The Measurement and Interpretation of Urethral Pressures Obtained by the Method of Brown and Wickham

Abstract

Summary— The most significant error in routine measurement of urethral pressure by the Brown‐Wickham method is caused by the slow response of the system to increasing pressure. Errors due to viscous pressure losses in the measuring catheter and to variable orientation of the catheter sideholes are not normally important.The distensibility of the urethra may be estimated from the variation of the measured pressure with infusion flow rate in the range above 2 ml/min.In highly distensible urethras the pressure actually measured is similar to the true pressure in the undistended urethra, but in less distensible urethras this is not so.Substantial leakage, at a flow rate of 2 ml/min or more, begins to occur when the intravesical pressure is approximately equal to the maximum pressure in the undistended urethra. Therefore, in highly distensible urethras the maximum measured pressure is a satisfactory guide to the intravesical pressure needed for substantial leakage. In less distensible urethras, however, substantial leakage may occur when the intravesical pressure is perhaps 25 cm H2O below the maximum pressure measured in the urethra.Leakage at very low flow rates may be possible through some urethras when the intravesical pressure is very low indeed. The urethral closure pressure profile, as ordinarily measured, is not a reliable guide to the possibility of such leakage.With care, the method of Brown and Wickham gives satisfactory measurements of the urethral closure pressure profile. However, the maximum profile pressure exceeds, sometimes by a considerable amount, the bladder pressure needed to cause leakage.