PERSISTENT EXERCISE INTOLERANCE FOLLOWING CARDIAC TRANSPLANTATION DESPITE NORMAL OXYGEN-TRANSPORT

To define the respective roles of the periphery and central oxygen tra nsport in the exercise limitation of heart transplanted patients (HTR) , we compared 11 HTR (15.1 +/- 10.8 months after transplantation) to s ix age and weight matched normal controls (C), during an incremental e xercise 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), wher eas the HTR all reached 90 W, with a significantly lower oxygen uptake (V over dot O-2), cardiac index (CI) and arterio-venous oxygen differ ence (AVO(2)D) values (respectively V over dot O-2: 16.6 +/- 2.6 vs 30 .0 +/- 9.3 ml . min(-1) . kg(-1) STPD; CI: 6.84 +/- 1.10 vs 10.55 +/- 2.86 l . min(-1) . m(-2); AVO(2)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 = NS). At the 90 W step whic h corresponds to the peak level that all the HTR reached, the C were c lose to their anaerobic threshold and showed similar parameters of oxy gen transport (V over dot O-2: 174 +/- 2.0; CI: 7.50 +/- 0.41; AVO(2)D : 90 +/- 10) but a lower lactate level (LA: 2.93 +/- 4.76; p < 0.002). At the same intermediate exercise levels V over dot O-2, CI and AVO(2 )D were similar in both groups, while the closely matched LA and venti lation increased faster in HTR, reaching significantly higher levels a s soon at the 30 W step. This evidence for an increased anaerobic exer cise energy generation in HTR suggests that the periphery participates significantly in their exercise limitation, a phenomenon that might b e improvable by retraining. Values: means +/- standard deviation.