College Answer

Many candidates lost marks for poor quality diagrams with inaccurate labelling. An accurate diagram was required. Many answers lacked sufficient detail regarding contractility and afterload.

Discussion

If a trainee had failed this question and were looking for an answer as to how and why they failed, the remark that "an accurate diagram was required" would be uninformative. This examiner comment in general leaves much to be desired. Fortunately, this SAQ was plagiarised verbatim from Question 12(p.2) from the first paper of 2008, and that time, the examiners did write something useful in their response. On the basis of their comments, it was possible to fashion this answer:

The following information can be obtained from this monstrosity: 

• Volumes:
  • End-diastolic volume (where the mitral valve opens)
  • End-systolic volume (where the aortic valve closes)
  • Stroke volume (the difference between the end-diastolic and end-systolic volumes)
  • Ejection fraction, which is the ratio of stroke volume to end-diastolic volume
• Pressures:
  • Systolic blood pressure (peak of the curve)
  • Diastolic blood pressure (where the aortic valve opens)
  • End-systolic blood pressure (where the aortic valve closes)
• Pressure-volume relationships:
  • Systolic ejection, which has fast and slow phases
  • Diastolic filling
  • Isovolumetric contraction and relaxation
  • The end-diastolic pressure-volume relationship (EDPVR), which describes ventricular elastance
  • The end-systolic pressure-volume relationship (ESPVR), which describes contractility
  • The effective arterial elastance line which connects the point of end-diastolic pressure and volume to the point of end-systolic volume, and which is an approximation of afterload
• Areas:
  • Total mechanical energy (stroke work),  which consists of:
    • Stroke work, which is the total area of the P-V loop 
    • Stored "potential" mechanical energy (in the LV wall), which is the area under the ESPVR line.