Pressure/flow studies preoperatively and postoperatively in patients with benign prostatic hypertrophy: Estimation of the urethral pressure/flow relation and urethral elasticity

Abstract

AbstractPressure/flow studies were performed in 28 men with benign prostatic hypertrophy. Twenty‐three of the men were also studied postoperatively. Urethral function during micturition was quantified by the urethral pressure/flow relation, pdet = pmo + Lm Qm, where Pdet is detrusor pressure, Pmo is minimal opening pressure. Q is flow rate, and m and Lm are parameters. Using this method to quantify urethral function, three urodynamically different types of obstruction can be defined. In the first of these, Pmo is elevated corresponding to Schäfer's compressive obstruction. The second is a constrictive type of obstruction in which m ≥ 4/3 and Lm is elevated and the third is a low‐compliant type of obstruction in which m ≤ 1 and Lm is elevated. The two latter types of obstruction may be combined with a compressive obstruction.The preoperative pressure/flow relations were mostly characterized by a very high Pmo, a moderately elevated Lm, and a low m. Thus the majority of patients had a combination of compressive and low‐compliant obstruction. Postoperatively, micturitions were much improved and the pressure/flow relations often had an even lower Pmo than normal, a normal Lm, and a high m.From the pressure/flow relations, the elasticity of the flow‐controlling zone can be estimated and described by the urethral pressure/area relation, p(A) = pmo + Kn An, where p(A) is the intrinsic urethral pressure, A is the cross‐sectional area of the flow‐controlling zone and Kn and n are parameters describing the distensibility of the flow‐controlling zone. Preoperatively, the flow‐controlling zone had a low distensibility. The shape of the curve suggested that the urethra could have been distended further by higher pressure. Postoperatively, the urethra was distended to larger cross‐sectional areas, but in many cases the shape of the curve suggested that distension was restricted by fibrosis. Median and range values for the model parameters as well as discriminating limits between the preoperative micturitions and micturitions in elderly men without voiding problems are presented.The exponent m is not perfectly reproducible but tends to be the same if a person performs several micturitions. The residual sum of squares is often increased more than 100% if an exponent m value other than the optimal one is used for curve fitting.Results when the micturitions were analysed with Schäfer's model and classified using the maximum flow/pressure at maximum flow diagram recommended by the Interenational Continence Society are also shown.