Physiology Objectives 10



Physiology Objectives 10

1. 4 determinants of myocardial performance:

a. Preload

b. Afterload

c. Heart Rate

d. Contractility

2. Left ventricular ejection fraction: Stroke volume/End diastolic volume

• Note: Normal EF = 65%

3. Ventricular performance curve:

4. Preload affect on cardiac performance: increasing preload increase stroke volume, cardiac output and ventricular efficiency; this can be demonstrated on a PV loop as a shift of end diastolic volume to the right.

5. Factors affecting myocardial preload:

a. Blood volume: increased blood volume → increased preload

b. Venous tone: increased venous tone → increased preload

c. Ventricular distensibility: increased distensibility → increased preload

6. Afterload effect on cardiac performance: an increase in afterload will shift the PV loop to the right; if there is no corresponding increase in preload, this will cause a decrease in stroke volume. If there is a corresponding increase in preload, the effect is called the Bowditch effect

7. Factors affecting myocardial afterload:

a. Aortic stenosis/embolism: increased stenosis/embolisms → increased afterload

b. Hypertension: increased hypertension → increased afterload

c. Blood volume: increased blood volume → increased afterload

d. Vasoeffectors: vasoconstriction → increased afterload

8. Contractility effect on the PV loop: increased contractility will shift the active tension curve upward and increases stroke volume

9. Factors affecting myocardial contractility:

a. Heart rate: increased heart rate → increased contractility

b. Inotropic effects: positive inotropic effects → increased contractility

c. Autonomic control: sympathetic stimulation → increased contractility

d. Cardiac glycosides: cardiac glycoside use → increased contractility

10. Bowditch effect on cardiac performance: stroke volume stays constant; however, since both end diastolic and end systolic volumes increase, ejection fraction decreases (EF = SV/EDV)

11. Heart failure:

a. Forward heart failure: inability of heart to pump blood forward at a sufficient rate to meet metabolic demands

b. Backward heart failure: ability to pump sufficient blood only if cardiac filling pressures are abnormally high

12. Systolic dysfunction: impaired contractility, increased afterload (decrease in active tension curve in a PV loop)

Diastolic dysfunction: impaired ventricular filling (increase in passive tension curve in a PV loop)

• Note: 1/3 of dysfunction is diastolic and 2/3 is systolic

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