6. Regulation of cardiac pumping Flashcards
Isometric contraction
increase in tension in elastic elements first without a shortening of the muscle
Isotonic contraction
When tension in muscle is high enough to match the load, muscle shortens without further increase in tension
3 Factors affecting stroke volume
1) Preload 2)Contractility 3)Afterload
Preload
degree of stretch in the ventricles due to EDP which is due to EDV
Contractility
Changes in SV without changes in preload
Afterload
Changes in mean arterial blood pressure (MAP)
Preload Starling’s law of the heart
Increased EDV stretches myocytes
Myocytes respond at next beat with bigger force contraction
Matches VR to SV
Starling’s law of the heart: underlying mechanism of length/force relationship
In an almost empty chamber actin and actin overlap
Reduced ability to contract
In a full ventricle there is an optimum number of cross bridges available
Increased affinity of Troponin C to Ca2+
In an overfull heart (heart failure) actin and myosin are physically separated preventing them from interacting
Frank-Starling curve
law of Laplace
T = P x r / W
T Ventricular wall Tension
P Left ventricular Pressure (distending pressure; EDP)
r radius
W Wall thickness
Pressure-volume loops
- Atrial systole
- Isovolumic ventricular contraction
- Rapid ventricular ejection
- Reduced ventricular ejection
- Isovolumic ventricular relaxation
- Rapid ventricular filling
- Reduced ventricular filling
A = Mitral valve Closes
B = Aortic valve Opens
C = Aortic valve Closes
D = Mitral valve Opens
Effects of increasing preload on PV loop
EDV ↑by 30ml (A to B)
SV ↑by 30ml
ejection fraction ↑ from 60-67%
Effects of increasing afterload on PV loop
aortic pressure increases (A to B)
SV falls (B to C)
ejection fraction decreases from 60 to 40%
Effects of increasing contractility on PV loop
ESPVR shifts to left
SV increases
ESV falls
ejection fraction increases from 60-73%
Haemorrhage
↓ VR
↓ EDV
↓ SV
Sympathetic response (+ve inotropic)
↓filling time with large tachycardia
