The normal bladder is characterised by a small rise in detrusor pressure - less than 10-15 cm of water - without undue sensation of urgency up to a capacity of 400-500 ml. Voiding is performed with a good flow rate, at a detrusor pressure less than 60-70 ml of water (lower in women), and empties the bladder completely.
In sensory urgency, early first sensation and a strong need to void prevents the bladder filling to a normal capacity.
Motor urgency due to detrusor instability is characterised by uninhibited contractions during filling which the patient cannot inhibit. There may be leakage.
Bladder outflow obstruction results in a low flow rate combined with a high voiding pressure. Imaging will provide additional information to elucidate the cause.
In 'genuine' stress incontinence, increasing intra-abdominal pressure, for example by coughing, causes involuntary loss of urine but detrusor pressure remains normal.
A hypotonic bladder fails to empty adequately as inadequate detrusor pressure is generated. Flow rate is usually low.
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