Overshoot Phenomena of Respiratory Gas Variables During Exercise Recovery in Cardiac Patients

Background: Transient increases (overshoot) in respiratory gas variables have been observed during exercise recovery, but their clinical significance is not clearly understood. Our group evaluated the relationship between the presence of overshoot of respiratory gas variables and the parameters obtained from cardiopulmonary exercise testing (CPX). Methods and Results: In total, 227 patients with various cardiac diseases underwent CPX. The overshoot phenomena of O2 uptake (VO2), VO2/heart rate (O2-pulse), and CO2 output (VCO2) were analyzed by respiratory gas analysis during recovery after maximal exercise. The overshoot of VO2, O2-pulse, and VCO2 were recognized in 11 (5%), 43 (19%), and 12 (5%) patients, respectively. Compared with the patients without a VO2 overshoot, those with a VO2 overshoot had a significantly lower peak VO2 (12.3±3.7 vs. 17.9±6.2ml·min-1·kg-1, P=0.003), lower anaerobic threshold (9.4±1.7 vs. 12.4±3.3ml·min-1·kg-1, P=0.001), higher VE-VCO2 slope (38.0±5.2 vs. 33.2±9.6, P=0.013), and lower left ventricular ejection fraction (LVEF) (39.9±22.8 vs. 55.8±16.8%, P=0.003). Similar findings were obtained for the patients with an O2-pulse overshoot and those with a VCO2 overshoot. Conclusions: The overshoot phenomena of respiratory gas variables during recovery after maximal exercise are correlated with impaired cardiopulmonary function during exercise in cardiac patients. (Circ J 2012; 76: 876-883)