing were not statistically significant, making the parameters related to pulmonary function more comparable. We noted that there were no statistically significant differences in gender, white blood cell count, percentage of eosinophils, or wheezing symptoms during hospitalization between the preterm infants and term infants, which made the pulmonary function indicators more comparable. We noted that there were statistically significant differences in RR, TPEF/tE, VPEF/VE, Crs, and FRCp between preterm infants and term infants. RR is known to be co-regulated by chemoreceptors in the respiratory center and peripheral pressure receptors. After birth, the number of small airways will no longer increase but will continue to thicken and lengthen with the growth and development of the lung. The alveolar development is relatively immature, and the force of small airway opening is weak. Preterm infants have a smaller number of alveoli and a smaller lung capacity compared to term infants; their respiratory muscles are underdeveloped, and the compensatory capacity of the lung tissue is limited. Therefore, it is necessary to increase the minute ventilation volume by increasing the respiratory rate to ensure gas exchange in the body. In this study, preterm infants also exhibited a faster respiratory rate, which was different from that of term infants, which was consistent with other studies [ 5 – 6 ] . TPEF/tE refers to the ratio of the time to reach the peak expiratory flow rate to the expiratory time, reflecting the airway diameter and airway obstruction, and the correlation between the VPEF/VE can be up to 90%, both of which are indicators of small airway obstruction. The lower of the TPEF/tE value, the more severe the obstruction [16] . In this study, the differences in TPEF/tE and VPEF/VE between the preterm group and term group were statistically significant, indicating that small airway obstruction was more pronounced in preterm infants. Late preterm infants (34–36 + 6 weeks group) are closer to term infants than early preterm infants (gestational age ≤ 33 + 6 weeks) in body length, weight, and maturity due to the relative maturity of organ development, and the survival rate is also almost the same as that of term infants, which is also referred to as near-term infants. In recent years, there has been an increased number of studies on late preterm infants [ 17 – 18 ] . For this reason, preterm infants were further divided according to gestational week, and the differences in TPEF/tE and VPEF/VE among the < 34 weeks group, the 34–36 + 6 weeks group and the term infants group were statistically significant (P < 0.05). However, when comparing the two groups, we noted that there were no significant differences in TPEF/tE and VPEF/VE between the 34–36 + 6 weeks group and the term infants group, and that small airway obstruction was most obvious in the < 34 weeks group. The reason may be related to the improvement of small airway obstruction in late preterm infants with the increase of corrected gestational weeks, the establishment of individual spontaneous respiration after birth, and the "catch-up growth" of pulmonary function [ 7 ] . After the preterm infants were divided into the preterm infants with BPD group and the preterm infants without BPD group, the differences in TPEF/tE and VPEF/VE of the three groups were measured to be statistically significant (P < 0.05). Further pair-to-pair comparison revealed that there was no significant difference between the BPD group and non-BPD group, indicating that there was no significant difference in the degree of pulmonary function impairment between preterm infants with BPD and without BPD after suffering from respiratory tract infection. Gestational age has a great influence on pulmonary function. A decrease in tidal volume (TV) may occur in restricted lung disease or moderate-to-severe obstructive disease. In our study, there was no significant difference in TV/kg between preterm infants and term infants. When preterm infants were further grouped and compared with term infants again, no significant difference was found, which is consistent with the results of the study by Zhang et al. [ 19 ] , indicating that although there is an increase in airway resistance in preterm infants, the body increases the respiratory rate in order to obtain more tidal volume to meet the normal gas exchange, so there is no significant difference in the tidal volume compared to term infants. FRCp refers to the volume of gas contained in the lung at the end of calm expiration. The influencing factors are related to the elastic retraction force of the lungs, airway resistance, and expiratory time. FRCP is an indicator of lung volume and is important for assessing lung development [ 9 ] . In this study, we noted that compared with that of term infants, the FRCp of preterm infants was lower, and the FRCp of preterm infants with BPD was the lowest. The difference was statistically significant, indicating that preterm infants may have decreased lung volume, and preterm infants with BPD can have significantly decreased lung volume, which is in line with the multiple studies [ 20 – 22 ] . It is suggested that preterm infants, especially preterm infants with BPD, have a higher lung elastic retraction force than healthy term infants, and the expansion of the lung is more difficult, which is related to the elastic fibrosis, limited lung expansion, and increased elastic retraction in infants with BPD. However, there are still a small number of studies with opposite results, such as the study by Schmalisch et al., which determined FRC in 26 non-BPD children and 29 BPD children by infant plethysmography and repeated respiratory inert gas douche, respectively, and revealed that there was no statistical difference in FRC values measured by plethysmography between the two groups [ 5 ] . The analysis may be related to the time of pulmonary function detection and the severity of BPD in the participants. Therefore, whether the severity of BPD can affect lung volumes still needs to be confirmed by further studies. sReff directly reflects airway resistance and is a sensitive index to evaluate airway obstruction in infants and children. The present study demonstrated that although the sReff value of term infants was lower than that of preterm infants, the difference was not statistically significant. The preterm infants were further grouped according to whether BPD occurred, and there was no statistical significance among the three groups, which was inconsistent with the results of other studies [ 6 – 8 ] . It is considered that the majority of preterm infants included in this study are preterm infants with mild BPD, and the sample size of infants with BPD included in this study is relatively small. Crs is an indicator of airway compliance, and in our study, we noted that Crs values were significantly lower in the preterm group compared to the term group, and the difference was statistically significant. Many scholars have conducted relevant studies on whether the respiratory compliance of preterm infants is worse than that of term infants, and a follow-up cohort study revealed that the respiratory compliance of preterm infants at 25 to 33 weeks was 73% of that of term infants, and the difference was not significant at 40 weeks of corrected gestational age [ 23 ] . In another prospective clinical trial, which included 102 preterm infants with an average gestational age of (29 ± 2) weeks, a significant decrease in Crs values was found in preterm infants compared to term infants, and a comparison of infants with BPD to those without BPD revealed a statistically significant difference in Crs values, but the difference in Crs values was not statistically significant between the two groups of infants at a follow-up of corrected gestational age of 4 to 8 months. This may be related to the improvement of respiratory mechanics in infants with BPD as their lungs develop [ 24 ] . This study had some limitations. First, this study was a single-center retrospective study, due to the high requirements for plethysmography pulmonary function measurement, which should be completed in outpatient follow-up after discharge; the sample size was also small, and the results could only reflect the pulmonary function of some preterm infants in our hospital. Second, the number of preterm infants in our study population was comparable to that of term infants. However, when preterm infants were further subdivided according to gestational age and occurrence of BPD, the amount of data in each group was small. This grouping method may have increased the error. Currently, there is a lack of reference values for normal pulmonary function in infants in China, and multi-center, large-scale, long-term follow-up studies are needed. 