Uroflowmetry: definition, procedure, indications and types

Definition:

•        Uroflowmetry is a simple, diagnostic screening procedure used to calculate the flow rate of urine over time.

•        The test is noninvasive (the skin is not pierced), and may be used to

  assess bladder and sphincter function.

 

 Uroflowmetry:

•        The measured urinary flow is a product of detrusor contractility and urethral resistance,in some cases modified by abdominal straining.

•        Even though uroflowmetry is not specific in identifying outlet obstruction ,the flow rate remains an extremely sensitive indicator of lower urinary tract symptoms.

•        Today most commercially available uroflowmeters are based on –

 1)Weight transducers, measuring voided volume and calculating flow rate by means of differentiation with respect to time.

 2) Rotating disc, measuring the power necessary to maintain a constant rotation ,where as urine tends to slow down the speed.

Procedure:

•        Uroflowmetry is performed by having a person urinate into a special funnel that is

   connected to a measuring instrument.

•         The measuring instrument calculates the amount of urine, rate of flow in seconds, and length of time until completion of the void. This information is converted into a graph and interpreted by a urologist.

•        The information helps to evaluate function of the lower urinary tract or help determine if there is an obstruction of normal urine outflow.

Indications :

•        1- Benign prostatic hypertrophy (BPH).

•        2-Cancer of the prostate, or bladder tumor.

•        3- Urinary incontinence - involuntary release of urine from the bladder.

•        4- Urinary blockage - obstruction of the urinary tract can occur for many reasons along any part of the urinary tract from kidneys to urethra. Urinary obstruction can lead to a back-flow of urine causing infection, scarring, or kidney failure if untreated. 
          5- Neurogenic bladder dysfunction - improper function of the bladder due to an alteration in the nervous system such as a spinal cord lesion or injury. 

          6- Frequent urinary tract infections (UTI’s).

   Uroflowmetry may be performed in conjunction with other diagnostic procedures, such as cystometry and cystography.

Uroflowmetry :

•        Properly performed uroflow rate determination should specify:

    - voided volume

    - patient environment and position

    - filling : by diuresis or by catheter

    - type of fluid voided

    - type of measuring equipment

    - solitary procedure or combined  with other measurements

Definitions :

•        Voided volume : The total volume of urine expelled from the bladder.

•        Residual urine volume : The total volume of urine remaining in the bladder after voiding.

•        Flow time : The time over which measurable flow actually occurs.

•        Maximum flow rate(Qmax): The maximum measured value of the flow rate.

•        Time to maximum flow : the elapsed time from the onset of flow to the point of maximum flow.

•        Mean flow rate(Qmean):  volume voided divided by flow time.

•        Continuous urinary flow : a constant urinary stream without interruption

Types of flow curve patterns

•        Type 1 : The normal flow curve is unbroken and bell shaped with only slight to moderate asymmetry of the bell.

   

•        Type 2: The prostatic curve is unbroken with pronounced asymmetry and an elongated ,flattened course from Qmax to end of voiding.

Type-2

   

•        Type 3 : The fluctuating flow curve is unbroken but characterized by greater fluctuations without reaching zero before the end of voiding.

•        Type 4 : The fractionated flow curve is discontinuous. 

•        Type 5 : The plateau flow curve is unbroken and a large part of the voided volume is voided by a constant Qmax.

Types 1,3,4,5

 Normal urinary flow:

 

•        The normal flow pattern is a continuous, bell-shaped, smooth curve with a rapidly increasing flow rate .

•        Because small voided volumes affect the curve shape and Qmax is volume dependent, only voided volumes of at least 150 ml should be interpreted .

•        The maximum flow rate should always be documented together with the total voided volume and post void residual volume with the following standard format: maximum flow rate/volume voided/post void residual volume.

•        Uroflow in men :

    Most consider Qmax greater than 15 to 20 ml/sec as normal and less than 10 ml/sec abnormal. These numbers decline with age by 1 to 2 ml/sec per 5 years. There is a decline in peak flow with age resulting in a maximum flow of 5.5 ml/sec at 80 years .

•        Uroflow in women :

   In the normal woman Qmax can be greater than 30 ml/sec, the flow curve is bell shaped as in men, and the flow time is shorter. Maximum flow in women does not seem to be dependent upon age.

 

Pitfalls:

•        Electronic analysis of uroflowmetry may introduce errors because the electronic device reads the absolute maximum value recorded by the machine and may read spikes on the curve that do not represent true flow .

•        Bladder over distension may be responsible for artifacts during uroflowmetry.

•        Another pitfall during uroflow evaluation is that of measuring only one flow parameter, such as peak flow.

Conclusion :

•        Accurate measurement of the urinary flow rate provides important and useful information that may indicate the presence of bladder outlet obstruction.

•        Careful examination of the flow pattern may indicate a possible etiology for an abnormal flow pattern.

•        The uroflow by itself, can neither diagnose bladder outlet obstruction nor predict which patients will benefit from surgery to relieve obstruction.

•        In view of its limitations ,in circumstances in which doubt remains after a uroflow study,further complex urodynamic studies are needed to identify the etiology of voiding dysfunction.