Indices of contractility, regulation of ionotropy, matching of VR and CO

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Colorado State University
Biomedical Science
BMS 420
Charles Miller

1 October Increase preload → higher velocity of shortening for given afterload At higher afterloads, velocity of shortening decreases Isometric contraction when velocity = 0 (high afterload) V maxis velocity of shortening at theoretical 0 load Indices of Contractility Ejection fraction dP/dt Pressure-volume curves End-systolic pressure volume relation Increased contractility increases stroke volume. Increased pre-load increases stroke volume. Increased afterload decreases stroke volume. Increased circulating epinephrine → ↑ heart rate, ↑ contractility Increased sympathetic nerve activity or decreased parasympathetic nerve activity → ↑ heart rate, ↑ contractility Increased ventricular end-diastolic volume (Frank-Starling law) → ↑ stroke volume Increased contractility → ↑ stroke volume Increased heart rate/increased stroke volume → ↑ cardiac output Regulation of Inotropy (Ca )++ ++ ++ Phosphorylation of L-type Ca channels via Gs protein enhances permeability to Ca (due to activation of β adrenergic receptors by epi/NE). Ach activates Gi proteins → negative in
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