Abdominal aortic diameter appears unaffected by systemic hypertension in computed tomography measurements in dogs: A Pilot Study

Abdominal aortic diameter appears unaffected by systemic hypertension in computed tomography measurements in dogs: A Pilot Study | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Short Report Abdominal aortic diameter appears unaffected by systemic hypertension in computed tomography measurements in dogs: A Pilot Study Yutaro Ide, Kent Yasunaga, Naoki Miura This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-6175400/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract Dogs with chronically elevated blood pressure require prompt treatment to prevent systemic hypertension-related tissue damage. Non-invasive oscillometry and Doppler sphygmomanometry are the conventional techniques to ascertain this indication, but imaging modalities may potentially enable blood pressure assessments based on vascular geometry. This area is little studied in canine medicine, with only one relevant report on abdominal ultrasonography, and none on computed tomography (CT). Accordingly, we retrospectively evaluated 32 dogs which underwent CT examinations and prior blood pressure measurements on the same day, to determine whether CT-derived abdominal aortic diameter ratios (versus the caudal vena cava [Ao/CVC] and the first lumbar vertebra [Ao/L1]) differed between hypertensive and normotensive dogs. Neither Ao/CVC nor Ao/L1 ratio showed any such significant difference (P = 0.393 or P = 0.229). We concluded that CT-derived abdominal aortic ratios demonstrated no utility for blood pressure assessments in this study population, an inconsistency with previously reported ultrasonographic findings. Our results may reflect that the effect on aortic diameter is indeed small in dogs with systemic hypertension. Further large-scale studies are needed to address this question. computed tomography aorta to caudal vena cava ratio aorta to first lumbar vertebra dog hypertension Figures Figure 1 Figure 2 Introduction Systemic hypertension is generally defined as persistently elevated systolic blood pressure, (Acierno et al, 2018) and is often encountered in clinical settings. In particular, secondary hypertension commands attention in veterinary medicine as it can be related by chronic kidney disease (Pérez-Sánchez et al, 2015 ), hyperadrenocorticism (García San José et al, ,2024), and diabetes (Marynissen et al, 2016 ;), and is often encountered in clinical settings. However, in canine medicine, there is only one report on ultrasonographic determination potential index of systemic hypertension, abdominal aortic diameter to caudal vena cava diameter (Ao/CVC) ratio (Holland et al, 2020). Computed tomography (CT) may offer some advantages that ultrasonography lacks as an imaging modality for measurement of vascular geometry. It allows for objective evaluations and is also a suitable method to ascertain the presence of diseases that may cause secondary hypertension, or identify complications of untreated hypertension, such as cerebral hemorrhage because it is a whole-body imaging method. Based on the advantages of CT, and considering the reported ability of Ao/CVC ratio to reflect systolic blood pressure ultrasonographically, we hypothesized that CT measurements would capture hypertensive changes in abnormal aortic diameter in the same way as ultrasound measurements. To investigate this hypothesis, we retrospectively evaluated dogs that had undergone Doppler blood pressure measurements and CT scans on the same day at our hospital to ascertain any differences in CT-derived Ao/CVC ratio between hypertensive and normotensive dogs, as the primary endpoint in this study. We also established a novel parameter for assessment of aortic geometry, the diametric ratio of the abdominal aorta to the first lumbar vertebra (Ao/L1 ratio), to assure evaluations unaffected by dehydration or anesthesia. . Materials and Methods Study population In this retrospective and descriptive study, we evaluated data from 32 dogs that underwent CT examinations and blood pressure measurements on the same day, while receiving medical care at Kagoshima University Veterinary Teaching Hospital (Kagoshima, Japan) between February and August 2024. Based on a review of its medical records, each dog was designated as hypertensive or normotensive, by an investigator (NM), a veterinarian affiliated to the Diagnostic Imaging Department of Kagoshima University Veterinary Teaching Hospital. Specifically, a dog was classified as normotensive when its systolic blood pressure was ≤ 140 mmHg, or hypertensive when its systolic blood pressure exceeded 140 mmHg. Computed tomography The dogs underwent CT imaging with a dedicated 16-helical sliced CT scanner (Aquilion TSX-201A, Toshiba Medical Systems Corporation, Tochigi, Japan) with (n = 20) or without (n = 12) anesthesia. The anesthesia protocol was determined by the examining veterinarian depending on the patient's condition and temperament. The anesthetics used involved combinations of propofol, dexmedetomidine, butorphanol, and isoflurane; specifically, anesthetized dogs received propofol and isoflurane in 10 cases, and dexmedetomidine and butorphanol in two cases each. Dogs underwent CT imaging in ventral (n = 31) or right lateral (n = 1) recumbency. All images were acquired in DICOM format and were read and measured using a DICOM viewer (OsiriX Ver. 5.9. All observations and measurements were performed by two investigators (YI, KY) under the supervision of the other investigator, and senior veterinarian (NM). All images were taken in plain CT with a