Blunted responses of Doppler-derived aortic flow parameters during whole-body heavy isometric exercise in heart transplant recipients

Relatively light isometric exercise (handgrip) in heart transplant recipients induces attenuated increments in heart rate, blood pressure, and systemic vascular resistance, but hemodynamic response to whole-body, heavy isometric exercise is unknown. The aim of our study was to investigate the influences of whole-body, heavy, isometric exercise on Doppler-derived parameters in these patients. We investigated 18 patients, aged 54.0 ± 2 years, 1.6 ± 1.0 years after cardiac transplantation and 18 sedentary healthy volunteers, aged 51.8 ± 4 years ( p = not significant). Patients performed supine, isometric exercise by stretching a whole-body isometric device at 50% of maximal voluntary contraction for 3 minutes. Resting heart rate, blood pressure, and rate-pressure product were higher in transplanted patients when compared with the healthy volunteers ( p < 0.001 for all). However, during isometric exercise, these parameters increased to a lesser extent in the transplanted compared with the healthy subjects—heart rate, 12% vs 40% ( p < 0.001); mean arterial pressure, 20% vs 27% ( p < 0.05); and rate-pressure product, 39% vs 85% ( p < 0.001). In the healthy volunteers, peak-flow velocity, mean acceleration, flow-velocity integral, and stroke volume decreased by 30% to 40% with isometric exercise ( p < 0.001 for all), whereas systemic vascular resistance increased by 36% ( p < 0.001) and cardiac output did not change. In the transplanted patients, all above parameters remained unchanged. Heavy, whole-body isometric exercise was well tolerated in heart transplant recipients in this study, without hemodynamic deterioration or other complications. With whole-body, heavy isometric exercise, Doppler-derived aortic flow parameters demonstrate blunted responses or remain unchanged among heart transplant recipients. The observed phenomenon may have implications for studies of exercise physiology in transplant recipients.