Delayed attainment of peak oxygen consumption after the end of exercise in patients with chronic heart failure

Peak oxygen uptake (VO2) is attained at peak exercise in normal subjects. Recently, it was shown that the kinetics of the VO2 increase during exercise is slowed in chronic heart failure (CHF). We hypothesized that this may delay maximal VO2 after the end of exercise. We studied 21 patients who attained their peak VO2 15 s or more after cessation of a graded bicycle exercise test with breath-by-breath gas analysis (group 1). They were compared with 21 age- and sex-matched CHF patients who did not do so (group 2) and 21 normal subjects (group 3). Peak VO2 occurred 30 +/- 10 s (15-45) after exercise and was 10 +/- 7% (3-31) higher than end-exercise VO2 (P < 0.001) in group 1. Group 1 patients had poorer functional status (NYHA class 3.0 +/- 0.2 vs. 2.4 +/- 0.5), a smaller ejection fraction (21 +/- 6 vs. 26 +/- 8%), a lower end-exercise VO2 (1156 +/- 251 vs. 1535 +/- 508 ml/min), a lower anaerobic threshold (762 +/- 183 vs. 970 +/- 265 ml/min), and an identical respiratory exchange ratio (1.09 +/- 0.13 vs. 1.06 +/- 0.12) relative to group 2 patients. The delta VO2/delta workrate ratio was lower (9.5 +/- 2.0 vs. 11.2 +/- 1.1 ml/W) and the half-time of VO2 recovery was longer (156 +/- 27 vs. 95 +/- 27 s) in group 1 than in group 2 (P < 0.05, P < 0.01 group 1 vs. group 2). Slow kinetics of the VO2 increase with exercise may delay achievement of peak VO2 beyond the maximal workrate achieved. Gas exchanges should thus be measured also during recovery so as not to underestimate the true peak VO2, especially in severe CHF patients referred for heart transplantation.