slice thickness of 1 mm, usually in the soft tissue condition (WL50:WW350), and the window level and width were changed as necessary. Blood pressure measurement Blood pressure was measured 3–5 times by experienced veterinarians and/or nurses using the Doppler method, with outliers excluded, and the mean of the three measurements was taken as the adopted value. The measurements were taken 20 minutes to one hour after the patient arrived at the hospital, when the patient was confirmed to be calm. Unanesthetized Dogs underwent blood pressure measurement without anesthesia at the same time as physical examination (prior to CT scanning).. When the animal appeared agitated at the time of measurement, this was recorded in its medical record. Imaging measurement and evaluation The dilation of the abdominal aorta was assessed by the ratio of its diameter to the diameter of the caudal vena cava or the first lumbar vertebra (L1). We targeted three sites in the abdomen, for measurement of the diameters of the adjacent aorta and caudal vena (Fig. 1 , A, B, C, D, E). Three anatomical sites targeted for measurement of the diameters of the aorta and caudal vena cava in the abdomen are shown in dorsal (A) and sagittal views (B), with Site 1 at a well-defined location in the abdomen cranial to the origin of the bifurcated external iliac artery (C), Site 2 just below the first lumbar vertebra (E), and Site 3 at a medial point between Sites 1 and 2, and separated by at least five slices from them sites (D). The conditions for this image were soft tissue conditions (WL:50WW:300, slice thickness 1mm). Three anatomical sites targeted for measurement of the diameters of the aorta and caudal vena cava in the abdomen are shown in dorsal (A) and sagittal views (B), with Site 1 at a well-defined location in the abdomen cranial to the origin of the bifurcated external iliac artery (C), Site 2 just below the first lumbar vertebra (E), and Site 3 at a medial point between Sites 1 and 2, and separated by at least five slices from them sites (D). The conditions for this image were soft tissue conditions (WL:50WW:300, slice thickness 1mm) The diameter of the L1 vertebra (F) was measured as a straight line from the longest part of the spinous process to the ventral side of the vertebral body, where it can be clearly observed. The conditions for this image involved a bone conditions (WL:300WW:1500, slice thickness 1mm) The first location (Site 1) was selected in reference to the measurement site determined in a similar report on ultrasonographic measurements (Holland et al, 2020), cranial to the origin of the bifurcated external iliac anatomy. Blood vessel diameters were measured again in the same manner at two different locations in the same region (Sites 2 and 3), to facilitate analytical checks for any error arising due to a change in measurement site. Specifically, Site 2 was at a cranial point on the abdominal blood vessels, adjacent to the L1 vertebra, and Site 3 was at a medial point between Sites 1 and 2. At each measurement site, two notional, perpendicular lines were drawn through the center of each blood vessel extending to its border, and the longer of the two lines was regarded as its maximal diameter, and its measured length was adopted as the value for evaluation. The L1 diameter was measured as the maximum diameter from the vertebra to the spinous process (Fig. 1 F). Statistical analysis Data were analyzed using the statistical analysis software GraphPad Prism version 10.0.2 for Windows (GraphPad Software, La Jolla California USA, www.graphpad.com ), for comparisons between hypertensive and normotensive dogs, between males and females, and anesthetized and unanesthetized dogs, using with student's t test, paired t test. Further comparisons of blood vessel diameters and diameter ratios were made between each of the three measurement sites using with one-way ANOVA. A P value < 0.05 was considered statistically significant. Results Our study population (n = 32) comprised 14 males and 18 females (mean age: 8.8 years; mean body weight: 6.18 kg). Eighteen of the 32 dogs were designated as hypertensive, and the other 14 were designated as normotensive. Hypertensive dogs included eight males and six females (mean age: 8.3 years; mean body weight: 5.8 kg), with a mean systolic blood pressure of 168.7 mmHg (median: 161 mmHg, max: 207 mmHg, min: 142.8 mmHg). Three hypertensive dogs had medical conditions known to predispose for secondary hypertension; specifically, chronic kidney disease (n = 2), and hyperadrenocorticism (n = 1). Otherwise, the hypertensive dogs had been diagnosed with lung tumor (n = 2), liver tumor (n = 1), cervical disc herniation (n = 1), bile duct cystadenoma (n = 1), idiopathic epilepsy (n = 1 ), perineal hernia (n = 1), and cerebral hemorrhage (n = 1), and no diagnosis was made in the other three cases. The detailed cause of the cerebral hemorrhage was not recorded in the diagnosis. Normotensive dogs included seven males and 11 females (mean age: 9.3 years; mean body weight: 6.51 kg) and had a mean systolic blood pressure of 125.3 mmHg (max-min: 140 mmHg − 97.2mm Hg). No normotensive dog was diagnosed with a condition associated with secondary hypertension. No dog had been diagnosed with hypertension or received anti-hypertensive medication prior to the day of imaging. The clinical and demographic characteristics for the study population are provided in Supplementary Table 1. Hypertensive dogs showed mean diameters of 0.69 (0.49–0.97) cm for the abdominal aorta (Site 1), 0.70 (0.42–1.09) cm for the caudal vena cava, and 2.78 (2.14–3.68) cm for L1. Normotensive dogs showed mean diameters of 0.73 (1.09–1.18) cm for the abdominal aorta (Site 1), 0.69 (0.42–1.07) cm for the caudal vena cava, and 2.77 (1.80–4.69) cm for L1. The full data on abdominal aorta and caudal vena (at all three sites) and L1 diameter measurements are presented in Supplemental Table 2. In analysis of the key endpoints, mean Ao/CVC ratio did not differ significantly between hypertensive and normotensive dogs (1.03 [SD: ±0.18] vs. 1.08 [SD: ±0.20]; P = 0.393; Fig. 2 A). Ao/L1 ratio was also assessed (to mitigate against any effect of dehydration on the results), and showed no significant difference between hypertensive and normotensive dogs (0.250 [SD ± 0.028] vs. 0.266 [SD ± 0.041]; P = 0.229; Figure. 