THE VARIABLE OUTFLOW RESISTANCE CATHETER:: A NEW METHOD TO MEASURE BLADDER PRESSURE NONINVASIVELY

Abstract

PURPOSE: In a previous study an external condom catheter was used to measure noninvasively bladder pressure during interruption of the flow rate. The pressure increase in the condom sometimes caused a sphincter contraction that made bladder pressure measurement unreliable. Therefore, we developed a new variable outflow resistance catheter to measure noninvasively bladder pressure without interrupting the flow rate. MATERIALS AND METHODS: The new catheter consists of an incontinence condom connected to a set of various outflow tubes and a pressure transducer. A remotely controlled pneumatic valve was fitted over each tube to interrupt flow through it. We measured isovolumetric pressure, maximum flow rate, and pressure and flow rates at various outflow resistances in 9 healthy male volunteers. RESULTS: We derived a mathematical equation to estimate isovolumetric pressure from the pressure and flow rate values measured at various outflow resistances. The difference in the estimated and truly measured mean isovolumetric pressures plus or minus standard deviation was 0 +/- 6 cm. water. CONCLUSIONS: The new variable outflow resistance catheter may be used to measure isovolumetric bladder pressure noninvasively without interrupting the flow rate. It has been previously shown that a combination of this pressure and a separately measured maximum flow rate may be used to diagnose bladder outlet obstruction noninvasively.