title: Work Capacity of the Bladder During Voiding: A Novel Method to Evaluate Bladder Contractile Function and Bladder Outlet Obstruction.
abstract: BACKGROUND
  Work in voiding (WIV) of the bladder may be used to evaluate bladder status throughout urination rather than at a single time point. Few studies, however, have assessed WIV owing to the complexity of its calculations. We have developed a method of calculating work capacity of the bladder while voiding and analyzed the associations of bladder work parameters with bladder contractile function and bladder outlet obstruction (BOO).
  
  
  METHODS
  The study retrospectively evaluated 160 men and 23 women, aged >40 years and with a detrusor pressure at maximal flow rate (PdetQmax) of ≥40 cmH2O in men, who underwent urodynamic testing. The bladder power integration method was used to calculate WIV; WIV per second (WIV/t) and WIV per liter of urine voided (WIV/v) were also calculated. In men, the relationships between these work capacity parameters and PdetQmax and Abrams-Griffiths (AG) number were determined using linear-by-linear association tests, and relationships between work capacity parameters and BOO grade were investigated using Spearman's association test.
  
  
  RESULTS
  The mean WIV was 1.15 ± 0.78 J and 1.30 ± 0.88 J, mean WIV/t was 22.95 ± 14.45 mW and 23.78 ± 17.02 mW, and mean WIV/v was 5.59 ± 2.32 J/L and 2.83 ± 1.87 J/L in men and women, respectively. In men, WIV/v showed significant positive associations with PdetQmax (r = 0.845, P = 0.000), AG number (r = 0.814, P = 0.000), and Schafer class (r = 0.726, P = 0.000). Conversely, WIV and WIV/t showed no associations with PdetQmax or AG number. In patients with BOO (Schafer class > II), WIV/v correlated positively with increasing BOO grade.
  
  
  CONCLUSIONS
  WIV can be calculated from simple urodynamic parameters using the bladder power integration method. WIV/v may be a marker of BOO grade, and the bladder contractile function can be evaluated by WIV and WIV/t.
authors.affiliation: Department of Urology, Beijing Jishuitan Hospital, Beijing 100035, China.
authors.forename: Ning
authors.initials: N
authors.lastname: Liu
authors.forename: Li-Bo
authors.initials: LB
authors.lastname: Man
authors.forename: Feng
authors.initials: F
authors.lastname: He
authors.forename: Guang-Lin
authors.initials: GL
authors.lastname: Huang
authors.forename: Ning
authors.initials: N
authors.lastname: Zhou
authors.forename: Xiao-Fei
authors.initials: XF
authors.lastname: Zhu
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009119:Muscle Contraction / Q000502:physiology; D012189:Retrospective Studies; D001743:Urinary Bladder / Q000502:physiology*; D001748:Urinary Bladder Neck Obstruction / Q000503:physiopathology*; D014563:Urodynamics / Q000502:physiology