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Effect of combined parasympathetic and sympathetic blockade on left ventricular relaxation at rest and during exercise in trained and untrained men.

We investigated the influence of autonomic blockade (AB) on the left ventricular (LV) diastolic function at rest (R) and during bicycle exercise (EX) in eight endurance-trained (TR) and ten untrained subjects (UT). Two-dimensional and M-mode echocardiography at the parasternal long axis were performed at rest and during an exercise protocol, which consisted of two stages of 50 and 100 W. Using the digitized data from the M-mode echocardiogram, the normalized maximal increase in LV dimension during the rapid filling phase (nmD) was calculated according to Hörtnagl. Additionally the ECG was recorded at R and during Ex 60 min after this first test. 0.02 mg.kg body mass-1 propanolol and 0.04 mg.kg body mass-1 atropine were injected intravenously over a 5-min period and the test procedure was repeated as described above. Before AB nmD increased significantly from resting values to 100 W in both groups, whereas nmD tended to be lower in UT compared to TR. During AB nmD of UT was rather unchanged at R and during EX compared to pre-blockade conditions. In contrast nmD of TR was slightly reduced and this difference was significant at 100 W. No major difference in nmD between the TR and UT group could be observed during AB. Before and during AB HR of TR were significantly lower at rest, 50 and 100 W compared to UT. We conclude that the enhanced diastolic relaxation observed in endurance athletes seems to be due to a training-induced adaptation of the autonomic nervous system.