5. Conclusions There is a certain degree of pulmonary function impairment in preterm infants, which is more severe in early preterm infants. The degree of pulmonary function impairment is greater in preterm infants with BPD than in those without BPD. The next step is to continue to follow up with the study participants to analyze their long-term pulmonary function. Abbreviations BPD: Bronchopulmonary dysplasia Crs: Compliance of the respiratory system Crs/kg: Compliance of the respiratory system per kilogram of body weight EOS: eosinophil FeNO: Expiratory nitric oxide test FRCp: Plethysmographic functional residual capacity Rrs: Resistance of the respiratory system RR: Respiratory rate sReff: Specific plethysmographic functional residual capacity TPEF/tE: Time to peak tidal expiratory flow to total expiratory time TV: tidal volume VPEF/VE: Volume to peak tidal expiratory flow to total expiratory volume WBC: white blood cell Declarations Ethics approval and consent to participate This study was performed in line with the principles of the 1964 Declaration of Helsinki and its later amendments or comparable ethical standards. Approval was granted by the Medical Ethics Committee of Chengdu Women’s and Children’s Central Hospital (approval number: 2021/123). Informed consent was obtained from all families of the infants included in the study. Consent for publication Not applicable. Availability of data and materials The datasets used and/or analysed during the current study are available from the corresponding author on reasonable request. Competing interests The authors declare that they have no competing interests. Funding This work was supported by the Chengdu Municipal Health Commission of Sichuan Province, China (grant no. 2021107) and the Sichuan Medical Association of China (grant no. S21101). Authors' contributions Data extraction from the medical records, XC and FY. Clinical assessment of the patients and follow-ups, AT. Infant pulmonary function testing, LR and DY. Study design and analysis outcomes, ZL and CZ. Writing - original draft, ZL and CZ. All authors have read and agreed to the published version of the manuscript. Acknowledgements We are very grateful to the Chengdu Women’s and Children’s Central Hospital and to the patients and their parents. 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Lung function at 6 and 18 months after preterm birth in relation to severity of bronchopulmonary dysplasia. Pediatr Pulmonol. 2015;50:978-86. Kavvadia V, Greenough A, Dimitriou G, Itakura Y. Lung volume measurements in infants with and without chronic lung disease. Eur J Pediatr. 1998;157:336-9. Fakhoury KF, Sellers C, Smith EO, Rama JA, Fan LL Serial measurements of lung function in a cohort of young children with bronchopulmonary dysplasia. Pediatrics. 2010;125:e1441-7. Hjalmarson O, Sandberg K. Abnormal lung function in healthy preterm infants. Am J Respir Crit Care Med. 2002;165:83-7. Mello RR, Silva KS, Costa AM, Ramos JR. Longitudinal assessment of the lung mechanics of very low birth weight preterm infants with and without bronchopulmonary dysplasia. Sao Paulo Med J. 2015;133:401-7. Cite Share Download PDF Status: Posted Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-3891940","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":269729351,"identity":"bd55652d-a56c-479f-9680-3192fc500664","order_by":0,"name":"Chen Zijin","email":"","orcid":"","institution":"Chengdu Women's and Children's Central Hospital: Chengdu Women and Children's Central Hospital","correspondingAuthor":false,"prefix":"","firstName":"Chen","middleName":"","lastName":"Zijin","suffix":""},{"id":269729352,"identity":"d0436d27-bd78-4d54-a27b-b1bdfc530f76","order_by":1,"name":"Zhang Lei","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAAzElEQVRIiWNgGAWjYBAC+/6GhAMf/9XwyLM3EKnFQOLAw4Mz2I7JGPYcIFYLQ+LjwxxszDYMNxKI1GLOcDjhMAMPGw/jzMcbbzDU2EQT1GLZ3JZwuEBChoddOq3YguFYWm4DQT0HziQcnmEAtGV2jpkEY8NhYrTkfzjMk8DMw3DzDJFaDA4kJBzmOQDUcoOHSC2SMw4kHJzZcIzHsAfolwRi/MLP35D84WNDjb08++GNNz7U2BDhF2RHSiSQohyihVQdo2AUjIJRMDIAAJ14Q77nvsOEAAAAAElFTkSuQmCC","orcid":"https://orcid.org/0000-0001-6598-9014","institution":"Chengdu Women and Children's Central Hospital","correspondingAuthor":true,"prefix":"","firstName":"Zhang","middleName":"","lastName":"Lei","suffix":""},{"id":269729353,"identity":"3d1a3d0f-681c-4ae5-b15c-59fbe875c338","order_by":2,"name":"Ai Tao","email":"","orcid":"","institution":"Chengdu Women's and Children's Central Hospital: Chengdu Women and Children's Central Hospital","correspondingAuthor":false,"prefix":"","firstName":"Ai","middleName":"","lastName":"Tao","suffix":""},{"id":269729354,"identity":"1464f8bb-c484-4506-b9ab-120cbf57759a","order_by":3,"name":"Fan Yinghong","email":"","orcid":"","institution":"Chengdu Women's and Children's Central Hospital: Chengdu Women and Children's Central Hospital","correspondingAuthor":false,"prefix":"","firstName":"Fan","middleName":"","lastName":"Yinghong","suffix":""},{"id":269729355,"identity":"c8b98898-50fa-445e-88e5-ee2f4257612a","order_by":4,"name":"Luo Ronghua","email":"","orcid":"","institution":"Chengdu Women's and Children's Central Hospital: Chengdu Women and Children's Central Hospital","correspondingAuthor":false,"prefix":"","firstName":"Luo","middleName":"","lastName":"Ronghua","suffix":""},{"id":269729356,"identity":"cb6c2db3-623d-4afc-8d53-9965e2335e4c","order_by":5,"name":"Xie Cheng","email":"","orcid":"","institution":"Chengdu Women's and Children's Central Hospital: Chengdu Women and Children's Central Hospital","correspondingAuthor":false,"prefix":"","firstName":"Xie","middleName":"","lastName":"Cheng","suffix":""},{"id":269729357,"identity":"451add41-405d-4766-a21a-0835f176ea4d","order_by":6,"name":"Duan Yaping","email":"","orcid":"","institution":"Chengdu Women's and Children's Central Hospital: Chengdu Women and Children's Central Hospital","correspondingAuthor":false,"prefix":"","firstName":"Duan","middleName":"","lastName":"Yaping","suffix":""}],"badges":[],"createdAt":"2024-01-23 19:57:31","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-3891940/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-3891940/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":59703096,"identity":"8c1b9d86-60e8-457f-b303-4b7f266e3e54","added_by":"auto","created_at":"2024-07-05 05:20:49","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":481725,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-3891940/v1/fbcb53ab-96c5-4c47-8365-2be334bbc146.pdf"}],"financialInterests":"","formattedTitle":"Effects of preterm birth and bronchopulmonary dysplasia on infants’ pulmonary function: A cohort study of 117 infants","fulltext":[{"header":"1. Background","content":"\u003cp\u003eWith the progress of medicine, the survival rate of very preterm infants has been increasing year by year due to the use of antenatal steroids, the improvement of post-natal resuscitation strategies and primary respiratory support, the improvement of nursing care, and the use of post-natal surfactant. However, the incidence of preterm birth is still increasing, and the harms associated with preterm birth still need to be addressed\u003csup\u003e[\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e]\u003c/sup\u003e. The most significant consequences of premature birth are pulmonary damage and neurological impairment. Research has revealed that even in the absence of prolonged mechanical ventilation and oxygen therapy postpartum, preterm birth exerts an adverse influence on lung development\u003csup\u003e[\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e]\u003c/sup\u003e, and pulmonary damage in the neonatal period may have a long-term effect on the respiratory system\u003csup\u003e[\u003cspan additionalcitationids=\"CR3\" citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e]\u003c/sup\u003e. In recent years, there have been many studies about pulmonary function as a method for evaluating pulmonary function damage. Most of these studies focus on pulmonary function in school-aged children; however, there are many factors that cause changes in pulmonary function during growth and development from birth through childhood. However, there are only a few studies on pulmonary function in infants, and the results are not consistent\u003csup\u003e[\u003cspan additionalcitationids=\"CR6 CR7\" citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e]\u003c/sup\u003e. Plethysmography is a technically demanding method to detect pulmonary function. It is a non-invasive method to obtain information about lung volume and airway obstruction that cannot be obtained by spirometry\u003csup\u003e[\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e]\u003c/sup\u003e. The aim of this study was to investigate whether pulmonary function is impaired in preterm infants and whether the degree of pulmonary function impairment is related to the occurrence of bronchopulmonary dysplasia.