What causes orthostatic hypotension?

Causes of Orthostatic Hypotension

Orthostatic hypotension is predominantly caused by medications, autonomic dysfunction, volume depletion, and age-related physiological changes, with specific etiologies varying between neurogenic and non-neurogenic forms. 1

Definition and Diagnostic Criteria

Orthostatic hypotension is defined as:

• A sustained decrease in systolic blood pressure ≥20 mmHg and/or diastolic blood pressure ≥10 mmHg within 3 minutes of standing from a supine position 1
• Or a sustained decrease in systolic BP to an absolute value <90 mmHg 1

Major Causes of Orthostatic Hypotension

Non-Neurogenic Causes

1. Medications:

   • Antihypertensives (especially alpha-1 blockers, first dose effect) 2
   • Diuretics (causing volume depletion) 3, 2
   • Vasodilators and nitrates 2
   • Psychiatric medications (phenothiazines, tricyclic antidepressants, MAOIs) 2
   • Dopamine agonists (including Parkinson's medications) 3, 2
   • Opioids 3

2. Volume Depletion:

   • Dehydration 4
   • Blood loss 4
   • Excessive diuresis 2
   • Inadequate fluid/salt intake 1

3. Age-Related Physiological Changes:

   • Reduced thirst sensation 3
   • Decreased baroreceptor sensitivity 3
   • Reduced ability to preserve sodium and water 3
   • Diminished heart rate response to orthostatic stress 3, 1

4. Cardiovascular Conditions:

   • Cardiac insufficiency 5
   • Impaired venous return 5
   • Venous pooling 6

Neurogenic Causes (Autonomic Dysfunction)

1. Neurodegenerative Disorders:

   • Parkinson's disease 1
   • Multiple system atrophy 1
   • Pure autonomic failure 1
   • Dementia with Lewy bodies 1

2. Peripheral Neuropathies:

   • Diabetic autonomic neuropathy 3, 1
   • Amyloidosis 1
   • Autoimmune autonomic neuropathy 1
   • Paraneoplastic autonomic neuropathy 1

3. Central Nervous System Disorders:

   • Stroke (damage to vasomotor centers in brainstem) 1
   • Spinal cord injuries 1

4. Other Autonomic Disorders:

   • Carotid sinus hypersensitivity (especially in elderly) 3
   • Postprandial hypotension 3

Prevalence and Risk Factors

• Prevalence varies from 6% in community-dwelling elderly to 33% in elderly hospital inpatients 3
• Orthostatic hypotension is an attributable cause of syncope in 20-30% of older patients 3
• Overall prevalence is approximately 20% in older adults and 5% in middle-aged adults 7
• Risk increases with:
  • Advanced age 1
  • Diabetes mellitus 7
  • Polypharmacy 3
  • Neurodegenerative diseases 1

Clinical Implications

• Associated with increased all-cause mortality (up to 50% increase in relative risk) 1, 7
• Increased risk of cardiovascular disease 1
• Higher risk of falls and injuries 7
• Significant impact on quality of life through symptoms like dizziness, lightheadedness, visual disturbances, weakness, fatigue, and syncope 1, 4

Clinical Pearls

• Supine hypertension often coexists with orthostatic hypotension in elderly patients, complicating treatment 3
• Heart rate response can help differentiate between neurogenic (minimal/absent compensatory heart rate increase) and non-neurogenic causes (preserved heart rate increase) 1
• Orthostatic hypotension may present atypically in the elderly as falls, gait disorders, or cognitive changes 3
• Up to 40% of elderly patients with syncope due to orthostatic hypotension may have complete amnesia for the event 3
• Delayed orthostatic hypotension (occurring after 3 minutes) may be missed with standard testing 1

Understanding these diverse causes is essential for proper diagnosis and management of orthostatic hypotension, with treatment approaches targeting the underlying etiology to improve patient outcomes and quality of life.