Comparative study of air and water measurements of peak and stabilized static urethral pressures

Air and water were forced through female dogs' urethras to determine static urethral pressures. The cauda equina was sectioned to eliminate reflex responses to urethral manipulation, and the urethras were compressed circumferentially with inflatable Silastic cuffs. The peak and stabilized urethral pressures were recorded at flow rates between 20 and 150 ml./min. while cuff pressures were varied between 0 and 100 cm. of water. When the fluid recordings of static urethral pressure were compared with Millar transducer tip catheter measurements of urethral pressure, there were no statistically significant differences between the air cystometer, aneroid sphygmomanometer, and Millar catheter recordings of urethral pressure. At these high flow rates, the water recordings of urethral pressure were significantly higher than the Millar catheter determinations of static uretheral pressure.