title: Experimental and clinical trial of measuring urinary velocity with the pitot tube and a transrectal ultrasound guided video urodynamic system.
abstract: BACKGROUND
  The pitot tube is a common device to measure flow velocity. If the pitot tube is used as an urodynamic catheter, urinary velocity and urethral pressure may be measured simultaneously. However, to our knowledge, urodynamic studies with the pitot tube have not been reported. We experimentally and clinically evaluated the feasibility of the pitot tube to measure urinary velocity with a transrectal ultrasound guided video urodynamic system.
  
  
  METHODS
  We carried out a basal experiment measuring flow velocity in model urethras of 4.5-8.0 mm in inner diameter with a 12-Fr pitot tube. In a clinical trial, 79 patients underwent transrectal ultrasound guided video urodynamic studies with the 12-Fr pitot tube. Urinary velocity was calculated from dynamic pressure (Pd) with the pitot tube formula and the correcting equation according to the results of the basal experiment.
  
  
  RESULTS
  Velocity measured by the pitot tube was proportional to the average velocity in model urethras and the coefficients were determined by diameters of model urethras. We obtained a formula to calculate urinary velocity from the basal experiment. The urinary velocity could be obtained in 32 of 79 patients. Qmax was 8.1 +/- 4.3 mL/s (mean +/- SD; range, 18.4-1.3 mL/s), urethral diameter was 7.3 +/- 3.0 mm (mean +/- SD; range, 18.7-4.3 mm) and urinary velocity was 69.4 +/- 43.6 (mean +/- SD; range, 181.3-0 cm/s) at maximum flow rate. The correlation coefficient of Qmax measured by a flowmeter versus Qdv flow rate calculated with urethral diameter and velocity was 0.41 without significant difference.
  
  
  CONCLUSIONS
  The use of the pitot tube as an urodynamic catheter to a transrectal ultrasound-guided video urodynamic system can measure urethral pressure, diameter and urinary velocity simultaneously. However, a thinner pitot tube and further clinical trials are needed to obtain more accurate results.
authors.affiliation: Department of Urology, Sento Hospital, Osaka, Japan. jyukio.tujimoto@nifty.ne.jp
authors.forename: Yukio
authors.initials: Y
authors.lastname: Tsujimoto
authors.forename: Yorihito
authors.initials: Y
authors.lastname: Nose
authors.forename: Kenkichi
authors.initials: K
authors.lastname: Ohba
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D002404:Catheterization / Q000295:instrumentation*; D005240:Feasibility Studies; D006801:Humans; D008297:Male; D008365:Manometry; D008433:Mathematics; D008875:Middle Aged; D008953:Models, Anatomic; D012828:Silicones; D014160:Transducers, Pressure; D014463:Ultrasonography; D014521:Urethra / Q000000981:diagnostic imaging*; D014563:Urodynamics / Q000502:physiology*; D014741:Video Recording
chemical_list: D012828:Silicones