title: Pressure decay half-life: a method for characterizing upper urinary tract urine transport.
abstract: OBJECTIVE
  We examined the pressure dynamics of hydronephrotic kidneys after elevated renal pelvic pressure developed.
  
  
  METHODS
  A total of 40 patients (44 renal units) 0.2 to 12 years old was evaluated. Transiently elevated renal pelvic pressure was induced with a percutaneous nephrostomy infusion. After renal pelvic pressure increased the infusion was stopped and the subsequent decrease in pressure with time was plotted as a pressure decay curve. The rapidity of the decrease in renal pelvic pressure was then quantitated as a half-life for each pressure decay curve. Pressure decay half-lives were compared to corresponding pressure flow study results and diuretic nuclear renography half-lives.
  
  
  RESULTS
  Renal units without elevated renal pelvic pressure during infusion at a high physiological flow rate were associated with relatively rapid pressure decay, whereas those with elevated renal pelvic pressure during infusion were associated with much slower pressure decay (p < 0.0001). Diuretic nuclear renography half-lives had no correlation with collecting system pressure dynamics.
  
  
  CONCLUSIONS
  Pressure decay half-life provides an objective quantitative measure of the relative tendency for elevated renal pelvic pressure to persist. When used in conjunction with other diagnostic modalities, it may be a useful parameter for a comprehensive assessment of the risk of pressure induced injury in hydronephrotic kidneys.
authors.affiliation: Department of Surgery (Division of Urology), Hospital for Sick Children, Toronto, Ontario, Canada.
authors.forename: L C
authors.initials: LC
authors.lastname: Fung
authors.forename: A E
authors.initials: AE
authors.lastname: Khoury
authors.forename: G A
authors.initials: GA
authors.lastname: McLorie
authors.forename: P G
authors.initials: PG
authors.lastname: Chait
authors.forename: B M
authors.initials: BM
authors.lastname: Churchill
mesh_terms: D002648:Child; D002675:Child, Preschool; D006207:Half-Life; D006801:Humans; D006869:Hydronephrosis / Q000000981:diagnostic imaging / Q000503:physiopathology*; D007223:Infant; D007682:Kidney Pelvis / Q000000981:diagnostic imaging / Q000503:physiopathology*; D011312:Pressure; D011866:Radioisotope Renography; D013997:Time Factors; D014556:Urine; D014563:Urodynamics