Pressure-flow studies: an evaluation of within-testing reproducibility--validity of the measured parameters

The within-examination variation in selected test parameters in repeated pressure-flow studies was determined in a retrospective study of consecutive pressure-flow examinations in 105 patients. It was further evaluated to see whether there was a systematic change in the measured parameters during retesting. To see if variation and reproducibility were influenced by the procedure of investigation, i.e., transurethral or suprapubic, patients were grouped according to the method employed. Finally, the effect of detrusor instability on the measurements was evaluated. Using the Abrams-Griffiths nomogram, patients were classified as obstructed, equivocal, or unobstructed. The test-retest variations in classification were evaluated. We found a systematic variation in Pdet.Qmax' Pdet.Open' and Qmax during testing, indicating a physiological effect of repeated pressure-flow studies resulting in a less obstructed second voiding. Accordingly, 69% of the patients who shifted group of classification during retesting shifted to a group of lesser obstruction at the second voiding. Still, 88% of patients remained in the same group of classification of bladder outlet obstruction. Within- and between-patient variations and reproducibility of the test results were not influenced by the procedure of investigation, i.e., the transurethral or suprapubic method. However, we found variations suggesting a decrease in urethral resistance and bladder contractility from test to test in the transurethral group, whereas variations suggesting an isolated decrease in bladder contractility were seen in the suprapubic group. Detrusor instability per se does not seem to cause any systematic changes during repeated testing.