The diving reflex, triggered by immersion of the face in cold water, results in which main protective effect?

The diving reflex, triggered by immersion of the face in cold water, results in which main protective effect?

• A. Bradycardia and slowed metabolic rate
• B. Tachycardia and increased metabolic rate
• C. Peripheral vasodilation and increased blood flow to limbs
• D. Increased respiratory rate and airway reflexes

Answer: (A)

Immersion of the face in cold water triggers a protective response that conserves oxygen by reducing the body's demand for it. The cold facial stimulus activates the trigeminal nerve, which then increases parasympathetic (vagal) output to the heart, causing bradycardia—slowing the heart rate. Slower heart rate directly lowers oxygen consumption by the heart and body. This bradycardia is the hallmark of the diving reflex, and it is complemented by a lowered metabolic demand, making oxygen last longer during submersion. Peripheral vasoconstriction also helps by redirecting blood toward the brain and heart, but the core protective effect described here is the drop in heart rate and overall metabolic demand. The other responses—tachycardia, peripheral vasodilation, or increased breathing rate—would increase oxygen use and are not protective in this context.

Immersion of the face in cold water triggers a protective response that conserves oxygen by reducing the body's demand for it. The cold facial stimulus activates the trigeminal nerve, which then increases parasympathetic (vagal) output to the heart, causing bradycardia—slowing the heart rate. Slower heart rate directly lowers oxygen consumption by the heart and body. This bradycardia is the hallmark of the diving reflex, and it is complemented by a lowered metabolic demand, making oxygen last longer during submersion. Peripheral vasoconstriction also helps by redirecting blood toward the brain and heart, but the core protective effect described here is the drop in heart rate and overall metabolic demand. The other responses—tachycardia, peripheral vasodilation, or increased breathing rate—would increase oxygen use and are not protective in this context.