Purpose: To understand better the contractility and compliance characteristics of the detrusor in patients with varying degrees of outlet obstruction, we analyzed urodynamic studies in elderly men with obstructive and nonobstructive voiding dysfunction.
Materials and methods: All patients were evaluated with video urodynamics, including cystometry, isometric tests, voiding profilometry and post-void residual measurement. Bladder compliance, detrusor contractility, detrusor reserve, detrusor instability and the severity of outlet obstruction were determined in each patient. Patients were stratified into 4 groups: urodynamically normal, detrusor instability, outlet obstruction and outlet obstruction with detrusor instability.
Results: A significant correlation was found between the maximum isometric contraction pressure and the severity of obstruction in 168 patients. Maximum isometric contraction pressure was significantly greater in patients with than without obstruction, independent of detrusor instability. Although compliance was not significantly different among the groups, the proportion of patients with poor compliance (less than 30 ml./cm. water) was lowest in the normal group. The detrusor reserve was significantly less in patients with chronic retention (post-void residual more than 200 ml.) than in those with lower post-void residuals.
Conclusions: The increase in detrusor contractility with increasing outlet obstruction suggests a compensatory response to obstruction. Furthermore, a decrease in bladder compliance does not appear to be a consistent finding in patients with outlet obstruction, although the proportion of patients with poor compliance is higher in the group with obstruction and/or detrusor instability than in those with normal urodynamic findings. The decrease in detrusor reserve in patients with high post-void residual volumes suggests that the detrusor reserve reflects the degree of detrusor decompensation.