\u003c/p\u003e"},{"header":"2. Methods","content":"\u003cp\u003eA total of 117 infants hospitalized in the respiratory department of Chengdu Women\u0026rsquo;s and Children's Central Hospital between January 2021 and June 2022 were included in this study. The infants were followed up in the respiratory department one month after discharge with an age of less than 6 months as study participants, including 57 cases in the preterm group and 60 cases in the term group. Preterm infants were divided into the bronchopulmonary dysplasia (BPD) group and the non-BPD group, with 22 cases in the BPD group and 35 cases in the non-BPD group. The diagnosis of BPD was in accordance with the 2019 Jensen Criteria\u003csup\u003e[\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e]\u003c/sup\u003e. BPD was diagnosed when the infant was at 36 weeks\u0026rsquo; postmenstrual age or when the infant was discharged with respiratory support. Preterm infants were divided into the \u0026lt;\u0026thinsp;34 weeks group (26 cases) and the 34\u0026thinsp;~\u0026thinsp;36\u003csup\u003e+\u0026thinsp;6\u003c/sup\u003e weeks group (31 cases) according to gestational age.\u003c/p\u003e \u003cp\u003eExclusion criteria included: (1) infants with symptoms of respiratory infection at the time of pulmonary function testing; (2) serious congenital heart diseases, central nervous system respiratory regulation abnormalities, congenital diaphragmatic hernia, and other myeloid deformities that may affect pulmonary function; (3) test results that did not meet quality control criteria (coefficient of variation of tidal volume or functional residual air volume\u0026thinsp;\u0026gt;\u0026thinsp;10%, and children who did not complete pulmonary function tests); and (4) incomplete data, loss of follow-up, and adverse outcomes.\u003c/p\u003e \u003cp\u003eClinical data collection: (1) production condition, including delivery, birth length, birth weight, and gestational age; and (2) general condition during hospitalization including gender, length, weight, age in months, presence of wheezing, white blood cell (WBC) count, and eosinophil (EOS) count. Infant plethysmography was used to measure pulmonary function in all participants in accordance with the American Thoracic Society/European Respiratory Association guidelines for infant pulmonary function testing\u003csup\u003e[\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e, \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e]\u003c/sup\u003e. Before the test, the instrument was calibrated for ambient temperature, atmospheric pressure, and volume. Before the test, oral and nasal secretions of the infants were removed, the infant lied on his back in a plethysmograph box, and the mask was tightly fastened around the mouth and nose to ensure that there was no air leakage. The test was carried out after the clinical condition of the infant was confirmed to be stable. During the test, blood oxygen saturation was monitored using a percutaneous oximeter. Parents were present during the test. All the infants did not receive respiratory support during the examination of pulmonary function. The following parameters were recorded: weight, length, tidal volume per kilogram of body weight (TV/kg), respiratory rate (RR), volume to peak tidal expiratory flow to total expiratory volume (VPEF/VE), time to peak tidal expiratory flow to total expiratory time (TPEF/tE), compliance of the respiratory system (Crs), compliance of the respiratory system per kilogram of body weight (Crs/kg), resistance of the respiratory system (Rrs), plethysmographic functional residual capacity (FRCp), and specific plethysmographic functional residual capacity (sReff). Five groups of data were collected in each test; the number of groups with a variance coefficient\u0026thinsp;\u0026gt;\u0026thinsp;10% was manually eliminated, and the average of the remaining groups of data was automatically obtained by the computer. The nitric oxide breath analyzer was used, antibiotics and hormones were forbidden for three days, crying and passive smoking were avoided, and off-line moisture sampling was performed under calm breathing. Expiratory nitric oxide test (FeNO) values were taken as the average value of the three measurements. All infants\u0026rsquo; families provided written informed consent. This study was approved by the Ethics Committee of Chengdu Women\u0026rsquo;s and Children\u0026rsquo;s Central Hospital (2021/123).\u003c/p\u003e \u003cp\u003eSPSS 22.0 statistical software was used to analyze the data. The mean\u0026thinsp;\u0026plusmn;\u0026thinsp;SD was used to represent the measurement data conforming to a normal distribution, while the median (P25, P75) was used to represent the measurement data conforming to a non-normal distribution. The independent sample t-test was used to determine whether the two groups of measurement data met the normal distribution and the homogeneity of variance. Otherwise, the non-parametric rank sum test was selected. Counting data was expressed as a component ratio (%) using the Chi-square test or Fisher exact probability method. A one-way analysis of variance was used to compare the three groups. P\u0026thinsp;\u0026lt;\u0026thinsp;0.05 was considered statistically significant.\u003c/p\u003e"},{"header":"3. Results","content":"\u003cp\u003eFrom January 2021 to June 2022, a total of 57 preterm infants met the inclusion criteria, and 60 term infants were hospitalized; their parents agreed to complete a plethysmography pulmonary function test during the same period. Preterm infants were divided into the BPD group (22 cases) and the non-BPD group (35 cases). Preterm infants were further divided into the \u0026lt;\u0026thinsp;34 weeks group (26 cases) and the 34\u0026thinsp;~\u0026thinsp;36\u003csup\u003e+\u0026thinsp;6\u003c/sup\u003e weeks group (31 cases) according to gestational age. According to the 2013 Fenton growth charts\u003csup\u003e[\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e]\u003c/sup\u003e, weight z-scores and length z-scores were calculated to compare the weight and length of preterm and term infants at the time of pulmonary function tests. Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e shows that there was a statistical difference between the term group and the preterm group in the choice of mode of delivery, and the number of natural births was higher than that of the preterm infants group. The birth weight and age in months of the preterm group were significantly lower than those of the term group. However, there was no significant difference between the premature group and the term group in weight z-score and length z-score during hospitalization.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eThe clinical characteristics between the preterm infants and term infants during hospitalization\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"5\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003ePreterm infants group (n\u0026thinsp;=\u0026thinsp;57)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eTerm infants group (n\u0026thinsp;=\u0026thinsp;60)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003et/χ2/Z\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eP\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMale\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e35 (61.4)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e35 (58.3)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.115\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.735\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eVaginal Delivery\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e23 (40.4)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e38 (63.3)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e6.187\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.013\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eBirth weight(g)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e2051\u0026thinsp;\u0026plusmn;\u0026thinsp;591\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e3298\u0026thinsp;\u0026plusmn;\u0026thinsp;327\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e14.012\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e\u0026lt;\u0026thinsp;0.001\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eWeight