A 28-year-old man with complete spinal cord transection at T4 develops pounding headache, profuse sweating above the level of the lesion, marked hypertension, and bradycardia during urinary catheterization. The bradycardia occurs because:

• A Massive sympathetic discharge reaches the heart directly
• B Intact vagal nuclei above the lesion respond reflexly to the hypertension ✓
• C The injured cord releases endogenous opioids that depress the sinoatrial node
• D Parasympathetic pelvic nerves are stimulated by the catheter

Explanation

This is autonomic dysreflexia: a noxious stimulus below a lesion above roughly T6 triggers unopposed sympathetic vasoconstriction, raising blood pressure severely. The baroreceptors and vagal outflow lie above the transection and remain intact, so the intact medulla mounts a brisk reflex bradycardia, though it cannot reverse the vasospasm below the lesion. Pelvic parasympathetic stimulation would cause erection and voiding, not bradycardia, eliminating option D.

Reference: Guyton and Hall Textbook of Medical Physiology, 14th ed.

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Written and medically reviewed by the StethoPrep medical team.