Detection of dynamic lung hyperinflation using cardiopulmonary exercise testing and respiratory function in patients with stable cardiac disease: a multicenter cross-sectional study

Background: Many patients with heart disease potentially have comorbid COPD, however there are not enough opportunities for screening and the qualitative differentiation of shortness of breath (SOB) has not been well established. We investigated the detection rate of SOB based on a visual and qualitative dynamic lung hyperinflation (DLH) detection index during cardiopulmonary exercise testing (CPET) and whether there was a difference in respiratory function between the two groups. Methods We recruited 534 patients with heart disease and to scrutinize physical functions (369 males, 67.0 ± 12.9 years) who underwent CPET and spirometry simultaneously. The difference between inspiratory and expiratory tidal volume was calculated (TV E-I) from the breath-by-breath data. A TV E-I decrease after the start of exercise comprised the convex group, and a TV E-I that remained unchanged or increased comprised the non-convex group. Results 129 patients (24.2%) were in the convex; there was no difference in clinical characteristics between groups. The Borg scale scores at the end of the CPET showed no difference. VE/VCO 2 slope, its Y-intercept and minimum VE/VCO 2 showed no significant difference. In the convex group, FEV1.0% was significantly lower (69.4 ± 13.1 vs. 75.0 ± 9.0%), and FEV1.0% and Y-intercept and the difference between minimum VE/VCO 2 and VE/VCO 2 slope were significantly correlated (r=-0.343 and r=-0.478). Conclusions The convex group showed decreased respiratory function, suggesting potential airway obstruction during exercise. A combined assessment of the TV E-I and Y-intercept of the VE/VCO 2 slope or the difference between the minimum VE/VCO 2 and VE/VCO 2 slopes could potentially detect COPD or airway obstruction.