Hemodynamic responses to upright exercise of adolescent cardiac transplant recipients

To characterize the hemodynamic response to exercise after cardiac transplantation, we asked seven adolescent transplant patients (aged 15.1 +/- 0.7 years; mean +/- SE) to perform upright discontinuous exercise to volitional exhaustion on a mechanically braked cycle ergometer. Data were compared with those of seven control subjects matched for age, gender, body mass, percentage of fat, and body surface area. The transplant group had lower peak power output values (92 +/- 13 vs 146 +/- 30 watts; p less than or equal to 0.001) and maximum oxygen consumption values (22 +/- 8 vs 32 +/- 8 ml/kg per minute; p less than or equal to 0.03), despite achieving the same peak venous lactic acid concentration (6.2 +/- 3 vs 5.9 +/- 3 mEq/L; p = not significant). The transplant group had a diminished heart rate in response to exercise--44% lower than the control group had (delta = 49 +/- 6.4 vs 87 +/- 9.1 beats/min; p = 0.005). The cardiac output response to exercise was maintained in the transplant group (delta = 6.5 +/- 1.5 vs 4.6 +/- 0.8 L/min; p = not significant) by an augmented stroke volume response (delta = 31 +/- 10 vs -4 +/- 3.4 ml; p = 0.01), which may relate to a greater decrease in systemic vascular resistance during exercise (delta = -13.7 +/- 2.2 vs -6.3 +/- 1.2 Wood units; p = 0.02). Thus adolescents who have undergone cardiac transplantation have a normal cardiac output response to upright exercise. This is accomplished, despite a blunted heart rate response, by an augmented stroke volume that may relate to the greater decrease in systemic resistance during exercise.