Cardiac Output: And Influencing Factors

Cardiac Output Amount of blood pumped out by each ventricle in 1 min CO = HR x SV

Cardiac Reserve The difference between resting and maximal CO

Stroke Volume SV = EDV – ESV –EDV (volume of blood in ventricle after diastole) –ESV (volume of blood remaining in ventricle after contraction) –With each beat, ~ 60% of blood in chambers is emptied

Frank-Starling law of the heart Preload = critical factor in determining SV

Preload Degree to which cardiac cells are stretched before contraction –Optimal length determined by: If max # of cross bridge attachments occur If max force of contraction occurs

Venous Return The volume of blood returning to heart and stretching ventricles If venous return increases, EDV increases; therefore SV increases Left and right ventricles have equal venous return; therefore blood does not “pool” or backflow in heart

Contractility Contractile strength of heart (due to increased CA 2+ ) Causes increased release of blood (therefore lower ESV)

Afterload Force to eject blood from ventricles Constant in healthy people; lower in people with hypertension (therefore increases ESV and decreases SV)