Z-score\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0.91\u0026thinsp;\u0026plusmn;\u0026thinsp;1.05\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.60\u0026thinsp;\u0026plusmn;\u0026thinsp;1.04\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e1.658\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.100\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eLength Z-score\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e1.16\u0026thinsp;\u0026plusmn;\u0026thinsp;1.38\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e1.62\u0026thinsp;\u0026plusmn;\u0026thinsp;1.44\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e-1.775\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.079\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eAge(month)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e(1, 5)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e(1, 3)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e-2.780\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.005\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eWBC (10^9)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e9.30\u0026thinsp;\u0026plusmn;\u0026thinsp;2.97\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e9.16\u0026thinsp;\u0026plusmn;\u0026thinsp;2.34\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.275\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.784\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eEOS (10^9)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e(0.18, 0.43)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e(0.21, 0.56)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e-1.734\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.083\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eWheezing\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e5 (8.8)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e7 (11.7)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.266\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.606\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eTable\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e shows that, compared with the term group, the preterm group had a faster respiratory rate and lower values of TPEF/tE,VPEF/VE,Crs and FRCp.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab2\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eComparison of pulmonary function indexes between preterm and term infant groups\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"5\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003ePreterm infants group (n\u0026thinsp;=\u0026thinsp;57)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eTerm infants group (n\u0026thinsp;=\u0026thinsp;60)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003et/χ2/Z\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eP\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eRR\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e40.33\u0026thinsp;\u0026plusmn;\u0026thinsp;9.56\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e35.86\u0026thinsp;\u0026plusmn;\u0026thinsp;7.19\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e2.867\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.005\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eTV/kg (ml/kg)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e(6.85, 8.35)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e(6.93, 7.90)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e-0.390\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.696\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eTPEF/tE (%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e(17.70, 26.05)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e(21.65, 35.95)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e-3.561\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e\u0026lt;\u0026thinsp;0.001\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eVPEF/VE (%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e(21.30, 27.05)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e(24.03, 34.45)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e-3.021\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.003\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCrs(ml/kPa)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e(48.47, 80.71)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e(61.78, 89.81)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e-2.230\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.026\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCrs/kg(ml/kPa/kg)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e(9.15, 15.25)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e(11.27, 15.90)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e-1.909\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.056\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eRrs(kPa*s/L)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e(4.21, 7.63)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e(4.37, 7.72)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e-0.633\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.527\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eFRCp(ml)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e(56.55, 100.45)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e(66.65, 130.80)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e-2.588\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.010\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003esReff(kPa*s)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e(0.32, 0.56)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e(0.27, 0.81)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e-1.140\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.254\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eFENO (ppb)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e(9.00, 17.50)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e(7.00, 19.00)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e-0.104\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.917\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eThe results of a one-way analysis of variance and non-parametric rank sum test in Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e showed that the differences in RR, TPEF/tE, VPEF/VE, Rrs, and FRCp among the \u0026lt;\u0026thinsp;34 weeks group, the 34\u0026ndash;36\u003csup\u003e+\u0026thinsp;6\u003c/sup\u003e weeks group and the term infants group were statistically significant (P\u0026thinsp;\u0026lt;\u0026thinsp;0.05). The respiratory rate in both gestational age groups of preterm infants was significantly faster than that in term infants (P\u0026thinsp;\u0026lt;\u0026thinsp;0.05). The VPEF/VE values in both gestational age groups of preterm infants were significantly lower than those in term infants (P\u0026thinsp;\u0026lt;\u0026thinsp;0.05). The \u0026lt;\u0026thinsp;34 weeks group had the lowest TPEF/tE values and Rrs values, and the difference was statistically significant compared with the other two groups. The FRCp values of the 34\u0026thinsp;~\u0026thinsp;36\u003csup\u003e+\u0026thinsp;6\u003c/sup\u003e weeks group were the lowest, and the difference was statistically significant compared with the term group.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab3\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 3\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eComparison of pulmonary function indexes in different gestational age groups (x\u0026thinsp;\u0026plusmn;\u0026thinsp;s)\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"6\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u0026lt;\u0026thinsp;34 weeks group (n\u0026thinsp;=\u0026thinsp;26)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003e34\u0026thinsp;~\u0026thinsp;36\u003csup\u003e+\u0026thinsp;6\u003c/sup\u003e weeks group (n\u0026thinsp;=\u0026thinsp;31)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eterm infants group (n\u0026thinsp;=\u0026thinsp;60)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eF\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eP\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eRR\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e41.19\u0026thinsp;\u0026plusmn;\u0026thinsp;2.42\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e39.61\u0026thinsp;\u0026plusmn;\u0026thinsp;8.78\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e35.86\u0026thinsp;\u0026plusmn;\u0026thinsp;7.20\u003csup\u003ea,b\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e4.340\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e0.015\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eTV/kg (ml/kg)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e(6.97, 9.00)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e(6.40, 8.30)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e(6.92, 7.90)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.986\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e0.611\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eTPEF/tE(%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e(15.40, 22.15)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e(19.00, 32.40)\u003csup\u003ea\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e(21.65, 35.95)\u003csup\u003ea\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e19.199\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e\u0026lt;\u0026thinsp;0.001\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eVPEF/VE(%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e(22.50, 30.30)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e(20.35, 25.95)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e(24.02, 34.45)\u003csup\u003ea,b\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e12.751\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e0.002\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCrs(ml/kPa)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e(50.71, 80.26)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e(43.17, 81.67)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e(61.78, 89.81)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e5.344\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e0.069\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCrs/kg(ml/kPa/kg)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e(8.42, 13.60)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e(9.20, 16.30)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e(11.27, 15.90)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e5.837\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e0.054\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eRrs(kPa*s/L)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e5.08\u0026thinsp;\u0026plusmn;\u0026thinsp;1.74\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e6.82\u0026thinsp;\u0026plusmn;\u0026thinsp;2.40\u003csup\u003ea\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e6.28\u0026thinsp;\u0026plusmn;\u0026thinsp;2.34\u003csup\u003ea\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e4.478\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e0.013\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eFRCp(ml)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e(59.80, 104.72)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e(56.40, 100.20)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e(66.65, 130.80)\u003csup\u003eb\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e7.134\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e0.028\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003esReff(kPa*s)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e(0.33, 0.55)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e(0.32, 0.59)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e(0.27, 0.81)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e1.461\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e0.482\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eFENO(ppb)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e(9.00, 18.00)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e(7.00, 17.00)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e(7.00, 19.00)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.089\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e0.956\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003e \u003csup\u003ea\u003c/sup\u003e shows that compared with the \u0026lt;\u0026thinsp;34 weeks group\u0026thinsp;\u0026lt;\u0026thinsp;0.05, \u003csup\u003eb\u003c/sup\u003e shows that compared with the 34\u0026ndash;36\u003csup\u003e+\u0026thinsp;6\u003c/sup\u003e weeks group\u0026thinsp;\u0026lt;\u0026thinsp;0.05.\u003c/p\u003e \u003cp\u003eOne-way analysis of variance and non-parametric rank sum test results in Table\u0026nbsp;\u003cspan refid=\"Tab4\" class=\"InternalRef\"\u003e4\u003c/span\u003e showed statistically significant differences in RR, TPEF/tE, VPEF/VE, Crs, and FRCp among the preterm infants with BPD group, preterm infants without BPD group, and term infants group (P\u0026thinsp;\u0026lt;\u0026thinsp;0.05). The respiratory rates of the BPD group and the non-BPD group were significantly faster than those of the term infants group (P\u0026thinsp;\u0026lt;\u0026thinsp;0.05). The Crs values of the preterm without BPD groups were significantly lower than those of the preterm with BPD. The ratio of time to peak tidal expiratory flow to total expiratory time and the ratio of volume to peak tidal expiratory flow to total expiratory volume of the BPD group and non-BPD group were significantly lower than those of the term infants group (P\u0026thinsp;\u0026lt;\u0026thinsp;0.05). But the Crs values of the BPD group were significantly higher than those of the non-BPD group.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab4\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 4\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eComparison of pulmonary function indices in infants with BPD group and non-BPD group (x\u0026thinsp;\u0026plusmn;\u0026thinsp;s)\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"6\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003ePreterm infants with BPD group (n\u0026thinsp;=\u0026thinsp;22)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003ePreterm infants without BPD group (n\u0026thinsp;=\u0026thinsp;35)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eTerm infants group (n\u0026thinsp;=\u0026thinsp;60)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eF\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eP\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eRR\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e40.96\u0026thinsp;\u0026plusmn;\u0026thinsp;12.15\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e39.94\u0026thinsp;\u0026plusmn;\u0026thinsp;7.67\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e35.86\u0026thinsp;\u0026plusmn;\u0026thinsp;7.20\u003csup\u003ea,b\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e4.178\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e0.018\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eTV/kg (ml/kg)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e(6.97, 9.02)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e(6.40, 8.30)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e(6.92, 7.90)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e1.133\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e0.567\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eTPEF/tE(%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e(15.40, 21.87)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e(19.00, 32.60)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e(21.65, 35.95)\u003csup\u003ea,b\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e21.704\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e\u0026lt;\u0026thinsp;0.001\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eVPEF/VE(%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e(20.00, 25.42)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e(22.20, 33.50)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e(24.02, 34.45)\u003csup\u003ea,b\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e16.838\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e\u0026lt;\u0026thinsp;0.001\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCrs(ml/kPa)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e(59.43, 101.25)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e(43.17, 77.37)\u003csup\u003ea\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e(61.78, 89.81)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e9.437\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e0.009\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCrs/kg(ml/kPa/kg)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e(9.62, 15.15)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e(9.100, 15.70)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e(11.27, 15.90)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e3.656\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e0.161\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eRrs(kPa*s/L)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e6.29\u0026thinsp;\u0026plusmn;\u0026thinsp;2.34\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e6.58\u0026thinsp;\u0026plusmn;\u0026thinsp;2.38\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e6.28\u0026thinsp;\u0026plusmn;\u0026thinsp;2.34\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e2.908\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e0.059\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eFRCp(ml)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e(52.07, 