What causes orthostatic hypertension?

Causes of Orthostatic Hypotension

Orthostatic hypotension is primarily caused by autonomic dysfunction leading to inadequate increase in peripheral vascular resistance and heart rate upon standing, resulting in blood pooling and decreased venous return. 1

Definition

• Orthostatic hypotension is defined as a reduction of systolic blood pressure ≥20 mmHg or diastolic blood pressure ≥10 mmHg within 3 minutes of standing 1
• In patients with supine hypertension, a systolic BP drop ≥30 mmHg should be considered diagnostic 1

Pathophysiological Mechanisms

• Autonomic Dysfunction:
  • Impaired increase in total peripheral resistance is the key mechanism 1
  • Degeneration of autonomic nuclei in the central nervous system and/or peripheral autonomic denervation 1
  • Dysfunction in the afferent pathway from arterial baroreceptors to the vasomotor center in the medulla oblongata 1
  • Dysfunction in the efferent pathway regulating vascular tone and heart rate 1

Primary Causes

Neurogenic Causes

• Primary autonomic failure conditions:
  • Parkinson's disease 2, 3
  • Multiple system atrophy 2, 3
  • Pure autonomic failure 2, 3
• Diabetic autonomic neuropathy 2, 3
• Neurodegenerative disorders affecting autonomic function 2

Medication-Induced

• Antihypertensive medications:
  • Diuretics (through volume depletion) 2, 4
  • Vasodilators 4, 5
  • Alpha-blockers (especially first dose) 4, 5
  • Centrally acting antihypertensive drugs 5
• Psychiatric medications:
  • Tricyclic antidepressants 4, 5
  • Phenothiazines 5
  • Monoamine oxidase inhibitors 6, 5
• Other medications:
  • Antiparkinsonian medications 4
  • Nitrates 4
  • Cardiac glycosides (can enhance bradycardia) 6

Volume Depletion

• Dehydration 4
• Bleeding 5
• Excessive diuresis 5

Contributing Factors

Age-Related Factors

• Frailty 1, 4
• Decreased baroreceptor sensitivity with aging 4
• Reduced cardiac compliance and stiff large arteries 4

Other Factors

• Prolonged bed rest or deconditioning 4, 7
• Alcohol consumption 4
• Heart failure with reduced ejection fraction 4, 7
• Comorbidities that affect autonomic function 1

Types of Orthostatic Hypotension

1. Classical OH:

   • Occurs within 3 minutes of standing
   • Due to impaired peripheral resistance increase and blood pooling 1
   • Common in frailty, medication use, autonomic failure, hypovolemia 1

2. Initial OH:

   • Occurs within 15 seconds of standing
   • Due to transient mismatch between cardiac output and peripheral resistance 1
   • More common in young, asthenic subjects; also in elderly with alpha-blocker use 1

3. Delayed OH:

   • Occurs after 3 minutes of standing
   • Pathophysiology uncertain; likely due to progressive fall in venous return 1
   • Associated with frailty, incipient autonomic failure, medications 1

Clinical Implications

• Increased mortality and cardiovascular disease risk 1, 7
• Increased risk of falls and fractures in elderly 4, 7
• Symptoms include dizziness, lightheadedness, fatigue, weakness, visual disturbances 1
• Can progress to syncope in severe cases 1, 7

Diagnostic Considerations

• Orthostatic hypotension is often associated with supine hypertension, complicating treatment 2, 3
• Heart rate increase is blunted in neurogenic OH (usually <10 bpm) 1
• Heart rate increase is preserved or enhanced in OH due to hypovolemia 1

Understanding these mechanisms is crucial for appropriate management strategies that focus on improving symptoms and quality of life while balancing the risk of worsening supine hypertension 2, 7.