2B). Mean Ao/CVC and Ao/L1 ratios in hypertensive and normotensive dogs are represented in box plots, and showed no significant differences (Ao/CVC ratio: P = .393; Ao/L1 ratio: P = .229 > .05; t-test) In other evaluations, we investigated other factors that might potentially be associated with blood pressure or vascular changes. Ao/CVC ratio differed significantly between anaesthetized and unanesthetized dogs (P = 0.03), but Ao/L1 ratio did not (P = 0.95) [Supplemental Fig. 1]. We also evaluated data for each of the three vascular measurement sites (Fig. 1 A, B). Abdominal aortic and caudal vena cava diameters differed significantly between Sites 1 and 2, but we found no significant difference for blood vessel diameters at Site 3 or for Ao/CVC or Ao/L1 ratio at any of three measurement sites (Supplemental Fig. 2). Discussion In this study, we investigated associations between CT-derived abdominal aortic geometry and hypertension in dogs, by evaluating the diametric ratios of the abdominal aorta to the caudal vena cava and L1 vertebra. To the authors’ knowledge, it is the first report on the relationship of CT-derived abdominal aortic diameter with blood pressure, in canine medicine. As key findings in this study, neither Ao/CVC or Ao/L1 ratio appeared able to capture changes in blood pressure level, based on the absence of any significant difference between hypertensive and normotensive dogs in either parameter. The negative results based on CT measurements we report here contrast with a previous report that ultrasonographically measured aortic diameter (based on Ao/CVC ratio) could be indicative of increased blood pressure (Holland et al, 2020). We proposed the Ao/L1 ratio as an indicator of arterial dilation that is not influenced by the patient's hydration status. Since the CVC may be affected by hydration status (Darnis et al., 2018; Herreria-Bustillo et al., 2019; Rabozzi et al., 2020; Combet-Curt et al., 2023), its use as an indicator of vascular dilation may be limited. However, comparisons using vertebral geometry are not subject to such limitations, making them potentially more suitable for arterial assessments. This represents a significant advantage for CT imaging. Additionally, although the effects of anesthesia were a concern in this study, only the Ao/CVC ratio appeared to have been affected. The significant difference between anesthetized and unanesthetized dogs in this parameter suggests some degree of CVC dilatation may have reflected the influence of anesthesia, as has been described previously (Lin et al., 2016). In contrast, the Ao/L1 ratio was indicated to be a reliable indicator for use in comparisons with aortic geometry, as it appeared to be unaffected by dogs’ anesthetization status. In ultrasonographic assessment, the examiner's technique plays a crucial role, with probe pressure reportedly affecting vascular elasticity (Barbot et al., 2019). Standardization of ultrasonographic measurements is thus challenging. Accordingly, CT may enable more objective assessments that are not dependent on individual examiners’ technical skills. In human medicine, essential hypertension is the most prevalent form of hypertension (Vallée et al., 2018 ), whereas in veterinary medicine, secondary hypertension is more common. These differences may affect vascular response. Considering all these points, CT measurements might be expected to provide accurate and objective assessments that address various issues associated with ultrasound. This study has several limitations. One limitation is the relatively small sample size. However, the inability to detect changes in aortic diameter between the two groups with clinically different blood pressure provides valuable insights into the relationship between blood pressure and the abdominal aorta. Furthermore, this study offers essential findings when comparing two groups with varying blood pressures using CT, such as the effects of the measurement site or the anesthetized state. Another significant limitation is that vessel diameters were measured exclusively with CT in this study, without simultaneous ultrasonography measurements. This limitation arises from the retrospective nature of the study, and future cohort studies should focus on comparing two different imaging modalities. In conclusion, we found that abdominal aortic diameter, as measured by CT, appears not to be changed by systemic hypertension. This result suggests that CT measurements of abdominal aortic dilation may not represent a viable approach for assessing cases of suspected systemic hypertension, either because CT cannot capture such hypertension-related changes, or because aortic diameter is not affected by blood pressure in dogs. There is a need for large-scale, simultaneous prospective studies with simultaneous CT and ultrasonographic measurements, to elucidate the true potential utility, or lack of utility, of these imaging