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Afterload

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General
Factors affecting intraventricular pressure
Systemic Vascular Resistance
Pulmonary Vascular Resistance

General
-ventricular wall tension during systole
-arterial impedance to ejection

wall tension = pressure the ventricle must overcome in order to reduce the ventricular cavity
LaPlace’s Law = helps describe wall tension = (intraventricular pressure)(ventricular radius)/ 2 (wall tension)

increased wall tension: larger ventricular radius ex. dilated left ventricle
decreased wall tension: increased wall thickness ex. left ventricular hypertrophy

Factors affecting intraventricular pressure
-force of ventricular contraction
-viscoelastic properties of aortal proximal branches
-viscosity and density of blood
-systemic vascular resistance

Systemic Vascular Resistance
-clinical equivalent of the left ventricular afterload
-primarily determined by the arterial tone

SVR = [(MAP – CVP)/ CO] x 80
SVRI= SVR x BSA
normal SVR: 900 – 1500 dynes-sec-cm-5

Pulmonary Vascular Resistance
PVR = [(PAP – LAP)/CO] x 80
normal PVR: 50 – 150 dynes-sec-cm-5