Postural hypotension: the blood pressure reading almost nobody takes

Orthostatic hypotension is defined as a fall of at least 20 mmHg systolic or 10 mmHg diastolic within three minutes of standing. It affects roughly 5 to 30 per cent of community-dwelling older adults depending on the population studied, and considerably more in residential care and among those on multiple medications.

It causes dizziness, light-headedness, blurred vision, neck and shoulder discomfort — the coat-hanger distribution, from hypoperfusion of the postural muscles — weakness, and syncope. It is an established and important contributor to falls and fractures.

And it is routinely missed, for a simple reason: blood pressure is almost always measured with the patient sitting, and the diagnosis requires measuring it standing.

The physiology

Standing shifts roughly 500 to 1,000 ml of blood into the lower body. In a healthy system, baroreceptors detect the fall in central pressure within seconds and trigger vasoconstriction and an increase in heart rate.

Several parts of this fail with age. Baroreceptor sensitivity declines. Arterial stiffness reduces the vasoconstrictor response. Cardiac diastolic function worsens, so the heart fills less well with a reduced return. And renal sodium conservation is less efficient, so intravascular volume is more easily depleted.

The heart rate tells you something

A useful distinction that is easy to make at the bedside.

If blood pressure drops and the heart rate rises appropriately — by more than about 15 beats per minute — the autonomic reflex is intact and the problem is likely volume depletion, medication, or deconditioning.

If blood pressure drops and the heart rate barely changes, this suggests neurogenic orthostatic hypotension: a failure of the autonomic reflex itself. That points toward Parkinson's disease, multiple system atrophy, pure autonomic failure, diabetic autonomic neuropathy, or amyloidosis, and warrants further assessment.

The usual causes

Medication is the commonest and the most fixable. Diuretics, alpha blockers such as doxazosin and tamsulosin, nitrates, other antihypertensives, tricyclic antidepressants, some antipsychotics, and dopaminergic drugs for Parkinson's.

Volume depletion — dehydration, blood loss, poor intake.

Prolonged bed rest and deconditioning, which is why it is so common after a hospital stay.

Neurodegenerative disease, as above.

Adrenal insufficiency and other endocrine causes, uncommon but important.

Two variants worth knowing

Postprandial hypotension — a fall in blood pressure within two hours of eating, caused by splanchnic blood pooling during digestion. It is common in older adults, more pronounced after large or carbohydrate-heavy meals, and is a frequent cause of after-lunch falls. Smaller, more frequent meals help, as does avoiding alcohol with them and sitting for a while after eating.

Supine hypertension. A substantial proportion of people with neurogenic orthostatic hypotension have high blood pressure when lying down — the same failed autonomic regulation working in the other direction. This makes treatment genuinely difficult, because raising standing pressure worsens lying pressure. Head-of-bed elevation by 10 to 20 degrees at night helps both.

Management, in order

Review the drugs first. Reducing or removing a contributing medication resolves a meaningful proportion of cases and is the intervention with the best benefit-to-harm ratio.

Increase fluid and salt where not contraindicated. Rapidly drinking around 500 ml of cold water produces a measurable pressor response within minutes, lasting an hour or so — genuinely useful before standing for a period, and one of the more elegant non-pharmacological interventions available.

Compression. Abdominal binders are more effective than stockings, because the splanchnic bed holds more volume than the legs. Thigh-high stockings outperform knee-high ones.

Physical counter-manoeuvres — crossing the legs and tensing, squeezing a ball, clenching the buttocks — raise pressure and can abort an episode.

Rising in stages. Sit on the edge of the bed, pump the ankles, wait, then stand. Simple and effective.

Avoid the aggravators — hot baths, large meals, alcohol, straining, prolonged standing still, and getting up quickly at night.

Medication — fludrocortisone, midodrine or droxidopa — where the above is insufficient. All carry risks, particularly supine hypertension and, with fludrocortisone, fluid overload and hypokalaemia.

The thing to ask for

If you have had unexplained falls, dizziness on standing, or near-fainting, ask specifically for a lying and standing blood pressure. It takes four minutes, it is not part of a routine check, and it identifies a treatable cause of falls in a substantial number of people who have been told their unsteadiness is simply age.