Influence of the exercise protocol on hemodynamic, gas exchange, and neurohumoral responses to exercise in heart transplant recipients.

BACKGROUND

A gradual accommodation to increasing exercise loads has been recommended for exercise testing in denervated posttransplantation heart recipients. However, how the exercise protocol influence the hemodynamic, gas exchange, and hormonal response to exercise in this not been studied.

METHODS

Nine heart transplant recipients tests incremental maximal bicycle ergometry tests in random order. Exercise stages of 1 and 3 minute durations were compared with matched work rate increments ranging between 30 and 40 W. Expiratory gas was measured continuously and arterial blood was sampled at each of the matched work rates.

RESULTS

Total exercise duration was 6.4 +/- and 15.3 +/- 0.7 minutes for the 1-minute and 3-minute protocols, respectively. Maximal workload was significantly higher during the 1-minute versus the 3-minute protocol (238 +/- 9 versus 200 +/- 11 W, p < 0.001), but maximal oxygen uptake was not significantly different (25.5 +/- 1.1 versus 26.5 +/- 1.2 ml. min-1.kg-1). Hemodynamic, metabolic, and some hormonal parameters showed marked differences between the two protocols, with significantly higher responses observed during the 3-minute protocol for heart rate, ventilation, lactate, atrial natriuretic factor, and growth hormone. Catecholamine (epinephrine and norepinephrine) and insulin responses did not differ between the two tests. If expressed as a relative exercise intensity (percentage of maximal oxygen uptake) no differences in hormonal responses were observed between the two protocols, except for growth hormone response which remained higher during the 3-minute protocol.

CONCLUSIONS

Although maximal oxygen uptake was independent of the exercise protocol in these heart transplant recipients, the exercise protocol has a major influence on the hormonal and metabolic response. The delayed response observed for oxygen uptake and hormonal responses suggests a significant physiologic lag time during the more rapidly incremental protocol. These differences should be taken into account when exercise is used as a method to evaluate the heart transplant recipient.