How odd that a giraffe with its heart-to-head distance exceeding 2 meters does not find it difficult to maintain circulatory homeostasis in the upright position, whereas man with a mere 30 cm separating the two organs sometimes does. Physiologists have come closer to explaining the giraffe's circulatory agility1 than the homeostatic sluggishness of humans with orthostatic hypotension.
Failure to regulate blood pressure on assuming the upright position may be idiopathic or secondary to a known neurologic or systemic disease. It is much more common among diabetic patients than in the general population.
The increased prevalence of orthostatic hypotension in diabetics need not be too surprising. Autonomic neuropathy could well compromise baroreceptor reflexes in the carotid sinuses and aortic arch and chemoceptor reflexes in the carotid and aortic bodies. The plausibility of such a mechanism is supported by the frequency of associated peripheral neuropathy in these patients.
Plausibility, however, does
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