To investigate phasic changes during filling cystometry that most accurately represent detrusor properties, regardless of other factors affecting detrusor contractility.

Seventy-eight patients (59 males, 19 females; mean age, 48.2 years) with spinal cord injuries were enrolled. Urodynamic studies were performed using a normal saline filling rate of 24 mL/min. We calculated bladder compliance values of the detrusor muscle in each of three filling phase intervals, which divided the filling cystometrogram into three phases referable to the cystometric capacity or maximum cystometric capacity. The three phases were sequentially delineated by reference to the pressure-volume curve reflecting bladder filling.

Bladder compliance during the first and second phases of filling cystometry was significantly correlated with overall bladder compliance in overactive detrusors. The highest coefficient of determination (r²=0.329) was obtained during the first phase of the pressure-volume curve. Bladder compliance during all three phases was significantly correlated with overall bladder compliance of filling cystometry in underactive detrusors. However, the coefficient of determination was greatest (r²=0.529) during the first phase of filling cystometry.

Phasic bladder compliance during the early filling phase (first filling phase) was the most representative assessment of overall bladder compliance during filling cystometry. Careful determination of early phase filling is important when seeking to acquire reliable urodynamic data on neurogenic bladders.