modalities for blood pressure assessments. Declarations Acknowledgments We thank all our colleagues at Kagoshima University Veterinary Teaching Hospital for their help in collecting CT images and providing medical care to our patients, our fellow researcher, Nobuhiro Nozaki, for helping with statistical analysis, and Henry Smith (Co-chair of the Veterinary Special Interest Group in the European Medical Writers Association) for helping with the English editing of a draft of the manuscript. Statements & Declarations Funding This research received no external funding. Competing interests The authors declare no competing interests. Author Contributions All authors contributed to the study conception and design. Material preparation, data collection and analysis were performed by Yutaro Ide, Kent Yasunaga and Naoki Miura. The first draft of the manuscript was written by Yutaro Ide and all authors commented on previous versions of the manuscript. All authors read and approved the final manuscript. Data availability The raw data supporting the conclusions of this article will be made available by the authors on request. Ethics approval Ethical review and approval were waived for this study because it did not involve any procedures with experimental animals. It was conducted in accordance with the research ethics bylaws of Kagoshima University. The owner of each dog evaluated in this study had given consent to the use of data in research at the time of medical examinations. Consent to participate and consent for publication Not applicable. References Acierno MJ (2018) ACVIM consensus statement: Guidelines for the identification, evaluation, and management of systemic hypertension in dogs and cats. J Vet Intern Med 32(6):1803–1822. 10.1111/jvim.15331 Bracco MI, Yousefi AAK, Rouet L, Avril S (2025) Ultrasound Probe Pressure Affects Aortic Wall Stiffness: A Patient-Specific Computational Study in Abdominal Aortic Aneurysms. Ann Biomed Eng . 2025;53(1):71–82. 10.1007/s10439-024-03608-8 Combet-Curt J (2023) Ultrasonographic measurement of caudal vena cava to aorta ratio during fluid resuscitation of dogs with spontaneous circulatory shock. J Small Anim Pract 64(11):669–679. 10.1111/jsap.13654 Darnis E (2018) Establishment of reference values of the caudal vena cava by fast-ultrasonography through different views in healthy dogs. J Vet Intern Med 32(4):1308–1318. 10.1111/jvim.15136 García San José P, Pérez-Alenza MD, Alonso-Miguel D, González Sanz S, Arenas Bermejo C (2024) Prevalence of Systemic Hypertension and Control of Systolic Blood Pressure in a Cohort of 14 Dogs with Adrenal-Dependent Hypercortisolism during the First Year of Trilostane Treatment or after Adrenalectomy. Animals (Basel) . 2024;14(3):511. Published 2024 Feb 3. 10.3390/ani14030511 Herreria-Bustillo VJ (2019) Caval-aortic ratio and caudal vena cava diameter in dogs before and after blood donation. J Vet Emerg Crit Care (San Antonio) 29(6):643–646. 10.1111/vec.12900 Holland M (2020) Aortic to caudal vena cava ratio measurements using abdominal ultrasound are increased in dogs with confirmed systemic hypertension. Vet Radiol Ultrasound 61(2):206–214. 10.1111/vru.12822 Marynissen SJ, Smets PM, Ghys LF et al (2016) Long-term follow-up of renal function assessing serum cystatin C in dogs with diabetes mellitus or hyperadrenocorticism. Vet Clin Pathol . 2016;45(2):320–329. 10.1111/vcp.12365 Pérez-Sánchez AP, Del-Angel-Caraza J, Quijano-Hernández IA, Barbosa-Mireles MA (2015) Obesity-hypertension and its relation to other diseases in dogs. Vet Res Commun . 2015;39(1):45–51. 10.1007/s11259-015-9630-9 Rabozzi R (2020) Evaluation of the caudal vena cava diameter to abdominal aortic diameter ratio and the caudal vena cava respiratory collapsibility for predicting fluid responsiveness in a heterogeneous population of hospitalized conscious dogs. J Vet Med Sci 82(3):337–344. 10.1292/jvms.19-0028 Sprouse LR 2nd, Meier GH 3rd, Lesar CJ et al (2003) Comparison of abdominal aortic aneurysm diameter measurements obtained with ultrasound and computed tomography: Is there a difference? J Vasc Surg 38(3):466–472. 10.1016/s0741-5214(03)00367-7 Vallée A, Safar ME, Blacher J (2018) Hypertension artérielle permanente essentielle: définitions et revue hémodynamique, clinique et thérapeutique [Essential hypertension: Definitions, hemodynamic, clinical and therapeutic review]. Presse Med. 2019;48(1 Pt 1):19–28. 10.1016/j.lpm.2018.11.017 Waldrop JE (2003) Aortic dissection associated with aortic aneurysms and posterior paresis in a dog. J Vet Intern Med 17(2):223–229 You J, Li M, Fan W, Li T, Wang J (2022) Effect of different position on inferior vena cava dimensions and its influence on hemodynamics during cesarean section under combined spinal-epidural anesthesia: A randomized controlled trial. J Obstet Gynaecol Res . 2022;48(12):3103–3110. 10.1111/jog.15420 Additional Declarations No competing interests reported. Supplementary Files SupplementalFig1.tif SupplementalFig2.tif SupplementalTable1.tif SupplementalTable2.tif 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. 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hypertension is generally defined as persistently elevated systolic blood pressure, (Acierno et al, 2018) and is often encountered in clinical settings. In particular, secondary hypertension commands attention in veterinary medicine as it can be related by chronic kidney disease (P\u0026eacute;rez-S\u0026aacute;nchez et al, \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2015\u003c/span\u003e), hyperadrenocorticism (Garc\u0026iacute;a San Jos\u0026eacute; et al, ,2024), and diabetes (Marynissen et al, \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e2016\u003c/span\u003e;), and is often encountered in clinical settings. However, in canine medicine, there is only one report on ultrasonographic determination potential index of systemic hypertension, abdominal aortic diameter to caudal vena cava diameter (Ao/CVC) ratio (Holland et al, 2020).