Info

ympathoadrenal \ \ '

— Metabolic vasodilation in muscles

Sympathetic vasoconstriction in viscera t Sympathoadrenal system \ Improved -.venous return

*Maximum cardiac rate can be estimated by subtracting your age from 220.

■ Skeletal muscle activity

Deeper breathing

■ Figure 14.20 Cardiovascular adaptations to exercise. These adaptations (1) increase the cardiac output, and thus the total blood flow; and (2) cause vasodilation in the exercising muscles, thereby diverting a higher proportion of the blood flow to those muscles.

Table I4.7 Cardiovascular Changes During Moderate Exercise

Variable

Change

Mechanisms

Cardiac output

Increased

Increased cardiac rate and stroke volume

Cardiac rate

Increased

Increased sympathetic nerve activity; decreased activity of the vagus nerve

Stroke volume

Increased

Increased myocardial contractility due to stimulation by sympathoadrenal system; decreased total peripheral resistance

Total peripheral resistance

Decreased

Vasodilation of arterioles in skeletal muscles (and in skin when thermoregulatory adjustments are needed)

Arterial blood pressure

Increased

Increased systolic and pulse pressure due primarily to increased cardiac output; diastolic pressure rises less

due to decreased total peripheral resistance

End-diastolic volume

Unchanged

Decreased filling time at high cardiac rates is compensated for by increased venous pressure, increased

activity of the skeletal muscle pump, and decreased intrathoracic pressure aiding the venous return

Blood flow to heart and muscles

Increased

Increased muscle metabolism produces intrinsic vasodilation; aided by increased cardiac output and increased

vascular resistance in visceral organs

Blood flow to visceral organs

Decreased

Vasoconstriction in digestive tract, liver, and kidneys due to sympathetic nerve stimulation

Blood flow to skin

Increased

Metabolic heat produced by exercising muscles produces reflex (involving hypothalamus) that reduces

sympathetic constriction of arteriovenous shunts and arterioles

Blood flow to brain

Unchanged

Autoregulation of cerebral vessels, which maintains constant cerebral blood flow despite increased arterial

blood pressure

Cardiac Output, Blood Flow, and Blood Pressure 427

of training. These adaptations enable the trained athlete to produce a larger proportionate increase in cardiac output and achieve a higher absolute cardiac output during exercise. This large cardiac output is the major factor in the improved oxygen delivery to skeletal muscles that occurs as a result of endurance training.

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