Clinical significance of the overshoot phenomena of respiratory gas indices during recovery from maximal exercise testing

Abstract

BackgroundOvershoot phenomena of the gas exchange ratio (R:VCO2/VO2), ventilatory equivalent for O2 (VE/VO2), and end-tidal O2 pressure (PETO2) are commonly observed during recovery from maximal cardiopulmonary exercise testing (CPX). We investigated the clinical significance of the overshoots of these indices by comparing their magnitudes between healthy subjects and cardiac patients with left ventricular dysfunction. MethodsIn total, 121 subjects (73 healthy subjects and 48 cardiac patients with left ventricular ejection fraction<40%) who underwent CPX and achieved peak R≥1.10 were enrolled. We evaluated and calculated the presence and magnitude of the overshoot phenomena of R, VE/VO2, and PETO2. ResultsThe overshoot phenomena of R, VE/VO2, and PETO2 were observed in all the subjects. The magnitudes of the R (21.4±12.4% vs. 29.3±10.0%, p<0.001), VE/VO2 (45.5±23.5% vs. 77.5±28.5%, p<0.001), and PETO2 (5.3±3.4% vs. 10.1±4.2%, p<0.001) overshoots were significantly lower in cardiac patients than in healthy subjects. In cardiac patients, the magnitude of the PETO2 overshoot showed significant positive correlations with the peak O2 uptake (VO2) (r=0.52, p<0.001), anaerobic threshold (r=0.43, p=0.003), and ratio of the increase in VO2 to the increase in the work rate (r=0.41, p=0.005), and a negative correlation with the slope of the increase in ventilation versus the increase in CO2 output (r=−0.50, p<0.001). The magnitudes of the R and VE/VO2 overshoots showed the same patterns of significant correlation with the CPX indices. ConclusionsWe concluded that the overshoots of R, VE/VO2, and PETO2 during recovery from maximal exercise reflect the natural cardiopulmonary adaptation after exercise and are more prominent in subjects with better cardiopulmonary function.