BOO (bladder outlet obstruction) is usually treated only after the patient presents with LUTS (lower urinary tract symptoms). However, by the time bothersome symptoms emerge bladder dysfunction may have progressed to the point where it may no longer be reversible. Using traditional invasive urodynamics to evaluate voiding function and bladder pressure is inconvenient for patient and practitioner, uncomfortable and frequently non-physiologic. We developed a device, which creates a closed system during voiding and thus measures bladder pressure without use of a catheter.

A group of 33 male patients with known symptoms of BPH in a community practice were enrolled in this study. They were instructed to void into a device (NUC – Noninvasive Urtroflow-Cystometer), which is a closed airspace and can measure the pressure generated by the urine flow. This is possible by making a tight seal between the glans and the device by an intervening attachment called UED (urethral extender device). This creates a closed space between the meatus and the UED, by a mild negative suction pressure at the point of contact, with pressures between 150-300 mm Hg. The suction is created from a circular slit, which surrounds the opening into the measuring chamber.

The measuring chamber is able to analyze the backpressure created during voiding and generates pressure-time curves. This pressure is reflective of bladder pressure as the bladder pressure is exposed through an open urethra during voiding. When the back pressure reaches a preset level (i.e. – 30 mm Hg) a solenoid valve opens and releases the air displaced by the urine within the UED so the pressure returns to 0 mm Hg. This prevents an increase in backpressure in the bladder to the point of being noticeable or uncomfortable. The valve then closes and the process is repeated until the voiding is completed. Analysis of the pressure-time curves and the flow-pressure curves derived from the pressure-time curves, provides measure of urine flow rate (uroflowmetry), urethral resistance (“obstruction” to flow), bladder pressure (detrusor strength). The slope of the flow-pressure curves helps determine the relative contribution of urethral obstruction versus bladder weakness to diminished urine flow. When the flow-pressure curve is extrapolated to the X and Y-axes the maximum urine flow is noted at zero backpressure and the maximum bladder pressure extrapolates at zero flow (isovolumetric bladder pressure).

Each subject voided in the device at the sensation of full bladder (normals: n=2; patients: n=33). The graph below summarizes the data.

The data from our study identified easily 4 broad categories: normal subjects (normal flows, normal bladder pressures), compensated bladders (normal flows, high bladder pressures) decompensated bladders with reduced flows and lower pressures, and hypotonic bladders with reduced flows and reduced pressures. T-tests showed p values less than 0.001 for differences between the normal and the symptomatic subjects in all variables (flow, pressure and total volume).

The noninvasive uroflow-cystometer easily differentiated between normal and abnormal lower urinary tract function in men with bladder outlet obstruction and between distinct patient subpopulations. This device has the potential to significantly impact the standard of care for patients being evaluated for BPH with LUTS. The NUC identified obstructed subjects with normal flow that was the result of bladder pressure compensation, as well as obstructed subjects. This can lead to early medical intervention in the treatment of bladder changes related to bladder outlet obstruction.