Pathophysiology
Clinical meaning
Orthostatic hypotension (OH) is defined as a sustained drop in systolic blood pressure of 20 mmHg or more, or diastolic blood pressure of 10 mmHg or more, within 3 minutes of standing from a supine or seated position. When a person stands, approximately 500-1000 mL of blood pools in the lower extremities and splanchnic vasculature due to gravity. Normally, baroreceptors in the carotid sinus and aortic arch detect the decreased venous return and reduced stroke volume, triggering a compensatory response: increased sympathetic outflow causing arteriolar vasoconstriction and venous tone, increased heart rate and contractility, and release of catecholamines. In orthostatic hypotension, this compensatory mechanism fails. Causes include hypovolemia (dehydration, hemorrhage), medications (antihypertensives, diuretics, alpha-blockers, nitrates, antidepressants), autonomic dysfunction (diabetic neuropathy, Parkinson disease, pure autonomic failure, multiple system atrophy), prolonged bed rest (deconditioning of baroreceptor reflexes), and aging (decreased baroreceptor sensitivity, reduced plasma volume). Symptoms result from cerebral hypoperfusion: dizziness, lightheadedness, blurred vision, weakness, and syncope. Falls are the most significant clinical consequence, particularly in the elderly. The practical nurse measures orthostatic vital signs, implements fall prevention strategies, and reports findings.