\u003c/p\u003e \u003cp\u003eComputed tomography (CT) may offer some advantages that ultrasonography lacks as an imaging modality for measurement of vascular geometry. It allows for objective evaluations and is also a suitable method to ascertain the presence of diseases that may cause secondary hypertension, or identify complications of untreated hypertension, such as cerebral hemorrhage because it is a whole-body imaging method.\u003c/p\u003e \u003cp\u003eBased on the advantages of CT, and considering the reported ability of Ao/CVC ratio to reflect systolic blood pressure ultrasonographically, we hypothesized that CT measurements would capture hypertensive changes in abnormal aortic diameter in the same way as ultrasound measurements. To investigate this hypothesis, we retrospectively evaluated dogs that had undergone Doppler blood pressure measurements and CT scans on the same day at our hospital to ascertain any differences in CT-derived Ao/CVC ratio between hypertensive and normotensive dogs, as the primary endpoint in this study. We also established a novel parameter for assessment of aortic geometry, the diametric ratio of the abdominal aorta to the first lumbar vertebra (Ao/L1 ratio), to assure evaluations unaffected by dehydration or anesthesia.\u003c/p\u003e \u003cp\u003e.\u003c/p\u003e"},{"header":"Materials and Methods","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003eStudy population\u003c/h2\u003e \u003cp\u003eIn this retrospective and descriptive study, we evaluated data from 32 dogs that underwent CT examinations and blood pressure measurements on the same day, while receiving medical care at Kagoshima University Veterinary Teaching Hospital (Kagoshima, Japan) between February and August 2024. Based on a review of its medical records, each dog was designated as hypertensive or normotensive, by an investigator (NM), a veterinarian affiliated to the Diagnostic Imaging Department of Kagoshima University Veterinary Teaching Hospital. Specifically, a dog was classified as normotensive when its systolic blood pressure was \u0026le;\u0026thinsp;140 mmHg, or hypertensive when its systolic blood pressure exceeded 140 mmHg.\u003c/p\u003e \u003c/div\u003e\n\u003ch3\u003eComputed tomography\u003c/h3\u003e\n\u003cp\u003eThe dogs underwent CT imaging with a dedicated 16-helical sliced CT scanner (Aquilion TSX-201A, Toshiba Medical Systems Corporation, Tochigi, Japan) with (n\u0026thinsp;=\u0026thinsp;20) or without (n\u0026thinsp;=\u0026thinsp;12) anesthesia. The anesthesia protocol was determined by the examining veterinarian depending on the patient's condition and temperament. The anesthetics used involved combinations of propofol, dexmedetomidine, butorphanol, and isoflurane; specifically, anesthetized dogs received propofol and isoflurane in 10 cases, and dexmedetomidine and butorphanol in two cases each. Dogs underwent CT imaging in ventral (n\u0026thinsp;=\u0026thinsp;31) or right lateral (n\u0026thinsp;=\u0026thinsp;1) recumbency. All images were acquired in DICOM format and were read and measured using a DICOM viewer (OsiriX Ver. 5.9. All observations and measurements were performed by two investigators (YI, KY) under the supervision of the other investigator, and senior veterinarian (NM). All images were taken in plain CT with a slice thickness of 1 mm, usually in the soft tissue condition (WL50:WW350), and the window level and width were changed as necessary.\u003c/p\u003e\n\u003ch3\u003eBlood pressure measurement\u003c/h3\u003e\n\u003cp\u003eBlood pressure was measured 3\u0026ndash;5 times by experienced veterinarians and/or nurses using the Doppler method, with outliers excluded, and the mean of the three measurements was taken as the adopted value. The measurements were taken 20 minutes to one hour after the patient arrived at the hospital, when the patient was confirmed to be calm. Unanesthetized Dogs underwent blood pressure measurement without anesthesia at the same time as physical examination (prior to CT scanning).. When the animal appeared agitated at the time of measurement, this was recorded in its medical record.\u003c/p\u003e\n\u003ch3\u003eImaging measurement and evaluation\u003c/h3\u003e\n\u003cp\u003eThe dilation of the abdominal aorta was assessed by the ratio of its diameter to the diameter of the caudal vena cava or the first lumbar vertebra (L1).\u003c/p\u003e \u003cp\u003eWe targeted three sites in the abdomen, for measurement of the diameters of the adjacent aorta and caudal vena (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e, A, B, C, D, E).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThree anatomical sites targeted for measurement of the diameters of the aorta and caudal vena cava in the abdomen are shown in dorsal (A) and sagittal views (B), with Site 1 at a well-defined location in the abdomen cranial to the origin of the bifurcated external iliac artery (C), Site 2 just below the first lumbar vertebra (E), and Site 3 at a medial point between Sites 1 and 2, and separated by at least five slices from them sites (D). The conditions for this image were soft tissue conditions (WL:50WW:300, slice thickness 1mm).