A technique for measurement of related values of pressure and cross-sectional area in the male urethra

A probe for measurement of related values of cross-sectional area and pressure in the male urethra was constructed. The probe allows induction of variable pressures or fluid volumes in a distensible balloon located in the urethra and simultaneous recording of related values of cross-sectional area and pressure. Cross-sectional area is measured in the range of 11–102 mm2 using the field-gradient principle. Pressure is measured in the range of 0–250 cmH2O using tip transducers. The time constant for cross-sectional area measurement is 0.02 s and that for pressure measurement, 0.007 s. The pressures required to reach the maximal and minimal cross-sectional areas of the balloon are 2.8 and-2.4 cmH2O, respectively. The shape of the probe after its placement in the urethra was studied by transrectal ultrasound in five volunteers. The results showed that the measurement error caused by the slope of the balloon walls or the forced bending of the catheter did not exceed 5%. The method enables a description of the biomechanical properties of the male urethra at rest in terms of estimated pressure at zero cross-sectional area, elastance, and stress-relaxation and at voluntary contraction in terms of work and power as evaluated at well-defined anatomical locations.