Page 9, O2 Uptake, Exercise & Cor. Circ., Dr. D. Penney


Exercise (continued..)

As well as oxygen consumption increasing during exercise or with an increased work rate, heart rate rises nearly 3-fold, and in an erect individual, stroke volume may increase by 35-50%, yielding a 4-5 fold increase in cardiac output (Figure 3.04). Increase in stroke volume is gained mainly through increases in inotropicity (especially in younger people), while Frank-Starling contributes little. See Misconception 8.

Systolic blood pressure rises, whereas diastolic and mean pressure may rise slightly or remain constant. At the same time, peripheral vasodilation, particularly in skeletal muscle, causes a drop in calculated peripheral vascular resistance, even though total flow has increased substantially. Finally, A-V 02 diff. increases as tissue 02 extraction rises. Stroke volume levels off or may even fall somewhat at high heart rates due to inadequate ventricular filling time.



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