| Abstract: | Nóbrega, Antonio C. L., Jon W. Williamson, Jorge A. Garcia, and Jere H. Mitchell. Mechanisms for increasing stroke volume during static exercise with fixed heart rate in humans. J. Appl. Physiol. 83(3): 712-717, 1997. Ten patients with preserved inotropic function having adual-chamber (right atrium and right ventricle) pacemaker placed forcomplete heart block were studied. They performed static one-leggedknee extension at 20% of their maximal voluntary contraction for 5 minduring three conditions: 1)atrioventricular sensing and pacing mode normal increase in heart rate (HR; DDD)], 2) HRfixed at the resting value (DOO-Rest; 73 ± 3 beats/min), and3) HR fixed at peak exercise rate(DOO-Ex; 107 ± 4 beats/min). During control exercise (DDD mode),mean arterial pressure (MAP) increased by 25 mmHg with no change instroke volume (SV) or systemic vascular resistance. During DOO-Rest andDOO-Ex, MAP increased (+25 and +29 mmHg, respectively) because of aSV-dependent increase in cardiac output (+1.3 and +1.8 l/min,respectively). The increase in SV during DOO-Rest utilized acombination of increased contractility and the Frank-Starling mechanism(end-diastolic volume 118-136 ml). However, during DOO-Ex, agreater left ventricular contractility (end-systolic volume 55-38ml) mediated the increase in SV. |
