Orthostatic Hypotension

Question 1

Definition of Orthostatic Hypotension

Answer 1

• Orthostatic hypotension is defined as a fall in systolic BP of at least 20mmHg (at least 30mmHg in patients with hypertension) and/or a fall in diastolic BP of at least 10mmHg within 3 minutes of standing.

Question 2

Aetiology of Orthostatic Hypotension

Answer 2

• Most commonly triggered by medications (i.e. alpha-blockers for treating BPH, diuretics, TCAs and antihypertensives)
• Diabetes mellitus
• Parkinson’s Disease
• Pure autonomic failure
• Multiple system atrophy

Question 3

Signs and Symptoms of Orthostatic Hypotension

Answer 3

• Signs/symptoms include postural light-headedness, syncope, parkinsonian features, cerebellar ataxia, weight loss, resting tachycardia or impaired HR, abnormal GI motility, erectile dysfunction, anhidrosis, heat intolerance, dry skin and focal hyperhidrosis.
• Risk factors include frailty, physical deconditioning, medications that impair sympathetic tone, volume depletion, autonomic neuropathy (i.e. diabetes mellitus), Parkinson’s Disease, Lewy body dementia and multiple system atrophy.

Question 4

Pathophysiology of Orthostatic Hypotension

Answer 4

• When standing, around 700ml of blood pools in leg and lower abdominal veins.
• As venous return decreases, resulting in a transient decline in cardiac output, baroreflex-mediated sympathetic activation with an increase in stroke volume and peripheral vasoconstriction as well as a parasympathetic withdrawal with an increase in HR prevents BP from falling.
• Failure of these mechanisms leads to orthostatic hypotension.

Question 5

Investigation of Orthostatic Hypotension

Answer 5

• Posture test
  
  • SBP falls >20mmHg (>30mmHg in patients with HTN) and DBP falls >10mmHg within 3 minutes of standing upright