Non-invasive measurement of bladder pressure using an external catheter

Previous studies showed that, on the basis of a combination of maximum flow rate and isovolumetric bladder pressure, objectively diagnosing infravesical obstruction is possible. In this study, we validated a newly developed external catheter to measure non-invasively this pressure, which avoids the risk of damaging or infecting the urethral and bladder wall as occurs with invasive urodynamics. To evaluate the external catheter, we simultaneously recorded the internal bladder pressure signal (measured invasively) and the external pressure signal (measured non-invasively) in 40 non-obstructed and obstructed patients. Additionally, we tested whether the external pressure depended on bladder volume in five healthy volunteers. The simultaneously measured internal bladder pressure and external pressure showed good agreement in the non-obstructed patients. There was less agreement in the obstructed group. Nevertheless, the external pressure in these patients was significantly higher than in the non-obstructed patients. The maximum external pressure depended significantly on the bladder volume in all volunteers. We concluded that isovolumetric bladder pressure can be measured non-invasively with the external catheter. In non-obstructed patients, this pressure accurately represents the internal bladder pressure. We think that it is possible to distinguish between obstructed patients and patients with a weak detrusor by combining the non-invasively measured isovolumetric bladder pressure with a separately measured maximum flow rate. Neurourol. Urodynam. 18:455-475, 1999.