A flow rate cut-off value as a criterion for the accurate non-invasive measurement of bladder pressure using a condom-type catheter.

We developed a condom-type catheter to non-invasively measure the bladder pressure during interruption of the flow rate. The aim of the present study was to establish a minimum flow rate value at which a reliable bladder pressure measurement can be made with this catheter. We reanalysed data from 43 patients who completed a pressure-flow study and a non-invasive test. The patients voided without straining. During the test, we simultaneously measured the bladder pressure (invasively) and the condom pressure (non-invasively). The pressure increase in the condom after interruption of the flow rate was analysed in 40 of the 43 patients. A plot of the difference between the bladder pressure and the maximum condom pressure as a function of the flow rate revealed that in 70% of the patients who voided with a maximum flow rate exceeding 5.4 ml/s, the condom pressure accurately reflected the bladder pressure (+/-14 cmH2O). We conclude that to accurately and non-invasively measure the bladder pressure with a condom-type catheter, the maximum flow rate should exceed 5.4 ml/s.