Cardiovascular drift: a progressive rise in heart rate as stroke volume falls.

• A. A rise in systolic blood pressure only
• B. A progressive rise in heart rate as stroke volume falls
• C. A decrease in heart rate
• D. No overall change in heart rate

Answer: (B)

Cardiovascular drift is the gradual increase in heart rate that occurs during prolonged, steady exercise as stroke volume falls. This happens because sweating reduces plasma volume, which lowers venous return to the heart and decreases end-diastolic volume, so each heartbeat pumps out less blood. At the same time, rising body temperature causes skin blood vessels to dilate, increasing the need for blood flow to the skin. To keep overall blood flow (cardiac output) from dropping, the heart rate must rise. So even though stroke volume declines, the total amount of blood pumped per minute stays roughly the same or increases slightly due to the higher heart rate. This pattern isn’t about a rise in systolic blood pressure alone, nor a decrease in heart rate, nor no overall change in heart rate, which is why it best describes cardiovascular drift.