Download 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