Abstract
The aim of this study is to investigate how male urinary flow is altered when measured from a supine posture relative to seated voiding. The theoretical impact of any changes on urodynamic diagnosis will also be considered. Water was poured from a calibrated device into a flow meter from geometry simulating seated male voiding, then supine male voiding through two different voiding aids; each condition was repeated nine times. Peak flow rate and its latency were marked carefully, and compared within and between conditions.
The primary outcome measures were changes in peak flow rate and its latency for supine voiding. Subsequent changes to diagnostic classification on the Schafer nomogram provided a secondary outcome measure- achieved by plotting the original and corrected pressure-flow coordinates of real patients and observing any category changes. Hydrostatic pressure was then estimated to assess factors unrelated to the patient or the apparatus that could influence the primary outcome measures. Finally, calculation of Reynolds numbers allowed the likelihood of turbulence to be judged, and the resultant effect this could have on flow recordings.
Recumbent flow was significantly slower than seated flow, and both its onset and its peak were delayed. However, the attenuation and lag observed by employing a modified Cystoaid were much smaller than when using a rectangular tube. Adjusting clinical data for these changes resulted in a reduction in the Schaefer Nomogram classification of detrusor strength for both aids. The changes lead to obstruction being underestimated or overlooked. A clinically significant re-categorisation (resulting in a change of management) is predicted when using the rectangular tube.
A component of the errors in both aided conditions is explained by a reduction in hydrostatic pressure as the source was tilted. Additionally, turbulence could be introduced by the Cystoaid during the fastest flows. The use of voiding aids could therefore convolute identification of clinical features and artefacts during qualitative analysis.