100.30)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e(56.70, 101.30)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e(66.65, 130.80)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e6.767\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e0.034\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003esReff(kPa*s)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e(0.37, 0.56)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e(0.31, 0.59)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e(0.27, 0.81)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e1.644\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e0.439\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eFENO(ppb)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e(9.00, 18.00)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e(9.00, 17.00)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e(7.00, 19.00)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.218\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e0.897\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003e \u003csup\u003ea\u003c/sup\u003e shows that compared with the BPD preterm group, P\u0026thinsp;\u0026lt;\u0026thinsp;0.05, and \u003csup\u003eb\u003c/sup\u003e that compared with the non-BPD preterm group, P\u0026thinsp;\u0026lt;\u0026thinsp;0.05.\u003c/p\u003e"},{"header":"4. Discussion","content":"\u003cp\u003ePulmonary function by plethysmography is the gold standard for detecting functional residual capacity and airway resistance, which can objectively and directly reflect the changes in airway diameter\u003csup\u003e[\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e]\u003c/sup\u003e, is rarely affected by other factors, and is a good method to detect airway obstructive lesions\u003csup\u003e[\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e]\u003c/sup\u003e. It is of great clinical significance in assessing the lung development and prognosis of preterm infants. Understanding the changes in pulmonary function in preterm infants by plethysmography and providing early intervention and treatment are beneficial to the pulmonary development of preterm infants. The plethysmography in this study simultaneously measured tidal breathing pulmonary function and lung volume, and early monitoring of pulmonary function is helpful for evaluating the effects of premature delivery and BPD on lung development in infants.\u003c/p\u003e \u003cp\u003eThe comparison of baseline clinical data between the term and preterm infants in this study revealed that cesarean sections were performed more frequently in the preterm infants group than in the term infants group. This was considered to be related to the risk factors of preterm delivery, due to the risk of delivery or failure to meet the conditions for a spontaneous delivery, such as breech position; thus, there was a higher number of choices for cesarean section\u003csup\u003e[\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e]\u003c/sup\u003e. Although there were differences in birth weight between the preterm infants group and term infants group, the differences in weight Z-scores and length Z-scores during pulmonary function testing were not statistically significant, making the parameters related to pulmonary function more comparable. We noted that there were no statistically significant differences in gender, white blood cell count, percentage of eosinophils, or wheezing symptoms during hospitalization between the preterm infants and term infants, which made the pulmonary function indicators more comparable.\u003c/p\u003e \u003cp\u003eWe noted that there were statistically significant differences in RR, TPEF/tE, VPEF/VE, Crs, and FRCp between preterm infants and term infants. RR is known to be co-regulated by chemoreceptors in the respiratory center and peripheral pressure receptors. After birth, the number of small airways will no longer increase but will continue to thicken and lengthen with the growth and development of the lung. The alveolar development is relatively immature, and the force of small airway opening is weak. Preterm infants have a smaller number of alveoli and a smaller lung capacity compared to term infants; their respiratory muscles are underdeveloped, and the compensatory capacity of the lung tissue is limited. Therefore, it is necessary to increase the minute ventilation volume by increasing the respiratory rate to ensure gas exchange in the body. In this study, preterm infants also exhibited a faster respiratory rate, which was different from that of term infants, which was consistent with other studies\u003csup\u003e[\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e]\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003eTPEF/tE refers to the ratio of the time to reach the peak expiratory flow rate to the expiratory time, reflecting the airway diameter and airway obstruction, and the correlation between the VPEF/VE can be up to 90%, both of which are indicators of small airway obstruction. The lower of the TPEF/tE value, the more severe the obstruction\u003csup\u003e[16]\u003c/sup\u003e. In this study, the differences in TPEF/tE and VPEF/VE between the preterm group and term group were statistically significant, indicating that small airway obstruction was more pronounced in preterm infants. Late preterm infants (34\u0026ndash;36\u003csup\u003e+\u0026thinsp;6\u003c/sup\u003e weeks group) are closer to term infants than early preterm infants (gestational age\u0026thinsp;\u0026le;\u0026thinsp;33\u003csup\u003e+\u0026thinsp;6\u003c/sup\u003e weeks) in body length, weight, and maturity due to the relative maturity of organ development, and the survival rate is also almost the same as that of term infants, which is also referred to as near-term infants. In recent years, there has been an increased number of studies on late preterm infants\u003csup\u003e[\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e17\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e18\u003c/span\u003e]\u003c/sup\u003e. For this reason, preterm infants were further divided according to gestational week, and the differences in TPEF/tE and VPEF/VE among the \u0026lt;\u0026thinsp;34 weeks group, the 34\u0026ndash;36\u003csup\u003e+\u0026thinsp;6\u003c/sup\u003e weeks group and the term infants group were statistically significant (P\u0026thinsp;\u0026lt;\u0026thinsp;0.05). However, when comparing the two groups, we noted that there were no significant differences in TPEF/tE and VPEF/VE between the 34\u0026ndash;36\u003csup\u003e+\u0026thinsp;6\u003c/sup\u003e weeks group and the term infants group, and that small airway obstruction was most obvious in the \u0026lt;\u0026thinsp;34 weeks group. The reason may be related to the improvement of small airway obstruction in late preterm infants with the increase of corrected gestational weeks, the establishment of individual spontaneous respiration after birth, and the \"catch-up growth\" of pulmonary function\u003csup\u003e[\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e]\u003c/sup\u003e. After the preterm infants were divided into the preterm infants with BPD group and the preterm infants without BPD group, the differences in TPEF/tE and VPEF/VE of the three groups were measured to be statistically significant (P\u0026thinsp;\u0026lt;\u0026thinsp;0.05). Further pair-to-pair comparison revealed that there was no significant difference between the BPD group and non-BPD group, indicating that there was no significant difference in the degree of pulmonary function impairment between preterm infants with BPD and without BPD after suffering from respiratory tract infection. Gestational age has a great influence on pulmonary function.\u003c/p\u003e \u003cp\u003eA decrease in tidal volume (TV) may occur in restricted lung disease or moderate-to-severe obstructive disease. In our study, there was no significant difference in TV/kg between preterm infants and term infants. When preterm infants were further grouped and compared with term infants again, no significant difference was found, which is consistent with the results of the study by Zhang et al.