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basic
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| basic
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Systemic
vascular resistance is governed by vessel length, blood viscosity, and
the inverse of vessel diameter. Although on occasion blood viscosity may
be sufficiently elevated in clinical circumstances to affect blood pressure
(polycythemia, treatment of chronic renal failure patients with erythropoetin),
by far the most common cause of increased systemic vascular resistance
is decreased vessel diameter in response to pathology or elevated levels
of vaso-constrictive hormones. Such disorders are not common, but their
diagnosis is important because the hypertension is reversible with treatment
of the underlying condition (Note
1).
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| Note
1 |
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One
of the more frequent causes of reversible hypertension is sleep-apnea.
The mechanism of hypertension is not fully understood, but appears to be
related to increased systemic vascular resistance secondary to catecholamine
release. The release of catecholamines is stimulated by hypoxemia.
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