Experimental and clinical trial of measuring urinary velocity with the pitot tube and a transrectal ultrasound guided video urodynamic system.
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.
Tsujimoto
Yukio
Y
Department of Urology, Sento Hospital, Osaka, Japan. jyukio.tujimoto@nifty.ne.jp
Nose
Yorihito
Y
Ohba
Kenkichi
K
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
D012828:Silicones