\u003csup\u003e[\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e19\u003c/span\u003e]\u003c/sup\u003e, indicating that although there is an increase in airway resistance in preterm infants, the body increases the respiratory rate in order to obtain more tidal volume to meet the normal gas exchange, so there is no significant difference in the tidal volume compared to term infants.\u003c/p\u003e \u003cp\u003eFRCp refers to the volume of gas contained in the lung at the end of calm expiration. The influencing factors are related to the elastic retraction force of the lungs, airway resistance, and expiratory time. FRCP is an indicator of lung volume and is important for assessing lung development\u003csup\u003e[\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e]\u003c/sup\u003e. In this study, we noted that compared with that of term infants, the FRCp of preterm infants was lower, and the FRCp of preterm infants with BPD was the lowest. The difference was statistically significant, indicating that preterm infants may have decreased lung volume, and preterm infants with BPD can have significantly decreased lung volume, which is in line with the multiple studies\u003csup\u003e[\u003cspan additionalcitationids=\"CR21\" citationid=\"CR19\" class=\"CitationRef\"\u003e20\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e22\u003c/span\u003e]\u003c/sup\u003e. It is suggested that preterm infants, especially preterm infants with BPD, have a higher lung elastic retraction force than healthy term infants, and the expansion of the lung is more difficult, which is related to the elastic fibrosis, limited lung expansion, and increased elastic retraction in infants with BPD.\u003c/p\u003e \u003cp\u003eHowever, there are still a small number of studies with opposite results, such as the study by Schmalisch et al., which determined FRC in 26 non-BPD children and 29 BPD children by infant plethysmography and repeated respiratory inert gas douche, respectively, and revealed that there was no statistical difference in FRC values measured by plethysmography between the two groups\u003csup\u003e[\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e]\u003c/sup\u003e. The analysis may be related to the time of pulmonary function detection and the severity of BPD in the participants. Therefore, whether the severity of BPD can affect lung volumes still needs to be confirmed by further studies.\u003c/p\u003e \u003cp\u003esReff directly reflects airway resistance and is a sensitive index to evaluate airway obstruction in infants and children. The present study demonstrated that although the sReff value of term infants was lower than that of preterm infants, the difference was not statistically significant. The preterm infants were further grouped according to whether BPD occurred, and there was no statistical significance among the three groups, which was inconsistent with the results of other studies\u003csup\u003e[\u003cspan additionalcitationids=\"CR7\" citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e]\u003c/sup\u003e. It is considered that the majority of preterm infants included in this study are preterm infants with mild BPD, and the sample size of infants with BPD included in this study is relatively small.\u003c/p\u003e \u003cp\u003eCrs is an indicator of airway compliance, and in our study, we noted that Crs values were significantly lower in the preterm group compared to the term group, and the difference was statistically significant. Many scholars have conducted relevant studies on whether the respiratory compliance of preterm infants is worse than that of term infants, and a follow-up cohort study revealed that the respiratory compliance of preterm infants at 25 to 33 weeks was 73% of that of term infants, and the difference was not significant at 40 weeks of corrected gestational age\u003csup\u003e[\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e23\u003c/span\u003e]\u003c/sup\u003e. In another prospective clinical trial, which included 102 preterm infants with an average gestational age of (29\u0026thinsp;\u0026plusmn;\u0026thinsp;2) weeks, a significant decrease in Crs values was found in preterm infants compared to term infants, and a comparison of infants with BPD to those without BPD revealed a statistically significant difference in Crs values, but the difference in Crs values was not statistically significant between the two groups of infants at a follow-up of corrected gestational age of 4 to 8 months. This may be related to the improvement of respiratory mechanics in infants with BPD as their lungs develop\u003csup\u003e[\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e24\u003c/span\u003e]\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003eThis study had some limitations. First, this study was a single-center retrospective study, due to the high requirements for plethysmography pulmonary function measurement, which should be completed in outpatient follow-up after discharge; the sample size was also small, and the results could only reflect the pulmonary function of some preterm infants in our hospital. Second, the number of preterm infants in our study population was comparable to that of term infants. However, when preterm infants were further subdivided according to gestational age and occurrence of BPD, the amount of data in each group was small. This grouping method may have increased the error. Currently, there is a lack of reference values for normal pulmonary function in infants in China, and multi-center, large-scale, long-term follow-up studies are needed.\u003c/p\u003e"},{"header":"5. Conclusions","content":"\u003cp\u003eThere is a certain degree of pulmonary function impairment in preterm infants, which is more severe in early preterm infants. The degree of pulmonary function impairment is greater in preterm infants with BPD than in those without BPD. The next step is to continue to follow up with the study participants to analyze their long-term pulmonary function.\u003c/p\u003e"},{"header":"Abbreviations","content":"\u003cp\u003eBPD: Bronchopulmonary dysplasia\u003c/p\u003e\n\u003cp\u003eCrs: Compliance of the respiratory system\u003c/p\u003e\n\u003cp\u003eCrs/kg: Compliance of the respiratory system per kilogram of body weight\u003c/p\u003e\n\u003cp\u003eEOS: eosinophil\u003c/p\u003e\n\u003cp\u003eFeNO: Expiratory nitric oxide test\u003c/p\u003e\n\u003cp\u003eFRCp: Plethysmographic functional residual capacity\u003c/p\u003e\n\u003cp\u003eRrs: Resistance of the respiratory system\u003c/p\u003e\n\u003cp\u003eRR: Respiratory rate\u003c/p\u003e\n\u003cp\u003esReff: Specific plethysmographic functional residual capacity\u003c/p\u003e\n\u003cp\u003eTPEF/tE: Time to peak tidal expiratory flow to total expiratory time\u003c/p\u003e\n\u003cp\u003eTV: tidal volume\u003c/p\u003e\n\u003cp\u003eVPEF/VE: Volume to peak tidal expiratory flow to total expiratory volume\u003c/p\u003e\n\u003cp\u003eWBC: white blood cell\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003eEthics approval and consent to participate\u003c/p\u003e\n\u003cp\u003eThis study was performed in line with the principles of the 1964 Declaration of Helsinki and its later amendments or comparable ethical standards. Approval was granted by the Medical Ethics Committee of Chengdu Women\u0026rsquo;s and Children\u0026rsquo;s Central Hospital (approval number: 2021/123). Informed consent was obtained from all families of the infants included in the study.\u003c/p\u003e\n\u003cp\u003eConsent for publication\u003c/p\u003e\n\u003cp\u003eNot applicable.\u003c/p\u003e\n\u003cp\u003eAvailability of data and materials\u003c/p\u003e\n\u003cp\u003eThe datasets used and/or analysed during the current study are available from the corresponding author on reasonable request.\u003c/p\u003e\n\u003cp\u003eCompeting interests\u003c/p\u003e\n\u003cp\u003eThe authors declare that they have no competing interests.\u003c/p\u003e\n\u003cp\u003eFunding\u003c/p\u003e\n\u003cp\u003eThis work was supported by the Chengdu Municipal Health Commission of Sichuan Province, China (grant no. 2021107) and the Sichuan Medical Association of China (grant no. S21101).\u003c/p\u003e\n\u003cp\u003eAuthors\u0026apos; contributions\u003c/p\u003e\n\u003cp\u003eData extraction from the medical records, XC and FY. Clinical assessment of the patients and follow-ups, AT. Infant pulmonary function testing, LR and DY. Study design and analysis outcomes, ZL and CZ. Writing - original draft, ZL and CZ. All authors have read and agreed to the published version of the manuscript.\u003c/p\u003e\n\u003cp\u003eAcknowledgements\u003c/p\u003e\n\u003cp\u003eWe are very grateful to the Chengdu Women\u0026rsquo;s and Children\u0026rsquo;s Central Hospital and to the patients and their parents.