title: What is the relationship between free flow and pressure flow studies in women?
abstract: OBJECTIVE
  The relationship between free flow (FFS) and pressure flow (PFS) voiding studies remains uncertain and the effect of a urethral catheter on flow rates has not been determined. The relationship between residuals obtained at FF and PFS has yet to be established.
  
  
  METHODS
  This was a prospective cohort study based on 474 consecutive women undergoing cystometry using different sized urethral catheters at different centres. FFS and PFS data were compared for different conditions and the relationship of residuals analysed for FFS and PFS. The null hypothesis was that urethral catheters do not produce an alteration in maximum flow rates for PFS and FF studies.
  
  
  RESULTS
  Urethral catheterisation results in lower flow rates (p < 0.01) and this finding is confirmed when flows are corrected for voided volume (p < 0.01). FFS and PFS maximum flow rates are lower in women with DO than USI (p < 0.01). A 6-F urethral catheter does not have a significantly greater effect than a 4.5-F urethral catheter. A mathematical model can be applied to transform FFS to PFS flow rates and vice versa. There was no significant difference between the mean residuals of the two groups (FFS vs PFS-two-tailed t = 0.54, p = 0.59). Positive residuals in FFS showed a good association with positive residuals in the PFS (r = 0.53, p < 0.01)
  
  
  CONCLUSIONS
  Urethral catheterisation results in lower maximum flow rates. The relationship can be compared mathematically. The null hypothesis can be rejected.
authors: Department of Obstetrics and Gynaecology, Medway NHS Foundation Trust, Windmill Road, Gillingham, Kent ME7 5NY, UK. jraduckett@hotmail.com
authors: Jonathan
authors: J
authors: Duckett
authors: Katherine
authors: K
authors: Cheema
authors: Avanti
authors: A
authors: Patil
authors: Maya
authors: M
authors: Basu
authors: Sian
authors: S
authors: Beale
authors: Brian
authors: B
authors: Wise
mesh_terms: D015331:Cohort Studies; D005260:Female; D006801:Humans; D011312:Pressure; D011446:Prospective Studies; D014546:Urinary Catheterization; D062885:Urinary Catheters; D014554:Urination / Q000502:physiology*; D014563:Urodynamics / Q000502:physiology*