What causes orthostatic hypotension?

Causes of Orthostatic Hypotension

Orthostatic hypotension is primarily caused by medication effects, autonomic dysfunction, volume depletion, and age-related changes in compensatory mechanisms that regulate blood pressure during positional changes. 1

Definition and Classification

• Orthostatic hypotension (OH) is defined as a decrease in systolic blood pressure ≥20 mmHg, diastolic blood pressure ≥10 mmHg, or a sustained decrease in systolic BP to an absolute value <90 mmHg within 3 minutes of standing or head-up tilt of at least 60 degrees 2
• In patients with supine hypertension, a systolic BP drop ≥30 mmHg should be considered diagnostic 2
• OH can be classified into several types based on timing and mechanism:
  • Classical OH: occurs within 3 minutes of standing 2
  • Initial OH: occurs within 15 seconds with rapid spontaneous recovery 2
  • Delayed OH: occurs beyond 3 minutes of standing 2

Primary Causes

Medication-Induced OH

• Medications are the most frequent cause of orthostatic hypotension 1, 3
• Common culprit medications include:
  • Diuretics (causing volume depletion) 1, 3
  • Vasodilators 3
  • Alpha-adrenoreceptor antagonists 3
  • Psychotropic drugs 3
  • Cardiovascular medications (responsible for almost half of syncope episodes in elderly) 4

Autonomic Dysfunction

• Primary autonomic failure conditions:
  • Parkinson's disease 1, 4
  • Multiple system atrophy 1, 5
  • Pure autonomic failure 5
• Secondary autonomic dysfunction:
  • Diabetic autonomic neuropathy 1, 6
  • Other peripheral neuropathies 7
  • Central nervous system diseases 7

Volume Depletion

• Hypovolemia from various causes:
  • Dehydration 8
  • Blood loss 8
  • Excessive diuresis 1
  • Prolonged vomiting or diarrhea 6

Age-Related Factors

• Impaired baroreflexes in elderly patients 5
• Delayed compensatory responses to positional changes 4
• Age-related changes in vascular compliance 6
• Reduced central blood volume 2

Pathophysiological Mechanisms

• Normal orthostatic BP regulation depends on:
  • Intact baroreflexes 5
  • Adequate blood volume 5
  • Effective defense against venous pooling 5
• In neurogenic OH, orthostatic heart rate increase is blunted (usually <10 beats per minute) due to impaired autonomic control 2
• In non-neurogenic OH (e.g., hypovolemia), orthostatic heart rate increase is preserved or enhanced 2
• Delayed OH may lead to progressive decrease in BP that can trigger reflex syncope 2

Other Contributing Factors

• Alcohol consumption (through direct CNS effects and volume depletion) 3
• Post-prandial state (blood pooling in splanchnic circulation) 3
• Prolonged bed rest causing deconditioning 3
• Excessive heat exposure causing vasodilation 6
• Endocrine disorders (adrenal insufficiency, hypothyroidism) 8

Clinical Significance

• OH is associated with increased mortality and cardiovascular disease prevalence 2
• Prevalence ranges from 6% in community-dwelling elderly to 33% in elderly hospital inpatients 1
• OH accounts for 20-30% of syncope cases in older adults 1
• Increases risk of falls, especially backward falls in elderly patients 4
• Impaired recovery after initial BP drop represents a negative prognostic factor in elderly 2

Diagnostic Considerations

• Testing should include BP measurements after 5 minutes of sitting/lying and then at 1 and 3 minutes after standing 3
• Assessment of medication history is crucial 1
• Evaluation of volume status is important 1
• Neurological examination for signs of autonomic dysfunction may be necessary 1
• Head-up tilt-table testing can be useful when standard orthostatic vital signs are nondiagnostic 8

Understanding the specific cause of orthostatic hypotension is essential for appropriate management, which should focus on symptom reduction and improving quality of life rather than normalizing blood pressure 3, 5.