Cardiovascular drift during prolonged exercise is best described by which statement?

• A. Stroke volume increases due to increased venous return
• B. Heart rate decreases to maintain cardiac output
• C. With rising core temperature, venous return falls and heart rate rises to maintain cardiac output
• D. Blood plasma increases

Answer: (C)

Cardiovascular drift describes the rise in heart rate that accompanies prolonged steady-state exercise, with a falling stroke volume. As exercise continues, especially in the heat, skin blood flow increases to dissipate heat, which reduces venous return to the heart. Sweating also lowers plasma volume, further decreasing venous return and end-diastolic filling, so stroke volume drops. To keep cardiac output (CO = HR × SV) from falling, heart rate rises. This explains why the statement says that with rising core temperature venous return falls and heart rate rises to maintain cardiac output.