\u003c/p\u003e \u003cp\u003eThree anatomical sites targeted for measurement of the diameters of the aorta and caudal vena cava in the abdomen are shown in dorsal (A) and sagittal views (B), with Site 1 at a well-defined location in the abdomen cranial to the origin of the bifurcated external iliac artery (C), Site 2 just below the first lumbar vertebra (E), and Site 3 at a medial point between Sites 1 and 2, and separated by at least five slices from them sites (D). The conditions for this image were soft tissue conditions (WL:50WW:300, slice thickness 1mm)\u003c/p\u003e \u003cp\u003eThe diameter of the L1 vertebra (F) was measured as a straight line from the longest part of the spinous process to the ventral side of the vertebral body, where it can be clearly observed. The conditions for this image involved a bone conditions (WL:300WW:1500, slice thickness 1mm)\u003c/p\u003e \u003cp\u003eThe first location (Site 1) was selected in reference to the measurement site determined in a similar report on ultrasonographic measurements (Holland et al, 2020), cranial to the origin of the bifurcated external iliac anatomy. Blood vessel diameters were measured again in the same manner at two different locations in the same region (Sites 2 and 3), to facilitate analytical checks for any error arising due to a change in measurement site. Specifically, Site 2 was at a cranial point on the abdominal blood vessels, adjacent to the L1 vertebra, and Site 3 was at a medial point between Sites 1 and 2.\u003c/p\u003e \u003cp\u003eAt each measurement site, two notional, perpendicular lines were drawn through the center of each blood vessel extending to its border, and the longer of the two lines was regarded as its maximal diameter, and its measured length was adopted as the value for evaluation.\u003c/p\u003e \u003cp\u003eThe L1 diameter was measured as the maximum diameter from the vertebra to the spinous process (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eF).\u003c/p\u003e \u003cdiv id=\"Sec7\" class=\"Section2\"\u003e \u003ch2\u003eStatistical analysis\u003c/h2\u003e \u003cp\u003eData were analyzed using the statistical analysis software GraphPad Prism version 10.0.2 for Windows (GraphPad Software, La Jolla California USA, \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ewww.graphpad.com\u003c/a\u003e\u003c/span\u003e\u003cspan address=\"http://www.graphpad.com\" targettype=\"URL\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e), for comparisons between hypertensive and normotensive dogs, between males and females, and anesthetized and unanesthetized dogs, using with student's t test, paired t test. Further comparisons of blood vessel diameters and diameter ratios were made between each of the three measurement sites using with one-way ANOVA. A P value\u0026thinsp;\u0026lt;\u0026thinsp;0.05 was considered statistically significant.\u003c/p\u003e \u003c/div\u003e"},{"header":"Results","content":"\u003cp\u003eOur study population (n\u0026thinsp;=\u0026thinsp;32) comprised 14 males and 18 females (mean age: 8.8 years; mean body weight: 6.18 kg). Eighteen of the 32 dogs were designated as hypertensive, and the other 14 were designated as normotensive.\u003c/p\u003e \u003cp\u003eHypertensive dogs included eight males and six females (mean age: 8.3 years; mean body weight: 5.8 kg), with a mean systolic blood pressure of 168.7 mmHg (median: 161 mmHg, max: 207 mmHg, min: 142.8 mmHg). Three hypertensive dogs had medical conditions known to predispose for secondary hypertension; specifically, chronic kidney disease (n\u0026thinsp;=\u0026thinsp;2), and hyperadrenocorticism (n\u0026thinsp;=\u0026thinsp;1). Otherwise, the hypertensive dogs had been diagnosed with lung tumor (n\u0026thinsp;=\u0026thinsp;2), liver tumor (n\u0026thinsp;=\u0026thinsp;1), cervical disc herniation (n\u0026thinsp;=\u0026thinsp;1), bile duct cystadenoma (n\u0026thinsp;=\u0026thinsp;1), idiopathic epilepsy (n\u0026thinsp;=\u0026thinsp;1 ), perineal hernia (n\u0026thinsp;=\u0026thinsp;1), and cerebral hemorrhage (n\u0026thinsp;=\u0026thinsp;1), and no diagnosis was made in the other three cases. The detailed cause of the cerebral hemorrhage was not recorded in the diagnosis.\u003c/p\u003e \u003cp\u003eNormotensive dogs included seven males and 11 females (mean age: 9.3 years; mean body weight: 6.51 kg) and had a mean systolic blood pressure of 125.3 mmHg (max-min: 140 mmHg \u0026minus;\u0026thinsp;97.2mm Hg). No normotensive dog was diagnosed with a condition associated with secondary hypertension.\u003c/p\u003e \u003cp\u003eNo dog had been diagnosed with hypertension or received anti-hypertensive medication prior to the day of imaging.\u003c/p\u003e \u003cp\u003eThe clinical and demographic characteristics for the study population are provided in Supplementary Table\u0026nbsp;1.\u003c/p\u003e \u003cp\u003eHypertensive dogs showed mean diameters of 0.69 (0.49\u0026ndash;0.97) cm for the abdominal aorta (Site 1), 0.70 (0.42\u0026ndash;1.09) cm for the caudal vena cava, and 2.78 (2.14\u0026ndash;3.68) cm for L1. Normotensive dogs showed mean diameters of 0.73 (1.09\u0026ndash;1.18) cm for the abdominal aorta (Site 1), 0.69 (0.42\u0026ndash;1.07) cm for the caudal vena cava, and 2.77 (1.80\u0026ndash;4.69) cm for L1. The full data on abdominal aorta and caudal vena (at all three sites) and L1 diameter measurements are presented in Supplemental Table\u0026nbsp;2.\u003c/p\u003e \u003cp\u003eIn analysis of the key endpoints, mean Ao/CVC ratio did not differ significantly between hypertensive and normotensive dogs (1.03 [SD: \u0026plusmn;0.18] vs. 1.08 [SD: \u0026plusmn;0.20]; P\u0026thinsp;=\u0026thinsp;0.393; Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eA). Ao/L1 ratio was also assessed (to mitigate against any effect of dehydration on the results), and showed no significant difference between hypertensive and normotensive dogs (0.250 [SD\u0026thinsp;\u0026plusmn;\u0026thinsp;0.028] vs. 0.266 [SD\u0026thinsp;\u0026plusmn;\u0026thinsp;0.041]; P\u0026thinsp;=\u0026thinsp;0.229; Figure. 