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 b een recommended for exercise testing in denervated posttransplantation heart recipients. However, how the exercise protocol influences the h emodynamic, gas exchange, and hormonal response to exercise in this po pulation has not been studied. Methods: Nine heart transplant recipien ts were tested with two incremental maximal bicycle ergometry tests in random order. Exercise stages of 1 and 3 minute durations were compar ed with matched work rate increments ranging between 30 and 40 W. Expi ratory gas was measured continuously and arterial blood was sampled at each of the matched work rates. Results: Total exercise duration was 6.4 +/- 0.3 and 15.3 +/- 0.7 minutes for the 1-minute and 5-minute pro tocols, respectively. Maximal workload was significantly higher during the 1-minute versus the 3-minute protocol (238 +/- 9 versus 200 +/- 1 1 W, p < 0.001), but maximal oxygen uptake was not significantly diffe rent (25.5 +/- 1.1 versus 26.5 +/- 1.2 ml . min(-1). kg(-1)). Hemodyna mic, metabolic, and some hormonal parameters showed marked differences between the two protocols, with significantly higher responses observ ed during the 3-minute protocol for heart rate, ventilation, lactate, atrial natriuretic factor, and growth hormone. Catecholamine (epinephr ine and norepinephrine) and insulin responses did not differ between t he two tests. If expressed as a relative exercise intensity (percentag e 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: Alth ough 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 signific ant 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.