PHSI 208 Lecture Notes - Lecture 21: Vascular Resistance, Stroke Volume, Skeletal Muscle
Document Summary
During exercise, hr can be increased by over 100% whereas stroke volume can only be increased by ~50%. Changing the hr alone can have an inverse effect on sv because the ventricular filling time is decreased as the diastolic period decreases. Under normal physiological conditions, percentage of increase in co is generally more than that of hr during exercise. It is due to: positive inotropic effect to the contractile myocytes primarily caused by the increase of sympathetic activity. Ne & epi are potent b1 agonist (increase force of ventricular contraction: reduction in peripheral vascular resistance, compressing action of the contracting skeletal muscles (skeletal muscle pump) together with the venous valves to enhance the venous return. Reduction in peripheral vascular resistance: sympathetic stimulation during exercise produces vasoconstriction to all the vessels, including the contracting muscles (give rise to transient ischemia) Production of ne & epi (potent a-adrenergic agonist) during exercise cause vasoconstriction: followed by vasodilatation.
