During heat exposure, dehydration affects cardiovascular responses by which statement?

• A. Reduces plasma volume, lowering stroke volume and skin blood flow, increases heart rate to maintain cardiac output, and reduces sweat rate over time.
• B. Increases plasma volume and stroke volume, reducing heart rate.
• C. Has no effect on sweating rate.
• D. Increases skin blood flow to preserve heat loss.

Answer: (A)

During heat exposure, maintaining cooling relies on enough circulating volume to support skin blood flow and sweating. When dehydration lowers plasma volume, venous return to the heart falls, so the amount of blood the heart can pump with each beat (stroke volume) decreases. To keep cardiac output (CO = heart rate × stroke volume) from dropping, the heart rate increases. At the same time, reduced circulating volume and vascular adjustments to preserve central blood or overall dehydration effects lead to less skin blood flow. Sweat production also declines over time because there’s less extracellular fluid available to supply sweat glands and the body conserves water. So the overall pattern is lower plasma volume, reduced stroke volume and skin perfusion, compensatory higher heart rate to sustain CO, and a progressive reduction in sweat rate.