Application of detrusor power curve analysis in urodynaimc studies

Objective To establish a calculation method for the voiding work parameters by using the detrusor power curve and to evaluate its clinic efficacy. Methods From January 2001 to January 2011, 132 male patients with benign prostate hyperplasia who underwent urodynamic tests were retrospectively reviewed. The patients' age ranged from 45 to 84 years old (mean 57 years old). All patients had no previous history of neurological disease and no positive findings in neurological examinations. The voiding work of bladder, the voiding power of bladder and voiding energy consumption were calculated by using the detrusor power curve method and the linearized passive urethral resistance relation analysis was conducted. According to the detrusor status, all patients were divided into the decreased detrusor pressure group, the normal detrusor pressure group and the increased detrusor pressure group. Meanwhile, normal urethral resistance group and the increased urethral resistance group were classified according to the urethral resistance status. The detrusor pressure at maximal flow rate (PdetQmax), the maximal flow rate (Qmax), the projected isovolumetric pressure (PIP), the voiding work, the voiding power and the voiding energy consumption were compared among the different groups. Results There were 56 cases, 58 cases, 18 cases in the decreased, normal and the increased detrusor pressure group respectively. The voiding work were (1.1±0.5)J, (1.7±0.7)J, (2.1±1.2)J; the voiding power were (15.3±7.3) mW, (31.9±12.6) mW, (42.5±21.1) mW; and the voiding energy consumption were (3.9±1.2)J/L, (5.2±1.9)J/L, (6.2±3.2)J/L in those three groups, respectively. With the increasing of detrusor pressure, PdetQmax, Qmax, PIP, the voiding work, the voiding power and the voiding energy consumption all increased among three groups with significant difference (P<0.05). There were 51 cases, 81 cases in the normal and the increased urethral resistance group. The voiding work were (1.5±0.7)J and (1.5±0.8)J; the voiding power were (32.3±13.2) mW and (22.6±16.3) mW and the voiding energy consumption were (3.8±0.7)J/L and (5.4±2.4)J/L in two groups. The increased urethral resistance group had higher PdetQmax and voiding energy consumption (P<0.05) and lower Qmax and voiding power (P<0.05) than those in the normal urethral resistance group. However, the differences of PIP (P=0.438) and the voiding work (P=0.546) between the two groups were not determined. Conclusions The detrusor power curve method can be used to calculate the work parameters of voiding. This method can be applied to evaluate the compensatory state of bladder and is conductive to urodynamic analysis in low detrusor pressure status. Both detrusor pressure and urethral resistance had significant impact on the work capacity of bladder. Key words: Urodynamics; Bladder function; Detrusor; The work; The power