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Answer
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Answer: B) Decreased baroreceptor responsiveness
Clinical Breakdown
This elderly patient has two classic presentations:
- Orthostatic hypotension - BP drops from 130/88 (supine) to 100/70 (standing) = a 30 mmHg drop in systolic BP, which meets the diagnostic threshold (≥20 mmHg systolic drop on standing)
- Postprandial hypotension - dizziness after large meals
Both are explained by decreased baroreceptor responsiveness - the single unifying mechanism.
Pathophysiology
Baroreceptors (in the carotid sinus and aortic arch) are stretch-sensitive mechanoreceptors that detect changes in arterial pressure and trigger compensatory autonomic responses. Normally when you stand up:
- Venous blood pools in the lower limbs → venous return falls → BP drops momentarily
- Baroreceptors fire less → sympathetic outflow increases → heart rate rises + peripheral vasoconstriction → BP restored quickly
With aging, baroreceptor sensitivity declines due to:
- Reduced arterial wall compliance (stiffer vessels = less stretch-triggered firing)
- Blunted sympathetic reflex arcs
- Decreased adrenergic receptor responsiveness
The result: the compensatory reflex is too slow and inadequate, so BP stays low long enough to cause cerebral hypoperfusion and dizziness.
For postprandial hypotension: after a large meal, splanchnic blood pools in the gut (to aid digestion). Normally baroreceptors compensate for this redistribution. With impaired baroreceptor function, the BP drop after eating goes uncorrected.
Textbook confirmation: Barash Clinical Anesthesia states: "Elderly patients have age-related changes in cardiovascular physiology such as decreased sympathetic response to stress, reduced vascular compliance, impaired baroreceptor responses - placing them at risk for blood pressure lability and susceptibility to hypotension."
Why the Other Options Are Wrong
| Option | Why incorrect |
|---|---|
| A) Decreased vasovagal responsiveness | Vasovagal (vagus-mediated) responses cause bradycardia and hypotension (e.g., fainting from pain/emotion) - not orthostatic or postprandial hypotension. Decreased vasovagal tone would actually be protective. |
| C) Exaggerated Bezold-Jarisch reflex | BJR is a cardioinhibitory reflex triggered by ventricular mechanoreceptors (bradycardia + hypotension + vasodilation) - seen in inferior MI or contrast injection. Not the mechanism here. |
| D) Exaggerated Bainbridge reflex | The Bainbridge reflex causes tachycardia in response to increased right atrial filling pressure. This is the opposite direction of what's happening. |
The answer is B - the declining baroreceptor sensitivity in aging is the classic explanation for both orthostatic and postprandial hypotension in the elderly.
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