Respiratory System USMLE Step 1 Practice Question
A 42-year-old man undergoes cardiac catheterization for evaluation of chest pain. During the procedure, simultaneous blood samples are obtained from the radial artery and the coronary sinus (venous drainage of the heart). Analysis reveals an arterial CO2 content of 48 mL/100mL blood and a venous CO2 content of 52 mL/100mL blood. The patient's heart rate is 72 bpm and cardiac output is 5 L/min. Which of the following relationships best explains the venous-arterial CO2 content difference across the myocardium?
Answer choices
- AMyocardial oxygen consumption divided by coronary blood flow
- BCoronary blood flow divided by myocardial CO2 production
- CMyocardial CO2 production divided by coronary blood flowCorrect answer
- DMyocardial CO2 production divided by myocardial oxygen consumption
- EArterial PCO2 minus alveolar PCO2
- FAlveolar ventilation divided by total cardiac output
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