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n \u003cli\u003eOsterman M, Hamilton B, Martin JA, Driscoll AK, Valenzuela CP. Births: final data for 2020. Natl Vital Stat Rep. 2021;70:1-50.\u003c/li\u003e\n \u003cli\u003eKotecha SJ, Dunstan FD, Kotecha S. Long term respiratory outcomes of late preterm-born infants. Semin Fetal Neonatal Med. 2012;17:77-81.\u003c/li\u003e\n \u003cli\u003eCutz E, Chiasson D. Chronic lung disease after premature birth. N Engl J Med. 2008;358:743-5.\u003c/li\u003e\n \u003cli\u003eMoschino L, Stocchero M, Filippone M, Carraro S, Baraldi E. Longitudinal Assessment of lung function in Survivors of Bronchopulmonary Dysplasia from Birth to Adulthood. The Padova BPD study. Am J Respir Crit Care Med. 2018;198:134-7.\u003c/li\u003e\n \u003cli\u003eSchmalisch G, Wilitzki S, Roehr CC, Proquitt\u0026eacute; H, B\u0026uuml;hrer C. Development of lung function in very low birth weight infants with or without bronchopulmonary dysplasia: longitudinal assessment during the first 15 months of corrected age. BMC Pediatr. 2012;12:37\u003c/li\u003e\n \u003cli\u003eSchmalisch G, Wilitzki S, Roehr CC, Proquitt\u0026eacute; H, B\u0026uuml;hrer C. Differential effects of immaturity and neonatal lung disease on the lung function of very low birth weight infants at 48-52 postconceptional weeks. Pediatr Pulmonol. 2013;48:1214-23.\u003c/li\u003e\n \u003cli\u003eLum S, Kirkby J, Welsh L, Marlow N, Hennessy E, Stocks J. Nature and severity of lung function abnormalities in extremely pre-term children at 11 years of age. Eur Respir J. 2011;37:1199-207.\u003c/li\u003e\n \u003cli\u003eYin Yan-dan, et al. Follow-up study on plethysmography in preterm infants aged 1 to 2 years with bronchopulmonary dysplasia. Chin J Evid Based Pediatr. 2016;11:352-6.\u003c/li\u003e\n \u003cli\u003eCri\u0026eacute;e CP, Sorichter S, Smith HJ, Kardos P, Merget R, Heise D, et al. Body plethysmography--its principles and clinical use. Respir Med. 2011;105:959-71.\u003c/li\u003e\n \u003cli\u003eJensen EA, Dysart K, Gantz MG, McDonald S, Bamat NA, Keszler M, et al. The diagnosis of bronchopulmonary dysplasia in very preterm infants. An evidence-based approach. Am J Respir Crit Care Med. 2019;200:751-9.\u003c/li\u003e\n \u003cli\u003eStocks J, Godfrey S, Beardsmore C, Bar-Yishay E, Castile R, ERS/ATS Task Force on Standards for Infant Respiratory Function Testing. European Respiratory Society/American Thoracic Society. Plethysmographic measurements of lung volume and airway resistance. ERS/ATS task force on standards for infant respiratory function testing. European Respiratory Society/ American Thoracic Society. Eur Respir J. 2001;17:302-12.\u003c/li\u003e\n \u003cli\u003eFrey U, Stocks J, Sly P, Bates J. Specification for signal processing and data handling used for infant pulmonary function testing. ERS/ATS task force on standards for infant respiratory function testing. European Respiratory Society/American Thoracic Society. Eur Respir J. 2000;16:1016-22.\u003c/li\u003e\n \u003cli\u003eFenton TR, Kim JH. A systematic review and meta-analysis to revise the Fenton growth chart for preterm infants. BMC Pediatr. 2013;13:59.\u003c/li\u003e\n \u003cli\u003eZysman-Colman Z, Lands LC. Whole Body Plethysmography: Practical considerations. Paediatr Respir Rev. 2016;19:39-41.\u003c/li\u003e\n \u003cli\u003eDi Renzo GC, Cabero Roura L, Facchinetti F, Helmer H, Hubinont C, Jacobsson B, et al. Preterm labor and birth management: recommendations from the European Association of Perinatal Medicine. J Matern Fetal Neonatal Med. 2017;30:2011-30.\u003c/li\u003e\n \u003cli\u003ePaton JY. A practical approach to the interpretation of lung function testing in children. Paediatr Respir Rev. 2000;1:241-8.\u003c/li\u003e\n \u003cli\u003eMuganthan T, Boyle EM. Early childhood health and morbidity, including respiratory function in late preterm and early term births. Semin Fetal Neonatal Med. 2019;24:48-53.\u003c/li\u003e\n \u003cli\u003ePike KC, Lucas JS. Respiratory consequences of late preterm birth. Paediatr Respir Rev. 2015;16:182-8.\u003c/li\u003e\n \u003cli\u003eZhang A, Li G, Wang M, Lin N, Yang S, Zhuang C, Fang X. Pulmonary function of preterm infants with bronchopulmonary dysplasia from 0 to 6 months. Chin Pediatr Emerg Med. 2021;(12):597-602. Chinese.\u003c/li\u003e\n \u003cli\u003eThunqvist P, Gustafsson P, Norman M, Wickman M, Hallberg J. Lung function at 6 and 18 months after preterm birth in relation to severity of bronchopulmonary dysplasia. Pediatr Pulmonol. 2015;50:978-86.\u003c/li\u003e\n \u003cli\u003eKavvadia V, Greenough A, Dimitriou G, Itakura Y. Lung volume measurements in infants with and without chronic lung disease. Eur J Pediatr. 1998;157:336-9.\u003c/li\u003e\n \u003cli\u003eFakhoury KF, Sellers C, Smith EO, Rama JA, Fan LL Serial measurements of lung function in a cohort of young children with bronchopulmonary dysplasia. Pediatrics. 2010;125:e1441-7.\u003c/li\u003e\n \u003cli\u003eHjalmarson O, Sandberg K. Abnormal lung function in healthy preterm infants. Am J Respir Crit Care Med. 2002;165:83-7.\u003c/li\u003e\n \u003cli\u003eMello RR, Silva KS, Costa AM, Ramos JR. Longitudinal assessment of the lung mechanics of very low birth weight preterm infants with and without bronchopulmonary dysplasia. Sao Paulo Med J. 2015;133:401-7.\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"preterm infants, pulmonary function, bronchopulmonary dysplasia","lastPublishedDoi":"10.21203/rs.3.rs-3891940/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-3891940/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003ch2\u003eBackground\u003c/h2\u003e \u003cp\u003eDespite improved preterm infant survival rates in recent years, the increasing prevalence of preterm birth requires ongoing attention to associated risks, especially pulmonary damage. This study explores pulmonary function impairment in preterm infants using plethysmography and examines its correlation with bronchopulmonary dysplasia.\u003c/p\u003e\u003ch2\u003eMethods\u003c/h2\u003e \u003cp\u003eOne hundred and seventeen infants were divided into preterm and term groups, including 57 preterm infants and 60 term infants. Preterm infants were divided into bronchopulmonary dysplasia (BPD) and non-BPD groups. There were 22 cases in the BPD group and 35 cases in the non-BPD group. Preterm infants were further divided into a\u0026thinsp;\u0026lt;\u0026thinsp;34 weeks group and a 34\u0026thinsp;~\u0026thinsp;36\u003csup\u003e+\u0026thinsp;6\u003c/sup\u003e weeks group according to gestational age. There were 26 cases in the \u0026lt;\u0026thinsp;34 weeks group and 31 cases in the 34\u0026thinsp;~\u0026thinsp;36\u003csup\u003e+\u0026thinsp;6\u003c/sup\u003e weeks group. The pulmonary function of each group was measured by plethysmography when the age of the infant was \u0026lt;\u0026thinsp;6 months.\u003c/p\u003e\u003ch2\u003eResults\u003c/h2\u003e \u003cp\u003eCompared with the term group, the preterm group had a significantly higher cesarean section rate and faster respiratory rate (RR) and lower values of the ratio of time to peak tidal expiratory flow to total expiratory time (TPEF/tE), the ratio of volume to peak tidal expiratory flow to total expiratory volume (VPEF/VE), compliance of the respiratory system (Crs), and plethysmographic functional residual capacity (FRCp). Comparisons among infants of different gestational ages revealed statistically significant differences in RR, TPEF/tE, respiratory resistance, VPEF/VE, and FRCp. Comparisons among the three groups of BPD group, non-BPD group, and term group revealed differences in RR, TPEF/tE, VPEF/VE, Crs, and FRCp that were statistically significant.\u003c/p\u003e\u003ch2\u003eConclusions\u003c/h2\u003e \u003cp\u003eThere is a certain degree of pulmonary function impairment in preterm infants, which is more severe in early preterm infants, and in preterm infants with BPD than in preterm infants without BPD. Plethysmography is helpful in the early assessment of pulmonary function in preterm infants.\u003c/p\u003e","manuscriptTitle":"Effects of preterm birth and bronchopulmonary dysplasia on infants’ pulmonary function: A cohort study of 117 infants","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-01-31 06:46:02","doi":"10.21203/rs.3.rs-3891940/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"8bf25961-8e30-4b79-860e-2a3a0bc3746d","owner":[],"postedDate":"January 31st, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2024-07-05T05:04:42+00:00","versionOfRecord":[],"versionCreatedAt":"2024-01-31 06:46:02","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-3891940","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-3891940","identity":"rs-3891940","version":["v1"]},"buildId":"qtupq5eGEP_6zYnWcrvyt","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}