Functional assessment of the bladder

The urinary bladder has two functions: to store and to empty. A frequency-volume chart completed by the patient provides useful information about voiding intervals, possible factors provocative for incontinence, functional bladder capacity and daily urine volume. Filling cystometry is used primarily to evaluate reflex function in the storage phase, giving information about the presence or absence of detrusor instability and (in combination with urethral EMG) about detrusor-sphincter coordination. Information is also obtained about bladder sensation, bladder capacity and bladder compliance. Detrusor function during emptying is closely related to outflow conditions and therefore demands simultaneous registration of detrusor pressure and urinary flow rate. An inverse relation exists between detrusor pressure and flow rate, which means that reduced flow rate causes increased detrusor pressure for the same detrusor power. Underactive detrusor function will result in low detrusor pressure and low flow rate. The finding of a non-contractile detrusor may indicate psychogenic inhibition or a neurogenic lesion. Sacral evoked potentials and denervation supersensitivity tests may help to distinguish between these conditions.