Cardiovascular Function: Definition of Terms and Regulation
Cardiac output is the total blood volume pumped by ventricles per
minute (heart rate × stroke volume). Stroke volume is the blood pumped
by the left or right ventricle per beat; in a resting adult, it averages 60 to
80 mL of blood. Systole is the contraction phase of the cardiac cycle,
when ventricles pump stroke volumes. Diastole is the resting phase of
the cycle, which occurs between heartbeats. End-diastolic volume is the
blood volume in each ventricle at the end of diastole: 120 mL at rest. End-systolic volume is the blood volume in each ventricle after
contraction: 50 mL at rest. To maintain equal flow through pulmonary and
systemic circuits, the left and right ventricles maintain the same cardiac
output. The resting cardiac output is 4.8 to 6.4 L/min. Cardiac output increases
(20-85%) during intense exercise to transport more oxygen to muscles. This
greater blood flow is caused by higher blood pressure and arteriolar
vasodilation in muscles,
which is due to smooth muscle relaxation.
