Heat acclimation expands plasma volume to improve thermoregulation. What is a direct consequence of plasma volume expansion during heat exposure?

Heat acclimation expands plasma volume to improve thermoregulation. What is a direct consequence of plasma volume expansion during heat exposure?

• A. Maintenance of stroke volume and improved thermoregulation during heat exposure.
• B. Decreased stroke volume and impaired thermoregulation.
• C. No change in heart function.
• D. Increased risk of dehydration with exercise.

Answer: (A)

Expanding plasma volume increases venous return to the heart, raising the preload. With greater preload, the heart can pump more blood per beat (maintained or increased stroke volume) during heat exposure, helping to keep cardiac output adequate without a large rise in heart rate. That preservation of stroke volume supports effective skin blood flow for heat dissipation and keeps thermoregulation functioning well. So the direct consequence is maintenance of stroke volume and improved thermoregulation during heat exposure. The other ideas don’t fit because plasma-volume expansion doesn’t cause a drop in stroke volume, it does not keep heart function unchanged, and it helps delay dehydration rather than increase its risk.

Expanding plasma volume increases venous return to the heart, raising the preload. With greater preload, the heart can pump more blood per beat (maintained or increased stroke volume) during heat exposure, helping to keep cardiac output adequate without a large rise in heart rate. That preservation of stroke volume supports effective skin blood flow for heat dissipation and keeps thermoregulation functioning well. So the direct consequence is maintenance of stroke volume and improved thermoregulation during heat exposure. The other ideas don’t fit because plasma-volume expansion doesn’t cause a drop in stroke volume, it does not keep heart function unchanged, and it helps delay dehydration rather than increase its risk.