16 - 20 Physiology SBAs for the Primary FRCA
Question 16
You are teaching an enthusiastic group of foundation year doctors about the physiology of the cardiac cycle.
Which of the following statements is true?
- The volume of blood ejected from the ventricle is called the end-diastolic volume
- During isovolumetric contraction the aortic valve is open
- During isovolumetric relaxation the aortic valve is open
- Both ventricles have the same shape pressure-volume morphology
- The dicrotic notch represents mitral valve closure
Answer
- Both ventricles have the same shape pressure-volume morphology
But the pressures are substantially higher in the left ventricle.
The end-diastolic volume is the volume of blood in the ventricle as the end of the filling phase. The percentage of this that is then ejected from the ventricle is the ejection fraction.
During isovolumetric anything, no fluid is moving anywhere, and all valves are closed - that's what makes it isovolumetric.
Isovolumetric contraction is the period of time where the ventricle has started to contract but hasn't yet exceeded the pressure on the other side of the valve, so it hasn't opened yet.
Likewise for relaxation - the ventricular pressure hasn't yet dropped low enough to open the mitral/tricuspid valve.
The dicrotic notch sort of represents aortic valve closure, but in reality it's a bit more complex than that.