Ambulatory Urodynamics

This technique has only relatively recently become available. It relies on small catheter tip transducers and a portable recording system. As well as pressure any leakage is measured to within a few ml by a recording pad. The department at SGH is the only one in Scotland currently performing these tests. The clinical indication for the use of the technique would be cases where the symptoms of urgency and frequency point to an unstable bladder but static urodynamics failed to show it. Since ambulatory urodynamics also shows up leakage it is ideal for testing for genuine stress incontinence (GSI).

GSI is the involuntary leakage of urine in the absence of unstable bladder. It can sometimes be mimicked by an unstable bladder which is triggered by a cough. Thus the symptom is coincident with a stress event and is misdiagnosed as stress incontinence. Prior to the routine use of urodynamics many surgical procedures were carried out to correct what was thought to be stress incontinence. However many failed because the problem was really instability. GSI can be tested for using a static urodynamics system but there is limit to how much stress the patient can be made to do. With an ambulatory system realistic everyday stresses can be recreated.

The figure below shows a normal ambulatory trace lasting 30 minutes. The traces show (from the top) abdominal (rectal) pressure Pabd, intravesical pressure (Pves) detrusor pressure (Pdet) and leakage (Vol). The high compliance of the slow fill detrusor is seen. There is no instability and no leakage.

The diagram shows a one hour trace with several episodes of leakage. At this time scale it is not possible to analyse the cause of the leakage.

One hour trace with several episodes of leakage

The trace below shows an expanded part of the same trace.

Detrusor Instability with leakage time scale expanded

In the expanded trace it is clear that the leakage is cause by detrusor instability

This trace shows genuine stress incontinence. The noisy traces are caused by the patient jumping up and down. Most but not all of the motion artefacts are cancelled in the detrusor pressure. However there is no sign of the longer lasting phasic contraction associated with instability

Genuine Stress Incontinence

The following pie chart demonstrates the success of ambulatory urodynamics at detecting detrusor instability(n = 52)

52 patients had both conventional and ambulatory studies. 40% only showed instability on Ambulatory.

The following piechart demonstrates the success of ambulatory urodynamics at detecting stress incontinence.. (n = 52)

52 patients had both conventional and ambulatory studies. 17 % only showed GSI on ambulatory. There was a group of 8% who only showed leakage on conventional urodynamics. It is not immediately obvious why this group should occur because ambulatory allows a wider range of exercises. However ambulatory patients are sent off to perform the exercises themselves and it possible some are not pushing themselves as far as the staff would push them at conventional studies.

Another area where ambulatory studies have proved useful is in the diagnosis of giggle incontinence. Giggle Incontinence is most common in the young and has been very difficult to demonstrate because of the infrequency with which it occurs and the difficulty in making a patient laugh while undergoing urodynamics.

Ambulatory Urodynamics takes the patient out of the clinic and into TV rooms etc... where in time and with highly amusing staff or relatives it can be demonstrated as below.

Cystometry for young boy with symptoms of giggle incontinence
Ambulatory urodynamics for young boy with symptoms of giggle incontinence

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