Describe the factors affecting left ventricular function
Candidates often misinterpreted the question and described determinants of cardiac output. The answer should have focussed on factors affecting/contributing to normal LV function - not pathological states. Some answers showed a lack of appreciation that normal left ventricular function is afterload independent, due to compensatory reflexes. Answers needed to consider intrinsic and extrinsic factors affecting LV function - the latter (e.g. SNS, PSNS, hormones, drugs) was often left out. Answers needed to consider both systolic and diastolic function. An excellent answer included physiological phenomena such as the Treppe effect, Anrep effect and baroreceptor and chemoreceptor reflexes. Mention of normal conduction and pacing as well as blood supply limited by diastole scored additional marks.
It is no wonder this question had such a low pass rate. What is remarkable is that 12% of the candidates somehow accidentally stumbled on the exact thing the examiners had in mind. Which would have been the only way they would have arrived there, because certainly a direct reading of the question does not betray anything of their expectations.
Judging by the college comments, what they really wanted was a discussion of the physiological influences which affect LV afterload ("appreciation that normal left ventricular function is afterload independent, due to compensatory reflexes"), LV preload ("blood supply limited by diastole") and LV contractility ("Treppe effect, Anrep effect"). These, interestingly, are also important determinants of cardiac output. However, it appears we would have to phrase the answer in a way which does not make any reference to the determinants of cardiac output. What follows is an attempt to carefully step around this issue by rewording some of the determinants. As the function of the LV mainly involves contracting and relaxing cyclically, "systolic" and "diastolic" seemed like reasonable headings.
Main influences on LV systolic function:
Main influences on LV diastolic function:
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