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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