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Sudden Dizziness on Standing: Orthostatic Hypotension Explained

Dizziness on standing (orthostatic intolerance) occurs when autonomic compensation for gravity fails.

Normal Physiology

  1. Stand → 500–1000 mL blood pools in legs/splanchnic bed
  2. Baroreceptors (carotid sinus, aortic arch) detect ↓ BP
  3. Sympathetic surge: ↑ HR, ↑ contractility, venoconstriction, arteriolar constriction
  4. BP maintained, cerebral perfusion preserved

Failure Mechanisms

  • Volume depletion: Dehydration, hemorrhage, diuretics, adrenal insufficiency
  • Autonomic neuropathy: Diabetes, Parkinson's, MSA, pure autonomic failure
  • Medications: Antihypertensives (α-blockers, diuretics, vasodilators), antidepressants, dopaminergic, PDE5 inhibitors
  • Prolonged bed rest/deconditioning
  • Age-related baroreflex decline

Diagnostic Criteria

SBP drop ≥20 mmHg or DBP ≥10 mmHg within 3 min of standing (or HUTT).

Management

  • Hydration (2–3 L/day), salt supplementation (if no HTN/HF)
  • Compression stockings (20–30 mmHg, waist-high)
  • Slow positional changes (sit → stand pause)
  • Review/med adjust offending drugs
  • Counter-maneuvers: leg crossing, squatting, fist clenching
  • Fludrocortisone, midodrine, droxidopa (refractory)

Red Flags

Syncope with injury, chest pain, palpitations, focal neuro signs, GI bleed → urgent eval.

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