International Continence Society Subcommittee on Standardisation of Terminology of Pressure-Flow Studies flow studies in many different sections. This report is a revision and expansion of Sections 4.2 and 4.3 and parts of Sections 6.2 and 7 of the 1988 report. It contains a recommendation for a provisional standard method for defining obstruction on the basis of pressure-flow data. 2. Evaluation of Micturition 2.1. Pressure-Flow Studies At present, the best method of analysing voiding function quantitatively is the pressure-flow study of micturition, with simultaneous recording of abdominal, intravesical and detrusor pressures and flow rate (Fig. A.1.6.1). Direct inspection of the raw pressure and flow data before, during and at the end of micturition is essential, because it allows artefacts and untrustworthy data to be recognised and eliminated. More detailed analyses of pressure-flow relationships, described below, are advisable to aid diagnosis and to quantify data for research studies. The flow pattern in a pressure-flow study should be representative of free flow studies in the same patient. It is important to eliminate artefacts and unrepresentative studies before applying more detailed analyses. Pressure-flow studies contain information about the behaviour of the urethra and the behaviour of the detrusor. Section 2.2 deals with the urethra. Detrusor function is considered in Section 2.3. 2.1.1. Pressure and Flow Rate Parameters Definitions See Fig. A.1.6.1 and Table II; see also Table II Appendix 1, Part 2. Maximum flow rate is the maximum measured value of the flow rate. Symbol Qmax Maximum pressure is the maximum value of the pressure measured during a pressure-flow study. Note that this may be attained at a moment when the flow rate is zero. Symbols: P abd, max, P ves, max, P det, max. Pressure at maximum flow is the pressure recorded at maximum measured flow rate. If the same maximum value is attained more than once or if it is sustained for a period of time, then the point of maximum flow is taken to be where the detrusor pressure has its lowest value for this flow rate; abdominal, intravesical and detrusor pressures at maximum flow are all read at this same point. Flow delay (see Section 2.1.2) may have a significant influence and should be considered. Symbols: P abd, Qmax, P ves, Qmax, P det, Qmax .
Detrusor wall thickness decreases continuously while the bladder fills to 50% of its capacity and then remains constant until 100%. Therefore, detrusor wall measurements were performed in patients when the bladder was filled to maximum capacity only. Mean detrusor wall thickness for unobstructed (n = 14), equivocal (n=23) and obstructed patients (n=33) were 1.33, 1.62 and 2.4 mm, respectively (P <0.001). With increasing CHESS letters and CHESS numbers, the thickness of the detrusor wall increased as well (P< 0.001). The positive predictive value of detrusor wall measurement (95.5% for a cut-off value greater than or equal to 2 mm) was superior to all other predictors investigated. The thickness of the detrusor wall increases depending on the extent of BOO. Both constrictive and compressive BOO lead to an increase in detrusor wall thickness. BOO is found in 95.5% of men with a detrusor wall thickness greater than or equal to 2 mm. Measuring the thickness of the detrusor wall can be used as a screening test to detect BOO.
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