what is postural hypotension
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postural orthostatic hypotension definition causes pathophysiology
Harrison's Principles of Internal Medicine, Twenty First Edition
Page 6764
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orthostatic hypotension diagnosis symptoms management treatment
Harrison's Principles of Internal Medicine, Twenty First Edition
Page 707
GradeResponse
GradeResponse
Postural (Orthostatic) Hypotension
Postural hypotension — also called orthostatic hypotension (OH) — is defined as a drop in blood pressure upon standing up from a lying or sitting position.
Definition
A fall in:
- Systolic BP > 20 mmHg, OR
- Diastolic BP > 10 mmHg
...within 3 minutes of assuming an upright posture from a supine position.
(Harrison's Principles of Internal Medicine, 21st Ed., p. 6764)
Pathophysiology
When a person stands up:
- Gravity causes ~500–1000 mL of blood to pool in the lower extremities and splanchnic circulation.
- Normally, baroreceptors in the aortic arch and carotid sinus detect the drop in BP and trigger compensatory responses: increased heart rate, vasoconstriction, and increased cardiac output.
- In postural hypotension, this compensatory reflex fails — due to autonomic dysfunction, volume depletion, or medications — resulting in sustained low BP and reduced cerebral perfusion.
A lack of compensatory tachycardia when BP drops is a key sign of autonomic insufficiency, seen in conditions like diabetes mellitus and Parkinson's disease.
Causes
| Category | Examples |
|---|---|
| Autonomic dysfunction | Parkinson's disease, multiple system atrophy, diabetic neuropathy, pure autonomic failure |
| Volume depletion | Dehydration, hemorrhage, diarrhea, vomiting, excessive sweating |
| Medications | Antihypertensives, diuretics, nitrates, alpha-blockers, antidepressants (TCAs), antipsychotics, levodopa |
| Cardiac causes | Bradycardia, heart failure, aortic stenosis |
| Endocrine | Adrenal insufficiency (Addison's disease), hypothyroidism |
| Prolonged bed rest / deconditioning | Post-surgical patients, elderly individuals |
| Postprandial hypotension | After eating, especially in the elderly |
Symptoms
Symptoms arise from reduced perfusion to the brain and other organs (Harrison's, p. 707):
- Classic: Lightheadedness, dizziness, presyncope (near-fainting) upon standing
- Non-specific: Generalized weakness, fatigue, cognitive slowing, leg buckling
- Visual blurring — due to retinal or occipital lobe ischemia
- "Coat-hanger headache" — pain in the suboccipital, posterior cervical, and shoulder regions, likely from neck muscle ischemia
- Orthostatic dyspnea — breathlessness on standing, thought to reflect ventilation-perfusion mismatch
- In severe cases: syncope (fainting) and falls
Symptoms may also be absent, making routine assessment important.
Diagnosis
- Lying-to-standing BP measurement: Check BP after 5 min supine, then at 1 and 3 min after standing
- Tilt-table test: For cases where active standing is not feasible
- Blood tests: full blood count (anaemia), electrolytes, glucose, cortisol
- ECG: to exclude cardiac arrhythmias
- Review medications
Management
Non-pharmacological:
- Rise slowly from lying/sitting positions
- Increase fluid and salt intake (if not contraindicated)
- Wear compression stockings
- Elevate the head of the bed at night
- Avoid triggers: prolonged standing, hot environments, alcohol, large meals
- Regular physical exercise / reconditioning
Pharmacological:
- Fludrocortisone — mineralocorticoid; expands blood volume
- Midodrine — alpha-1 agonist; causes vasoconstriction
- Pyridostigmine — enhances ganglionic transmission
- Droxidopa — norepinephrine precursor (especially in neurogenic OH)
- Address underlying cause (e.g., stop offending medications, treat Parkinson's, correct dehydration)
Special Considerations
- Elderly patients are at highest risk due to impaired baroreflex sensitivity, polypharmacy, and reduced vascular stiffness.
- Neurogenic orthostatic hypotension (from autonomic nerve damage) is often accompanied by supine hypertension, making treatment a careful balancing act.
- Falls and fractures from postural hypotension are a major concern in elderly populations.
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