A normal volunteer immerses one hand in ice-cold water for 60 seconds. Blood pressure rises significantly. What is the primary mechanism mediating this cold pressor response?

• A Direct cold-induced constriction of peripheral arteriolar smooth muscle
• B Pain-mediated activation of the sympathetic adrenergic vasoconstrictor outflow ✓
• C Withdrawal of parasympathetic vagal tone to the heart
• D Local axon reflex releasing calcitonin gene-related peptide

Explanation

The cold pressor response is driven by nociceptive pain from cold exposure, which activates central sympathetic outflow, increasing heart rate, cardiac output, and peripheral vasoconstriction. Option A is incorrect because the cold itself does not directly constrict vessels enough to raise systemic pressure. Option C describes a heart rate mechanism but not the dominant pressor pathway. Option D describes a vasodilator axon reflex, which would lower rather than raise blood pressure.

Reference: Ganong's Review of Medical Physiology, 26th ed.

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