Cardiovascular System MCAT Practice Question
A 24-year-old male competitive runner presents to the sports medicine clinic for a pre-season cardiovascular evaluation. During maximal treadmill exercise testing, his heart rate increases from 70 bpm at rest to 180 bpm at peak exercise. Cardiac output increases from 5 L/min to 35 L/min. Echocardiography during submaximal exercise reveals increased left ventricular end-diastolic volume and enhanced myocardial contractility with a shortened ejection time. Which of the following mechanisms best explains the increase in stroke volume during maximal exercise in this athlete?
Answer choices
- AIncreased parasympathetic tone prolonging ventricular filling time and augmenting preload
- BVenoconstriction reducing venous capacity and increasing central venous pressure
- CSympathetic-mediated enhanced contractility combined with increased venous return from skeletal muscle contractionCorrect answer
- DDecreased afterload from systemic vasodilation with compensatory increase in contractility to maintain ejection fraction
- EIncreased preload from fluid shifts into the vasculature due to increased capillary hydrostatic pressure
- FProlonged diastolic filling time from reflex bradycardia during sustained exercise
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