Comparison of air-charged and water-filled urodynamic pressure measurement catheters.

AIMS: Catheter systems are utilized to measure pressure for diagnosis of voiding dysfunction. In a clinical setting, patient movement and urodynamic pumps introduce hydrostatic and motion artifacts into measurements. Therefore, complete characterization of a catheter system includes its response to artifacts as well its frequency response. The objective of this study was to compare the response of two disposable clinical catheter systems: water-filled and air-charged, to controlled pressure signals to assess their similarities and differences in pressure transduction. METHODS: We characterized frequency response using a transient step test, which exposed the catheters to a sudden change in pressure; and a sinusoidal frequency sweep test, which exposed the catheters to a sinusoidal pressure wave from 1 to 30 Hz. The response of the catheters to motion artifacts was tested using a vortex and the response to hydrostatic pressure changes was tested by moving the catheter tips to calibrated heights. RESULTS: Water-filled catheters acted as an underdamped system, resonating at 10.13 ± 1.03 Hz and attenuating signals at frequencies higher than 19 Hz. They demonstrated significant motion and hydrostatic artifacts. Air-charged catheters acted as an overdamped system and attenuated signals at frequencies higher than 3.02 ± 0.13 Hz. They demonstrated significantly less motion and hydrostatic artifacts than water-filled catheters. The transient step and frequency sweep tests gave comparable results. CONCLUSIONS: Air-charged and water-filled catheters respond to pressure changes in dramatically different ways. Knowledge of the characteristics of the pressure-measuring system is essential to finding the best match for a specific application.

Direct bladder stimulation with percutaneous electrodes and impedance monitoring of volume in an SCI animal model.

Bladder responses to percutaneous electrodes were investigated with stimulation in three male spinal cats. The animals had been spinalized (T1 level lesion) 10 weeks prior to these studies and had been instrumented with chronic bladder had been spinalized (T1 level lesion) 10 weeks prior to these studies and had been instrumented with chronic bladder wall electrodes and suprapubic bladder catheters for filling and pressure recording. percutaneous stimulation in tethered animals was conducted wit hook electrodes inserted with a needle in the abdomen bilaterally adjacent to the bladder trigone. Stimulation was conducted with 40 Hz pulse trains of 10 to 30 mA for three seconds. Stimulation with both percutaneous and chronic electrodes induced high bladder pressures and voiding. In addition, with chronically implanted electrodes, impedance monitoring of bladder volume was found to be an effective recording technique.

Urodynamic measure of urethral cross-sectional area: application for obstructive uropathy.

A conductance formula was developed based on pressure (P) and flow (Q) data collected from rigid tubes with a cross-sectional area in the range of the flow controlling zone of the urethra. Curve fitting of data resulted in an exponential formula and a simple proportionality constant related tube of differing cross-sectional area. The resulting formula estimates cross-sectional area based on P and Q data and is in the form of a conductance ratio because Q is in the numerator and P is in the denominator. The formula is AEFm = 3.5 Q/P0.58, where AEFm is the area equivalent factor-male and Q is measured in ml/sec and P is cm H2O. To further introduce the estimate of cross-sectional area, urodynamics were retrospectively reviewed from 19 males over the age of 50 with complaints of prostatism. The AEFm was plotted on standard urodynamic records much like P and Q data. The onset of voiding was characterized by a rapid increase in urethral area. Maximal cross-sectional area obtained at maximal flow was 2.9 +/- 1.4 mm2. The maximal urethral area per unit of applied detrusor pressure, an estimate of urethral compliance, was 0.06 +/- 0.6 mm2/cm H2O. This latter measure may help to compare patients with widely different detrusor pressures. The urodynamic data from two young adult males is also presented for comparison. Their average maximal urethral cross-sectional area was 7.1 mm2. Their average area per unit of applied detrusor pressure was 0.15 mm2/cm H2O. These larger values contrast sharply with the BPH group. The AEFm clearly shows urethral function in terms of the principal factor regulating the urine flow rate, the urethral cross-sectional area.

Measurement of total urethral compliance in females with stress incontinence.

Urodynamic evaluation of stress incontinence has failed to result in consistent diagnostic parameters. Using retrospective female bladder pressure and urine flow data, we evaluated two parameters based on a conductance formula. This formula was derived from fitting a classical fluid dynamic equation to published data of voiding cystourethography. The Area Equivalent Factor-female at maximal flow represents maximal urethral opening and this value further divided by the pressure is the total urethral compliance. A stress incontinent group had a strong trend toward greater maximal urethral opening and total urethral compliance than a continent group. These parameters may, therefore, have potential in the evaluation and understanding of stress urinary incontinence.

Bladder inhibition by penile nerve stimulation in spinal cord injury patients.

Detrusor hyperreflexia causing voiding dysfunction in spinal cord injury patients is a difficult problem and is not always treated effectively by anticholinergic agents. We have been investigating electrical stimulation methods to inhibit hyperreflexia and dorsal penile nerve stimulation is the most promising. Six chronic suprasacral spinal cord injury men (average age 36 years) underwent stimulation testing with water cystometry before, during and after stimulation. Dorsal penile stimulation was done with carbon rubber butterfly electrodes (Medtronic) with parameters of 5 pulses per second, 0.35 msec. pulse duration, and current at a level above the threshold for pelvic twitching activity and adjusted for optimal bladder effect (range 25 to 70 mamp.). In all 6 patients the cystometrogram during stimulation showed an increase in bladder volume over the prestimulation cystometrogram (range 27 to 150%). In 2 patients there was no detrusor activity after filling to 500 cc. Stimulation was then stopped and a spontaneous contraction occurred. The cystometrogram conducted after the stimulus also had less volume than that performed during stimulation but it was larger than the prestimulation volume. Penile nerve stimulation was painless with no side effects. Penile nerve electrical stimulation is effective for inhibiting bladder hyperreflexia and should be easily adaptable for chronic home use as an alternative to current therapy.