Urodynamic assessment of bladder function.

Bladder function in micturition may be studied, without interference from the urethra, through 2 parameters, Piso and Q, which are measures respectively of the maximum pressure and of the maximum flow rate that the bladder can generate, i.e. of its intrinsic strength and speed. These parameters may be determined in a standard urodynamic investigation if the patient interrupts voiding for a short time with the external sphincter. The normal ranges of Piso and Q depend only slightly on age and sex and seem to be as follows: Piso, 50 to 100(+)cm H2O in both sexes; Q, 35 to 120 ml s-1 in males, 20 to 80 ml s-1 in females. There are significant differences in both parameters between different groups of patients. Many females, with stress or urge incontinence or with urgency, have bladders which seem to be weaker than normal (low Piso). The majority of proximally obstructed males, and many who have been surgically relieved of obstruction, have bladders which are significantly slower than normal but are of normal strength (low Q, normal Piso). Therefore the characteristic response of the detrusor to obstruction appears to be not the expected mechanical hypertrophy (Turner Warwick et al., 1973) but reduction in intrinsic speed. In contrast, a few proximally obstructed males and most males with a history of primary enuresis (persisting after 6 years of age) have bladders of normal speed and of strength significantly greater than normal (normal Q, high Piso), suggesting true mechanical hypertrophy of the detrusor. Females with a history of primary enuresis do not show this pattern so clearly. Since these sex- and disease-related differences must surely be of clinical significance, and since it is so easy to measure Piso and Q by the method given in section (e) of the Appendix, those who are concerned with clinical urodynamics are urged to investigate bladder function in this or some equivalent way (e.g. that proposed by Schäfer and Melchior (1975)).