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

Background: Overshoot phenomena of the gas exchange ratio (R:VCO/VO), ventilatory equivalent for O (VE/VO), and end-tidal O pressure (PETO) 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.

Methods: In 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/VO, and PETO.

Results: The overshoot phenomena of R, VE/VO, and PETO were observed in all the subjects. The magnitudes of the R (21.4±12.4% vs. 29.3±10.0%, p<0.001), VE/VO (45.5±23.5% vs. 77.5±28.5%, p<0.001), and PETO (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 PETO overshoot showed significant positive correlations with the peak O uptake (VO) (r=0.52, p<0.001), anaerobic threshold (r=0.43, p=0.003), and ratio of the increase in VO 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 CO output (r=-0.50, p<0.001). The magnitudes of the R and VE/VO overshoots showed the same patterns of significant correlation with the CPX indices.

Conclusions: We concluded that the overshoots of R, VE/VO, and PETO during recovery from maximal exercise reflect the natural cardiopulmonary adaptation after exercise and are more prominent in subjects with better cardiopulmonary function.