Post-micturitional Hypotension in Patients with Multiple System Atrophy

Background: Patients with multiple system atrophy (MSA) occasionally have episodes of syncope or pre-syncope after micturition.

Objective: To clarify the mechanism of these episodes by investigating the haemodynamic changes associated with micturition.

Methods: 25 patients with probable MSA and 16 age matched normal controls were studied. Continuous records of blood pressure and heart rate were made during water cystometry, along with the Valsalva manoeuvre, head up tilt testing, measurement of plasma noradrenaline, and calculation of coefficient of variance of RR intervals.

Results: Compared with normal controls, MSA patients had a lower baseline blood pressure, smaller blood pressure and heart rate increases during bladder filling, and an abnormal fall in blood pressure for a longer duration after voiding, resulting in significantly lower blood pressure than at baseline (mean systolic blood pressure reduction -15.2 mm Hg), and hypotension compared with control blood pressure (-29.0 mm Hg). The blood pressure fall was greater in patients with micturition syncope/pre-syncope than in those without. It was also greater in patients with abdominal straining resulting from difficulty in voiding. Other cardiovascular indices did not correlate with the fall in blood pressure.

Conclusions: Hypotension after voiding in MSA patients may result from generalised autonomic dysfunction and abnormal abdominal straining, resulting in micturition syncope.