During heat stress in exercise, which of the following best describes the cardiovascular response?

During heat stress in exercise, which of the following best describes the cardiovascular response?

• A. Increased skin blood flow for cooling; higher heart rate and cardiac output; venous return may be reduced by plasma volume loss.
• B. Decreased skin blood flow with reduced heart rate and cardiac output.
• C. No change in skin blood flow or heart rate during heat stress.
• D. Increased skin blood flow but decreased cardiac output due to fluid shifts.

Answer: (A)

When the body heats up during exercise, it boosts cooling by dilating the skin vessels, so more blood flows to the skin to lose heat. That increased skin blood flow is a hallmark of heat stress. To keep delivering blood to working muscles and maintain blood pressure despite the heat, heart rate rises and cardiac output increases. At the same time, sweating reduces plasma volume, which can lower venous return to the heart and limit filling of the heart between beats. The result is a scenario where skin blood flow is up for cooling, heart rate and cardiac output are up to meet demands, and venous return may be reduced by fluid loss. This combination best fits the described response.

When the body heats up during exercise, it boosts cooling by dilating the skin vessels, so more blood flows to the skin to lose heat. That increased skin blood flow is a hallmark of heat stress. To keep delivering blood to working muscles and maintain blood pressure despite the heat, heart rate rises and cardiac output increases. At the same time, sweating reduces plasma volume, which can lower venous return to the heart and limit filling of the heart between beats. The result is a scenario where skin blood flow is up for cooling, heart rate and cardiac output are up to meet demands, and venous return may be reduced by fluid loss. This combination best fits the described response.