1.1.4 Inotropy Flashcards
What happens if systolic function of cardiac muscle is compromised?
Stroke volume is inadequate and cardiac output falls
What happens if diastolic function of cardiac muscle is compromised?
Filling of the heart is compromised so decreased cardiac output
Ejection Fraction =
EF = SV / EDV (x 100)
How is SV regulated extrinsically?
Neuronally: ↑activity of symopathetic nevers to heart = ↑SV
Hormonally:
↑Blood plasma epinephrine = ↑SV
How is SV regulated intrinsically?
Mechanically:
↑Ventricular EDV (preload) = ↑SV
CO = ?
CO = SV x HR
MAP = ?
MAP = CO x TPR
How is free Ca2+ regulated in cardiac myocytes?
Voltage sensitive Ca2+ channels
Ca2+ SR stores
Na+/Ca2+ exchange
(↑Ca2+ at systole)
What causes cardiac muscle to contract?
Action potential
↑Ca2+ (voltage channels, SR)
Troponin C + Ca2+ = contraction
What makes cardiac muscle relax?
NCX channel removes Ca2+
ATP dependant pumps remove Ca2+ into SR
Define contractility
The strength of contraction at any given EDV.
What is a positive inotrope?
Increases heart rate
What is a negative inotrope?
Decreases heart rate
What is Ejection Fraction?
This is the the ratio of the blood ejected from the heart (SV) compared to the capacity of blood in the heart at diastole (EDV).
> 50% in a healthy heart
What are the different means by which the sympathetic system can increase contractility?
- Alter length-tension relationship of the heart muscle (preload)
- Change the cytosolic free Ca2+ conc
- Change the sensitivity of the myocardial contractile proteins to Ca2+
