Cardiovascular responses to incremental and sustained submaximal exercise in heart transplant recipients

The cardiovascular response to exercise in heart transplant recipients (HTR) has been compared with that of healthy individuals matched to the recipient age (RM controls). However, no study has compared HTR with donor age-matched (DM) controls. Moreover, the cardiovascular response to sustained submaxi- mal exercise in HTR requires further evaluation. We therefore examined cardiovascular responses during incremental exercise and sustained (1 h) submaximal aerobic exercise in 9 clinically stable HTR [63 ± 10 yr of age, 24.2 ± 10.9 ml• kg ^-1 • min ^-1 peak O ₂ uptake (V _O2peak)] and 11 healthy age-matched controls (60 ± 11 yr of age and 36.3 ± 10.7 ml• kg ^-1 • min ^-1 V _O2peak for 6 RM controls and 35 ± 8 yr of age and 51.1 ± 10.4 ml• kg ^-1 • min ^-1 V _O2peak for5DM controls). Heart rate (HR) and left ventricular systolic and diastolic volumes (2-dimensional echocardiography) indexed to body surface area [end-systolic and end-diastolic volume indexes (EDVI and ESVI)], cardiac output (CI), ejection fraction (EF), systemic vascular resistance (SVRI), end-systolic elastance index, and arterial elastance index were determined. Although systolic function was maintained during incremental exercise, peak CI was significantly reduced (6.7 ± 2.4 vs. 11.6 ± 1.4 l• min ^-1 • m ^-2), secondary to blunted HR, EDVI, and increased peak SVRI, in HTR compared with DM controls. The lower peak CI in HTR than in RM controls was due to blunted peak EDVI (54.1 ± 13.2 vs. 68.6 ± 5.7 ml/m ²). During sustained submaximal exercise, HTR exhausted their preload reserve, a response for which changes in ESVI, HR, or EF did not fully compensate. Thus it appears that HTR are limited by impaired preload reserve, HR reserve, and vascular reserve during exercise conditions.