Persistent Exercise Intolerance Following Cardiac Transplantation Despite Normal Oxygen Transport

To define the respective roles of the periphery and central oxygen transport in the exercise limitation of heart trainsplanted patients (HTR), we compared 11 HTR (15.1 ± 10.8 momths after transplantation) to six age and weight matched normal controls (C), during an incremental exercise test (30 W/3 min steps; supine position), up to peak exercise level. The C stopped between 120 and 240 W (mean = 180 ± 39 W), whereas the HTR all reached 90 W, with a significantly lower oxygen uptake (VO₂), cardiac index (Cl) and arterio-venous oxygen difference (AVO₂D) values (respectively VO₂: 16.6 ± 2.6 vs 30.0 ± 9.3 ml · min^-1 · kg^-1 STPD; Cl: 6.84 ± 1.10 vs 10.55 ± 2.861 min^-1 · m 2; AVO₂,D: 94 ± 13 vs 109 ± 9 ml · l^-1 ; all p < 0.05) but with similar lactate (LA) values (respectively 7.25 ± 1.98 vs 7.71 ± 1.55 mmol · l^-1; p = NIS). At the 90 W step which corresponds to the peak level that all the HTR reached, the C were close to their anaerobic threshold and showed similar parameters of oxygen transport (VO₂: 17.4 ± 2.0; Cl: 7.50 ± 0.41; AVO₂D: 90 ± 10) but a lower lactate level (LA: 2.93 ± 4.76; p< 0.002). At the same intermediate exercise levels VO₂, Cl and AVO₂D were similar in both groups, while the closely matched LA and ventilation increased faster in HTR, reaching significantly higher levels as soon at the 30 W step. This evidence for an increased anaerobic exercise energy generation in HTR suggests that the periphery participates significantly in their exercise limitation, a phenomenon that might be improvable by retraining. Values: means ± standard deviation.

Key words

Exercise - aerobic - heart transplantatiom - oxygen consumption - energy metabolism - cardiac output