A 65-year-old man is brought to the emergency department with chest pain that he noticed after climbing a set of stairs. The emergency physician sends him for an exercise stress test. Which of the following physiologic mechanisms does the heart use to deal with increased work demand during an exercise stress test?
A) Decreased coronary artery diameter
B) Decreased metabolite production
C) Decreased oxygen extraction
D) Increased coronary blood flow
E) Increased oxygen extraction
First Aid Q&A for Step1 [2nd edition]©
[expand title=”CLICK HERE VIEW CORRECT ANSWER:”][sociallocker]The correct answer is D. An increase in myocardial contractility due to exercise leads to increased oxygen demand by the cardiac muscle and increased oxygen consumption, causing local hypoxia. This local hypoxia causes vasodilation of the coronary arterioles, which then produces a compensatory increase in coronary blood flow and oxygen delivery to meet the demands of the cardiac muscle. Oxygen extraction from heart muscle is maximized. Increased demand can be met only by increasing blood flow.[/sociallocker][/expand]