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±3.3 ml·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.