LONDON: The shape of a man’s urine stream can help diagnose urinary problems such as an enlarged prostate, show results from a British study.
The researchers found that healthy men had characteristic spiral shaped urine streams, the specific formation of which correlated with their maximum flow rate.
“By applying a novel computational fluid dynamics method we are able to demonstrate for the first time that the shape of the urine stream can be used as a diagnostic tool for medical practitioners,” said aerodynamics researcher Andrew Wheeler from University of Southampton, and lead author of the study published in the journal PLoS One.
“This work is important both from a practical perspective for medical practitioners and as a fundamental study of bio-fluid mechanics,” he added.
How fast can you urinate?
Uroflowmetry, or the study of urine flow rate, has been used to help diagnose a wide range of urinary conditions including neuromuscular pathologies and bladder outlet obstruction for the past 50 years.
As a result of this, a variety of procedures have been developed to allow measurement of urine flow ranging from gravimetric methods, involving weighing of urine, to more complex rotating disc-flow metering, where the weight of urine falling onto a spinning disc allows measurement of flow rate.
However, despite the long history of uroflowmetry, no studies to date have investigated whether the characteristic shape or wave pattern of urine as it exits the urethral opening or meatus could have diagnostic implications for physicians.
Wheeler and team demonstrated that the wave pattern of male urine can be used diagnostically in a group of men with and without low urine flow rate and that it reflects both the shape of the urethral opening and the flow rate.
“A commonly held misconception is that the shape of the male urine stream is to do with the spiralling shape of the male urethra,” commented Wheeler.
“In fact we show that the characteristic pattern formed by the urine stream is due to a surface-tension phenomenon that depends on both the flow-rate and the shape of urethral exit.”
On the right wavelength
To test the theory that urine shape may be diagnostic, Wheeler and colleagues first modelled the shape of a possible urine stream issuing from a number of different shaped orifices on a computer, before confirming their findings using a video taken of a volunteer’s urine stream.
They found that for a healthy shaped urethral opening the ‘wavelength’ – distance from the meatus to the first ‘pinch point’ in a urine stream shaped like a repeating figure of eight or hourglass – was directly and positively related to the flow rate of urine, as measured using a clinical urine flow meter.
“These two parameters can be used to determine poor flow rate and urethral dilation; low flow rate is currently used as the main indicator for underlying urological problems and poor urethral dilation can be a result of urethral atrophy or constriction,” said Wheeler.
To test the applicability of their computational and experimental model, Wheeler and co-investigators recruited 60 healthy volunteers (average age 26 years) and 60 men with urinary flow problems (average age 67 years) to take part in a comparative study.
The men were asked to estimate the maximum wavelength of their urine flow in millimetres and measure their peak flow rate into a urine flow meter.
For the healthy volunteers, there was a significant positive correlation between peak flow rate and their estimated maximum wavelength. But, no such association was seen for the men with urine flow problems who showed substantial variation in these measures from person to person.
Study co-author Martin Knight, from Queen Mary, University of London, said: “The computer model matched perfectly to experiments in the laboratory and also with video data of human volunteers. There was an excellent correlation between the shape of the urine stream and the urine flow rate.”
The shape of the future
“On its own this technique cannot diagnose whether a low flow rate is caused by an obstruction in the urethra or problems in the bladder muscle. Nor can it determine whether any obstruction is due to an enlarged prostate or other problems,” explained Wheeler.
“However the technique may be useful for monitoring a patient over an extended period of time,” he added. For example, it could be used to assess the efficacy of medication given to patients to reduce the size of an enlarged prostate.
“This research began as a student project when a team of urologists asked Queen Mary to come up with a simple non-invasive way of measuring urine flow rate that could be easily used at home where patient’s urine flow rates are likely to be more typical than when urinating in hospital,” remarked Knight.
“The current techniques, although very accurate, are difficult or expensive to use reliably outside of the clinic. This new approach may therefore represent a useful solution to this important medical engineering problem, allowing men to easily monitor their urine flow rate.”
Abstract of the paper, published in PLoS One: “The Shape of the Urine Stream — From Biophysics to Diagnostics”