The baroreflex is the fastest blood pressure regulatory mechanism. In a patient with autonomic neuropathy (e.g., diabetic), the baroreflex gain is severely reduced. What clinical finding best demonstrates this defect?

• A Persistent hypertension at rest due to loss of vagal tone
• B Exaggerated blood pressure response to exercise
• C Orthostatic hypotension with absent compensatory tachycardia upon standing ✓
• D Loss of Cheyne-Stokes breathing during sleep

Explanation

The arterial baroreflex normally responds to the fall in blood pressure upon standing by: (1) increasing heart rate via reduced vagal tone and increased sympathetic tone, (2) increasing myocardial contractility, and (3) increasing peripheral vascular resistance. In autonomic neuropathy with impaired baroreflex, standing causes BP to fall (orthostatic hypotension, defined as ≥20 mmHg systolic or ≥10 mmHg diastolic drop) without compensatory tachycardia (heart rate increases < 10–15 bpm or remains fixed). This combination is pathognomonic of efferent autonomic failure.

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

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