Serial assessment of peak VO2 and VO2 kinetics early after heart transplantation

PURPOSE: Serial evaluation of aerobic metabolism and exercise tolerance early after heart transplantation (HT). METHODS: Fifteen heart transplant recipients (HTR), aged 52.0 +/- 9.9 yr (mean +/- SD), not undergoing structured rehabilitation programs, were tested two to four times during the first 2 yr post-HT. As a reference, a group of 11 healthy untrained controls (C) was utilized. Peak heart rate (peak HR), peak O2 uptake (peak VO2), and ventilatory threshold (VT) were determined during incremental bicycle exercise to voluntary exhaustion. VO2 kinetics were evaluated during constant-load exercise below VT, with determination of the duration of the "cardiodynamic" component (TDp) and of the time constant of the "primary" component (taup). RESULTS: Peak VO2 (L.min-1) was positively related to months post-HT (y=1.17 + 0.02x, P=0.003), and it increased by approximately 30% during the investigated period, although values in HTR were lower than in C (2.19 +/- 0.24). Peak HR was lower in HTR (136 +/- 15 beats.min-1) than in C (168 +/- 5), and it was not related to time post-HT. TDp was longer in HTR (31.4 +/- 6.3 s) than in C (23.2 +/- 6.1), and it was not related to time post-HT. A subgroup of HTR with markedly longer taup during the first months post-HT showed a significant decrease of this parameter as a function of time post-HT. CONCLUSIONS: Aerobic metabolism is impaired in HTR. Both central (cardiovascular) and peripheral (skeletal muscle) factors contribute to the reduced exercise tolerance. HTR showed, during the first 2 yr post-HT, a significant increase in peak VO2 and (in the patients with the slowest VO2 kinetics during the first months after HT) a significant improvement of the VO2 kinetics. The main gains seem to occur at the peripheral level.