It is now widespread practice to use an invasive pressure-flow study (PFS) to assess patients with suspected bladder outflow obstruction (BOO). Concern with this technique centres around its invasive and unpleasant nature for patients. We are developing a non-invasive method of measuring bladder pressure by means of an inflatable cuff placed around the penis that removes the need for catheterisation and rectal lines.
The test involves inflation of the cuff to interrupt urinary flow during voiding to allow measurement of isovolumetric intra-vesicular pressure (Pves,iso). After flow is interrupted the cuff is deflated and voiding allowed to continue. We feel it is important that flow should recover, to indicate that detrusor contraction was maintained for the duration of the measurement. Typically 3 or 4 inflation cycles can be performed during a single micturition. In this study we have investigated the following questions:
1) How does the voiding pressure after interruption and resumption of flow compare with voiding pressure before the interruption of flow commenced?
2) Does interruption of the urinary stream cause a rise in bladder pressure as predicted by current theory of detrusor physiology?
After the interruption of the urinary stream was removed and free flow resumed Pdet and Pves return to their pre-interruption values. The fact that this occurs for both Pdet and Pves implies that abdominal pressure remains a constant factor during the test. Current models of bladder physiology suggest that detrusor power is a function of Pdet and flow, and that as one decreases the other increases if power remains constant. An isovolumetric increase in bladder pressure should therefore occur if flow is prevented and this was generally the case in our data although the magnitude of the effect was not as large or consistent as might would been predicted.
McIntosh SL, Drinnan MJ, Pickard RS, Robson WA, Ramsden PD, Griffiths CJ. Non-invasive bladder pressure monitoring - how does interrupting the urinary stream affect intra-vesicle pressure? Neurourol Urodynam 2001;20:382-3.
Clive J. Griffiths or Dr. Michael J. Drinnan, Freeman Unit, Newcastle upon Tyne. Tel: +44 (0)191-223-6161.
Regional Medical Physics Department, Freeman Hospital, Newcastle upon Tyne, NE7 7DN, UK.
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