The cardiac function was studied by radionuclide cardiography in eight healthy subjects at rest and during submaximal upright exercise before and after autonomic blockade with metoprolol and atropine. At rest the median stroke volume was reduced by 21% during autonomic blockade (P<0.01), but cardiac output was maintained by a concomitant increase in heart rate. The systolic blood pressure was reduced from 120 to 105 mmHg (P<0.01), and left ventricular ejection fraction was reduced from 61 to 56% (P<0.05). After autonomic blockade the heart rate reached during exercise was the same. Stroke volume and cardiac output were maintained through cardiac dilation. The increase in left ventricular end-diastolic volume was 31 vs. 10% during control conditions (P<0.01). The systolic blood pressure was reduced from 174 to 135 mmHg (P<0.01). Left ventricular ejection fraction was reduced from 75 to 67% (P<0.05), but the increase from rest to exercise was preserved. Total peripheral resistance was reduced by 17% (P<0.05). These findings suggest that the heart possesses intrinsic mechanisms to maintain cardiac output during submaximal upright exercise. End-diastolic dilation results in a preserved stroke volume despite a reduced contractility.
|Number of pages||4|
|Journal||Journal of Applied Physiology|
|Publication status||Published - 1 Dec 1987|