CARDIOVASCULAR PHYSIOLOGY CONCEPTS
Fortunately, many of these drugs have rela-
tively short half-lives so that their effects
diminish within several hours.
Given that the ejection fraction is 20% and
the end-diastolic volume is 240 mL, the
stroke volume is 48 mL/beat using the fol-
lowing relationship: stroke volume = ejec-
tion fraction x end-diastolic volume. The
end-systolic volume is the end-diastolic vol-
ume minus the stroke volume, which equals
192 mL. The administration of a diuretic
would decrease the end-diastolic volume by
decreasing blood volume. The ACE inhibi-
tor, by reducing circulating angiotensin II
and aldosterone, would reinforce the effects
of the diuretic on the kidney and also cause
dilation of resistance and capacitance ves-
sels. These actions would further decrease
end-diastolic pressure by decreasing venous
pressure, and would reduce the afterload.
This latter effect enhances stroke volume
by decreasing the end-systolic volume and
increasing the cardiac output. The increased
stroke volume and decreased end-diastolic
volume would cause the ejection fraction
to increase. Although the ACE inhibitor
would decrease systemic vascular resistance,
the increased cardiac output might prevent
arterial pressure from falling, or at least
partially offset the pressure-lowering effect
of systemic vasodilation.
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