同济大学：《生理学》课程电子教案（PPT课件）05 Cardiac Muscle Mechanics

Long Duration Twitch in Cardiac Muscle Rapid inflow Diastasis Aortic vale 120 Aonic valve closes opens A-V valve A-V valv closes 20 0 50100 150 200 Time (msec)

Length-Force Relationship in Cardiac Muscle: The Starling -Frank Curve. Total Active Passive Length

How Does Linear Force in a Muscle Produce Pressure in a Ventricle Two Equivalent Curves: Isolated Muscle Heart Length Volume (pressure is directly proportional to the force produced by the cells)

"lsovolumetric contraction"=Isometric Force Generation. Aortic Valve Mitral Valve Both valves closed;Muscle is activated and generates force isometrically. The pressure rises.No blood is ejected yet.Therefore it is called"isovolumetric". The energy required to generate this pressure does "pressure work" Note:This represents the Left Ventricle

Ejection. Ventricular pressure exceeds aortic pressure:The Aortic valve opens;Muscle now shortens.Blood is ejected into the aorta. Work is now being done.This is referred toas“volume work

Varying Force in Cardiac Muscle: Contractility and the length-force(Starling)curve A B D C B A Length (Volume)

Contractility change in an isolated myocyte

Force-Velocity Relationship. 10 At a given velocity of shortening,the muscle exerts greater tension if we stretch it more with a greater preload. At a given afterload, Velocity of the velocity of shortening shortening is greater (mm/s) if we stretch the muscle more with a Short initial length greater preload. (lesser preload) Long initial length 0 (greater preload) 0 5 10 Load(g) The contraction is isometric at zero velocity

CONTRACTILITY Increased-- Decreased --- Afterload

Preload (Frank-Starling Relationship) Definition of preload:Amount of stretch imposed on the left ventricular muscle when the left ventricular chamber fills with blood during diastole Preload is defined as the amount of ventricular filling during diastole. Increasing Preload (ventricular muscle stretch)increases (a)the amount of pressure the ventricle can produce,and (b)the velocity of shortening during systole. Preload