The normal detrusor if filled slowly
accepts 300 - 600 ml without rise in pressure.
If the bladder undergoes phasic contraction while the patient is trying to inhibit voiding this is called overactivity.
This is a particluarly low pressure
example. Some might feel it was fanciful to diagnose on this. However note
how leakage occurs coincident with the small contractions. We also have
other examples from the same patient all coincidetn with leakage and
urgency. In the past definitions of Detrusor overactivity have included
a minimum pressure rise e.g. 15 cm water, but this is now known to be misleading.
If the patient above can be incontinent with pressure rises of a few cm
water, then any definition must include such contractions.
The current definition is
provocation during the filling phase while the patient is attempting to inhibit micturition."
For a textbook example of Detrusor overactivity click here. In practice there can be much higher amplitude contractions
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