Regulation of cardiac output during upright exercise in patients with aortic regurgitation

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Abstract
The change in cardiac output during upright exercise in patients with aortic regurgitation (AR) is not well known. We measured left ventricular (LV) ejection fraction (EF) and volume, regurgitant fraction (RF), total cardiac output and forward cardiac output at rest, and peak upright exercise by means of radionuclide angiography in ten normal subjects and 15 patients with AR. In the normal subjects, there was no significant change in the end-diastolic volume but there was a significant decrease in the end-systolic volume (p = 0.0001) and a significant increase in EF (p = 0.0001). The increase in cardiac output during exercise was due to increases in both stroke volume and heart rate. In patients with AR, there was a significant decrease during exercise in RF (53 ± 15% at rest, and 45 ± 15% during exercise; p = 0.03), and in end-diastolic and endsystolic volume (p = 0.02, and p = 0.003, respectively). The EF increased during exercise (p = 0.003). The total stroke volume did not change (68 ± 19 ml/m2 at rest, and 67 ± 14 ml/m2 during exercise; p, NS). Thus, in patients with AR, individual changes in EF, RF, and volume are quite variable, but as a group a decrease in RF and an increase in heart rate contribute to the increase in forward flow. The total stroke volume may not increase during exercise, despite an increase in EF and a decrease in end-systolic volume because of a concomitant decrease in end-diastolic volume.