Postural hypotension

Postural hypotension, also known as orthostatic hypotension, is clinically defined as ≥20 mmHg drop in systolic BP or at least 30 mmHg in hypertensive patients or ≥10 mmHg in diastolic BP within 3 minutes of standing from a seated position. It is predominantly a condition that affects the ageing population.

⚠️ Pathophysiology and risk factors

In a normal individual, when they stand, approximately 700ml of blood pools in the leg veins and abdominal veins. This results in the venous return of the heart decreasing transiently. This transiently reduces the cardiac output. This is detected by baroreceptors which detect a decrease in stretch of the vessels. This then triggers the baroreceptors reflex that activates the sympathetic nervous system to increase the stroke volume and activate peripheral vasoconstriction. These mechanisms prevent the blood pressure from dropping despite the redirection of blood that occurs with postural change.

A failure of these mechanisms results in orthostatic hypotension. Cerebral blood flow remains constant throughout a wide range of blood pressures through autoregulation. However, this mechanism is overwhelmed when the systolic blood pressure is around 50mmHg at the brain level (correlating to 70mmHg at the cardiac level). This is what causes the light-headedness experienced in orthostatic hypotension.

There may be some predisposing factors:

• Hypovolaemia - haemorrhage, diarrhoea, infection/sepsis.
• Primary autonomic dysfunction - such as in Parkinson's disease or Lewy body dementia.
• Peripheral neuropathy may also cause autonomic neuropathy/failure - as seen in diabetes mellitus and amyloidosis.
• Medications:
• Alpha blockers - used for treating conditions such as benign prostatic hypertrophy.
• Central sympatholytics - tizanidine (a muscle relaxant).
• Diuretics
• Tricyclic antidepressants
• Antihypertensives - B blockers, CCB's, ACEi's, ARB's.
• Alcohol
• Ageing - decreases baroreceptor sensitivity
• Adrenal insufficiency

😷 Presentation

Postural hypotension can be asymptomatic, and in these cases it is not clinically significant. It becomes clinically significant when it becomes symptomatic. Symptoms can occur immediately or several minutes after standing up:

• Dizziness
• Presyncope
• Syncope
• Falls
• It occurs more frequently after meals, after exercise, in warm environments.
• Sometimes precipitated by coughing or defecating.
• If the cause is neurogenic, we also see a decrease in heart rate (by about 15 bpm).

🔍 Investigations

• Sitting BP followed by standing BP within 3 minutes - diagnosis confirmed if SBP is ≥20 mmHg lower (30 mmHg in hypertensives) or DBP is ≥10 mmHg lower.

🧰 Management