Question

Figure shows four points on the pressure–volume diagram of a left ventricle. For each of the descriptions a–e below, select the best option from the following list of points and lines.

1. D

2. C

3. A

4. B

5. DC

6. DA

7. AB

8. CB

9. CD

10. AD

11. BA

12. BC

13. ABCD

14. DCBA

15. DCAB

16. ADCB

a. The beginning of diastole.

b. The end of systole.

c. Isometric contraction.

d. The segment between two points where the trace would depart maximally from a straight line.

e. One cardiac cycle starting with the onset of diastolic filling.

Answer 1

a. Option 1 D. At the beginning of diastole ventricular volume is around 50 ml and the pressure is around 120 mmHg (above atmospheric) because the isometric phase of diastole has not yet occurred.

b. Option 1 D. At the end of systole, ventricular volume has returned to 50 ml and the pressure is around 120 mmHg, having fallen from a maximal value around 140 mmHg as the aortic valve closes.

c. Option 12 BC. By definition volume is unchanged during isometric contraction, while pressure rises from about zero to a level which will open the aortic valve at arterial diastolic pressure, around 90 mmHg; thus isometric contraction is represented by the vertical line BC.

d. Option 9 CD. The two segments BC and DA represent isometric systole and isometric diastole, so are completely straight. During ventricular filling, AB, there is a small (around 5 mmHg) rise in pressure during atrial systole. In contrast, during the ejection phase of ventricular systole, CD, the pressure rises from arterial diastolic to arterial systolic (from around 90 to 140 mmHg) and then falls back to around 120 mmHg as the aortic valve closes.

e. Option 13 ABCD. Diastolic filling starts when ventricular volume is around 50 ml and its pressure close to atmospheric. The pressure–volume trace then moves to B where filling is complete, and continues in an anti-clockwise direction.