It is our practice to fill the bladder initially in the supine position and the volume at first sensation of filling is noted. When the subject first experiences discomfort, the radiographic table is tipped toward the standing position and subsequent bladder filling discontinued when at the maximum tolerated capacity.During bladder filling the patient is asked to consciously suppress bladder contraction and may be asked to cough or heel bounce. The patient is then turned to the oblique position relative to the X-ray machine and asked to void into the flowmeter provided.

In units where a tipping table is not available, the study can be carried out in the sitting or standing position initially; but it is important to subsequently stand the patient upright at the end of the study to assess where there is postural detrusor instability and to determine whether there is stress incontinence; in the absence of radiological screening this is assessed with the patient standing with legs slightly apart and squatting.

Throughout the study continuous rectal pressure, total bladder pressure and electronically subtracted detrusor pressure (total bladder pressure minus rectal pressure) measurements are sampled at a predetermined rate (usually 1 Hz) and the results displayed on the video display unit / stored to disc / polygraph chart recorder; depending on the equipment in use. Figure 20.4a and b shows a typical workstation and schematic.

Videodynamics provides an excellent method of evaluating the urethral outlet in female patients with urinary incontinence, males with complex voiding problems and are essential to the optimum management of neurological patients. Standing quietly and partially obliqued,the bladder neck position may be abnormally low, below the level of the upper third of the symphysis pubis, signifying loss of pelvic floor support in female patients with hypermobile urethras/ anatomical stress incontinence. Coughing or valsalva maneuvers cause these vesicourethral units to descend and leak. With termination of the increased intra-abdominal pressure the bladder neck quickly “springs back” to its original position terminating leakage. The semi-lateral/ oblique position enables to distinguish between the bladder neck from a dependent cystocele and it also helps to evaluate the size and functional significance of the cystocele.

Breaking or funneling of the bladder neck probably represents a normal finding,is common

in continent females, but should be distinguished from a rectangular-shaped incompetent bladder neck common in patients with intrinsic sphincter deficiency (ISD). Typically patients with pure ISD as the cause of their incontinence demonstrate severe leakage with minimal intra-abdom- inalpressureincreasesandminimalurethrovesical hypermobility. The urethra does not spring back but appears to hold open and continue leaking even after the stress event. Patients often have both bladder neck hypermobility and ISD and experience is necessary in order to interpret their relative functional significance.

Cystourethrography via the adjacent X-ray screening apparatus allows the synchronous display of pressure and flow, and also radiographic data relating to bladder morphology e.g. diverticula, vesicoureteric reflux and the appearances of the bladder outlet and urethra, to be displayed alongside the numerical data on a video display unit.

Cystometric Findings

As filling continues the patient is asked to confirm the following bladder sensations which are recorded on the computer:

•First desire to void

•Strong desire to void

•Desire at which the patient cannot delay micturition (Maximum cystometric capacity)

•Urgency – sudden compelling desire to void

•Bladder pain – should not occur during filling

The computer calculates the pressures and plots them on a temporal graph. The above sensations are recorded at specific times and give an indication of how full the bladder was when these sensations occurred. Figure 20.5 shows a typical readout from the study, showing both storage and voiding phases with regular quality controls (coughing). The detrusor pressure is the result of the intravesical pressure minus the intra-abdominal pressure.

The four graphs in the order produced are:

•Intra-abdominal pressure (Pabd)

•Intra-vesical pressure (Pves)

•Detrusor pressure (Pdet)

•Urinary flow rate (Q)

Practical Points: Since a number of variations in technique are currently available, the following points deserve specific consideration.

i.Type of catheter

a.Fluid-filled catheter – specify number of catheters, single or multiple lumens, type of catheter, size of catheter.

b.Catheter tip transducer – specifications vary between manufacturers; these catheters

tend to be expensive and rather too fragile for routine use.

ii.Measuring equipment.

A number of commercial urodynamic systems are currently available. These vary greatly in terms of sampling rate, associated computer software backup,and price.A major problem with existing computer programs is the ease with which such programs will

Figure 20.5. a typical graphical display of the pressure flow data, showing both storage and voiding phases with regular coughing acting as a quality control (small blips in Pdet).the graph shows good contraction of the detrusor during the voiding phase and no contractions during the storage phase. not included are the sensations as described by the patient, which will be plotted along the x-axis at the time they occurred, allowing us to calculate volumes at which sensory perceptions occur.22

Pabd

(cm H2O)

Pves

(cm H2O)

record artifacts which can then bias the results of the subsequent automatic data analysis. The investigator is strongly advised not to rely upon the computer generated data sheets but to use an appropriate standardized reading sheet which allows interpretation of the urodynamic findings by the investigator.

iii.Test medium (liquid or gas)

This is obviously not applicable to catheter tip transducers. The advantage of equipment using gas as a medium is that it can be more compact and is therefore more easily portable. A major drawback with gas cystometry is its susceptibility to artifact being introduced by changes in the temperature of the gaseous medium; a far less important consideration when fluid is used.

iv.Position of patient (e.g. supine, sitting, or standing).

v.Type of filling

This may be by diuresis or catheter. Filling by catheter may be continuous or incremental; the precise filling rate should be stated (vide infra).When the incremental method is used the volume increment should be stated.

vi.Continuous or intermittent pressure measurement

Continuous pressure measurement is of greatest usefulness in clinical practice; in patients for example with a suprapubic catheter and no urethral access, staged measurement of pressures can be carried out through the suprapubic catheter.