2B).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eMean Ao/CVC and Ao/L1 ratios in hypertensive and normotensive dogs are represented in box plots, and showed no significant differences (Ao/CVC ratio: P\u0026thinsp;=\u0026thinsp;.393; Ao/L1 ratio: P\u0026thinsp;=\u0026thinsp;.229\u0026thinsp;\u0026gt;\u0026thinsp;.05; t-test)\u003c/p\u003e \u003cp\u003eIn other evaluations, we investigated other factors that might potentially be associated with blood pressure or vascular changes. Ao/CVC ratio differed significantly between anaesthetized and unanesthetized dogs (P\u0026thinsp;=\u0026thinsp;0.03), but Ao/L1 ratio did not (P\u0026thinsp;=\u0026thinsp;0.95) [Supplemental Fig.\u0026nbsp;1].\u003c/p\u003e \u003cp\u003eWe also evaluated data for each of the three vascular measurement sites (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eA, B). Abdominal aortic and caudal vena cava diameters differed significantly between Sites 1 and 2, but we found no significant difference for blood vessel diameters at Site 3 or for Ao/CVC or Ao/L1 ratio at any of three measurement sites (Supplemental Fig.\u0026nbsp;2).\u003c/p\u003e"},{"header":"Discussion","content":"\u003cp\u003eIn this study, we investigated associations between CT-derived abdominal aortic geometry and hypertension in dogs, by evaluating the diametric ratios of the abdominal aorta to the caudal vena cava and L1 vertebra. To the authors\u0026rsquo; knowledge, it is the first report on the relationship of CT-derived abdominal aortic diameter with blood pressure, in canine medicine.\u003c/p\u003e \u003cp\u003eAs key findings in this study, neither Ao/CVC or Ao/L1 ratio appeared able to capture changes in blood pressure level, based on the absence of any significant difference between hypertensive and normotensive dogs in either parameter. The negative results based on CT measurements we report here contrast with a previous report that ultrasonographically measured aortic diameter (based on Ao/CVC ratio) could be indicative of increased blood pressure (Holland et al, 2020).\u003c/p\u003e \u003cp\u003eWe proposed the Ao/L1 ratio as an indicator of arterial dilation that is not influenced by the patient's hydration status. Since the CVC may be affected by hydration status (Darnis et al., 2018; Herreria-Bustillo et al., 2019; Rabozzi et al., 2020; Combet-Curt et al., 2023), its use as an indicator of vascular dilation may be limited. However, comparisons using vertebral geometry are not subject to such limitations, making them potentially more suitable for arterial assessments. This represents a significant advantage for CT imaging. Additionally, although the effects of anesthesia were a concern in this study, only the Ao/CVC ratio appeared to have been affected. The significant difference between anesthetized and unanesthetized dogs in this parameter suggests some degree of CVC dilatation may have reflected the influence of anesthesia, as has been described previously (Lin et al., 2016). In contrast, the Ao/L1 ratio was indicated to be a reliable indicator for use in comparisons with aortic geometry, as it appeared to be unaffected by dogs\u0026rsquo; anesthetization status.\u003c/p\u003e \u003cp\u003eIn ultrasonographic assessment, the examiner's technique plays a crucial role, with probe pressure reportedly affecting vascular elasticity (Barbot et al., 2019). Standardization of ultrasonographic measurements is thus challenging. Accordingly, CT may enable more objective assessments that are not dependent on individual examiners\u0026rsquo; technical skills. In human medicine, essential hypertension is the most prevalent form of hypertension (Vall\u0026eacute;e et al., \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e2018\u003c/span\u003e), whereas in veterinary medicine, secondary hypertension is more common. These differences may affect vascular response. Considering all these points, CT measurements might be expected to provide accurate and objective assessments that address various issues associated with ultrasound.\u003c/p\u003e \u003cp\u003eThis study has several limitations. One limitation is the relatively small sample size. However, the inability to detect changes in aortic diameter between the two groups with clinically different blood pressure provides valuable insights into the relationship between blood pressure and the abdominal aorta. Furthermore, this study offers essential findings when comparing two groups with varying blood pressures using CT, such as the effects of the measurement site or the anesthetized state. Another significant limitation is that vessel diameters were measured exclusively with CT in this study, without simultaneous ultrasonography measurements. This limitation arises from the retrospective nature of the study, and future cohort studies should focus on comparing two different imaging modalities.\u003c/p\u003e \u003cp\u003eIn conclusion, we found that abdominal aortic diameter, as measured by CT, appears not to be changed by systemic hypertension. This result suggests that CT measurements of abdominal aortic dilation may not represent a viable approach for assessing cases of suspected systemic hypertension, either because CT cannot capture such hypertension-related changes, or because aortic diameter is not affected by blood pressure in dogs. There is a need for large-scale, simultaneous prospective studies with simultaneous CT and ultrasonographic measurements, to elucidate the true potential utility, or lack of utility, of these imaging modalities for blood pressure assessments.