Heat syncope is primarily caused by which combination of factors?

Heat syncope is primarily caused by which combination of factors?

• A. Volume depletion alone
• B. Increased Metabolic Rate
• C. Volume depletion and peripheral vasodilation
• D. Hyperthermia-related vasoconstriction

Answer: (C)

Heat syncope happens when heat exposure triggers two main changes: loss of circulating fluid from sweating and reflex dilation of skin blood vessels to dissipate heat. The body opens up peripheral vessels to release heat, which lowers systemic vascular resistance. If you’re also volume-depleted from sweating or not drinking enough, the reduced blood volume means less blood returns to the heart (lower preload). Standing adds orthostatic stress, so venous return drops further, cardiac output falls, cerebral perfusion decreases, and you can momentarily lose consciousness. That combination of low volume and vasodilation is what drives heat syncope. Volume depletion alone misses the heat-driven vasodilation aspect; increased metabolic rate isn’t the key factor here, and heat-related vasoconstriction wouldn’t cause this scenario.

Heat syncope happens when heat exposure triggers two main changes: loss of circulating fluid from sweating and reflex dilation of skin blood vessels to dissipate heat. The body opens up peripheral vessels to release heat, which lowers systemic vascular resistance. If you’re also volume-depleted from sweating or not drinking enough, the reduced blood volume means less blood returns to the heart (lower preload). Standing adds orthostatic stress, so venous return drops further, cardiac output falls, cerebral perfusion decreases, and you can momentarily lose consciousness. That combination of low volume and vasodilation is what drives heat syncope. Volume depletion alone misses the heat-driven vasodilation aspect; increased metabolic rate isn’t the key factor here, and heat-related vasoconstriction wouldn’t cause this scenario.