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAcknowledgments\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eWe thank all our colleagues at Kagoshima University Veterinary Teaching Hospital for their help in collecting CT images and providing medical care to our patients, our fellow researcher, Nobuhiro Nozaki, for helping with statistical analysis, and Henry Smith (Co-chair of the Veterinary Special Interest Group in the European Medical Writers Association) for helping with the English editing of a draft of the manuscript.\u003c/p\u003e\n\u003cp\u003eStatements \u0026amp; Declarations\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis research received no external funding.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCompeting interests\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare no competing interests.\u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthor Contributions\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eAll authors contributed to the study conception and design. Material preparation, data collection and analysis were performed by Yutaro Ide, Kent Yasunaga and Naoki Miura. The first draft of the manuscript was written by Yutaro Ide and all authors commented on previous versions of the manuscript. All authors read and approved the final manuscript.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eData availability\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe raw data supporting the conclusions of this article will be made available by the authors on request.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eEthics approval\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eEthical review and approval were waived for this study because it did not involve any procedures with experimental animals. It was conducted in accordance with the research ethics bylaws of Kagoshima University. The owner of each dog evaluated in this study had given consent to the use of data in research at the time of medical examinations.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConsent to participate and consent for publication\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNot applicable.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eAcierno MJ (2018) ACVIM consensus statement: Guidelines for the identification, evaluation, and management of systemic hypertension in dogs and cats. 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J Vet Intern Med 17(2):223\u0026ndash;229\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eYou J, Li M, Fan W, Li T, Wang J (2022) Effect of different position on inferior vena cava dimensions and its influence on hemodynamics during cesarean section under combined spinal-epidural anesthesia: A randomized controlled trial. \u003cem\u003eJ Obstet Gynaecol Res\u003c/em\u003e. 2022;48(12):3103\u0026ndash;3110. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1111/jog.15420\u003c/span\u003e\u003cspan address=\"10.1111/jog.15420\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\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":"computed tomography, aorta to caudal vena cava ratio, aorta to first lumbar vertebra, dog, hypertension","lastPublishedDoi":"10.21203/rs.3.rs-6175400/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-6175400/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eDogs with chronically elevated blood pressure require prompt treatment to prevent systemic hypertension-related tissue damage. Non-invasive oscillometry and Doppler sphygmomanometry are the conventional techniques to ascertain this indication, but imaging modalities may potentially enable blood pressure assessments based on vascular geometry. This area is little studied in canine medicine, with only one relevant report on abdominal ultrasonography, and none on computed tomography (CT). Accordingly, we retrospectively evaluated 32 dogs which underwent CT examinations and prior blood pressure measurements on the same day, to determine whether CT-derived abdominal aortic diameter ratios (versus the caudal vena cava [Ao/CVC] and the first lumbar vertebra [Ao/L1]) differed between hypertensive and normotensive dogs. Neither Ao/CVC nor Ao/L1 ratio showed any such significant difference (P\u0026thinsp;=\u0026thinsp;0.393 or P\u0026thinsp;=\u0026thinsp;0.229). We concluded that CT-derived abdominal aortic ratios demonstrated no utility for blood pressure assessments in this study population, an inconsistency with previously reported ultrasonographic findings. Our results may reflect that the effect on aortic diameter is indeed small in dogs with systemic hypertension. Further large-scale studies are needed to address this question.\u003c/p\u003e","manuscriptTitle":"Abdominal aortic diameter appears unaffected by systemic hypertension in computed tomography measurements in dogs: A Pilot Study","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-03-18 12:26:28","doi":"10.21203/rs.3.rs-6175400/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":"98811d2e-652d-4ed3-9525-bbc13735e61c","owner":[],"postedDate":"March 18th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2025-04-05T23:38:16+00:00","versionOfRecord":[],"versionCreatedAt":"2025-03-18 12:26:28","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-6175400","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-6175400","identity":"rs-6175400","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}