Uroflowmetry
Urine
flow studies are the simplest of
urodynamic techniques – noninvasive
Equipment is simple and relatively
inexpensive
Definitions
Urineflow - described in terms of flow rate
and flow pattern (continuous or
intermittent)
Flow rate - volume of fluid expelled via the
urethra per unit time and is expressed
in ml/s
Maximum flow rate (Qmax) - Maximum measured value
of the flow rate
Voided volume (VV) - Total volume expelled via the
urethra
Flow time - Time over which measurable flow occurs
Average flow rate (Qave) - Voided volume divided by
flow time
Time to maximum flow - Elapsed time from onset of flow
to maximum flow
Voiding time - total duration of micturition, including the
interruptions
Intermittent flow - same measurements
are used as for continuous flow curve
However, flow time must be measured
carefully, as the time intervals between
flow episodes are disregarded
NORMAL CURVE
INTERMITTENT PATTERN
Equipment
Weight Transducer Flowmeter
Rotating Disc Flowmeter
Capacitance Flowmeter
Weight transducer flowmeter involves
weighing the urine voided
Calculates the urine flow rate by
differentiation with respect to time
Rotating-disc flow meter
Spinning disc on which the urine falls
The disc is kept rotating at the same speed by a
servomotor, in spite of changes in the urine flow rate
(weight of the urine tends to slow the rotation of the disc)
The differing power needed to keep disc rotation
constant is proportional to the urine flow rate
Normal Flow Patterns
When considering the normal flow rates
Age and Sex
Voided volume
should be taken into account
In addition to numerical data , shape of
the trace - important
Normal flow
“Bell” shape
Maximum flow is reached in the first 30% of any trace
and within 5 seconds from the start of flow
Flow rate varies according to the volume voided
The final phase of a normal flow trace shows a rapid fall
from high flow, sharp cutoff at the termination of flow
Urine flow rate is highly dependent on the volume voided
Detrusor muscle when stretched achieves an optimal
performance, but if stretched further it becomes
inefficient
At more than 400 ml, the efficiency of the detrusor
begins to decrease and Qmax is lower
Flow rates are highest and most predictable in the
volume range between 200 ml and 400 ml
Qmax Vs Voided Volume
Flow rate nomograms
Siroky nomogram
Bristol nomogram
Siroky Nomogram
Abnormal Flow Patterns
Urine flow results from the interaction
between the detrusor contraction /
abdominal straining and urethral
resistance
urine flow rates have limitations
which must be appreciated
Information from urine flow traces, without simultaneous
pressure recording must be interpreted with care
Misleading situations
Patients with normal flow can have bladder outlet
obstruction when a normal Q max is maintained by
abnormally high voiding pressures
Patients whose low flow rates are due to detrusor
underactivity rather than to bladder outlet obstruction
Bladder Outlet Obstruction (BOO)
Low Qmax and reduced average flow, with the
average flow greater than half the Qmax
Qmax- obtained quickly (3–10 secs), but the flow
rate then decreases slowly
Terminal dribble
Obstruction may be
Compressive - Benign Prostatic Obstruction
Constrictive - Urethral Stricture
Constrictive obstruction - “plateau”-shaped trace with
little change in flow rate and little difference between
Qmax and Qave
Compressive obstruction - first third of the flow trace
may appear relatively normal, Qmax will be reduced,
latter part is elongated into a pronounced “tail” of
reducing flow rate
URETHRAL STRICTURE
BENIGN PROSTATIC OBSTRUCTION
Detrusor Underactivity (DUA)
Symmetrical trace with a low maximum flow
rate is seen
Time to reach Qmax is variable , may occur in the
second half of the trace
Considerable overlap between - obstructed and
underactive detrusor group – proof comes from a
pressure-flow study
DETRUSOR UNDERACTIVITY
Detrusor Overactivity
Very high maximum flow rates in abnormally short time
(1 s - 3 s)
Reduction in time to Qmax is achieved because the
detrusor contraction has already opened the bladder
neck widely, hence reducing the urethral resistance.
DETRUSOR OVERACTIVITY
Interrupted Flow Patterns
Irregular Trace
Secondary to
Straining
Habitual
Obstruction
DO
Urethral overactivity
Artefacts
Artefacts
“Cruising”
Caused by men moving their stream in relation to the
central exit from the collecting funnel
“Peaks” occur when the point of impact of the stream is
moving down the side of the funnel towards the central
exit
“Valleys” occur when the impact point is moving
away from the exit
CRUISE ARTEFACT
“Squeezing”
In an effort to deny the onset of age (and reducing urine
flow), some men have the habit of squeezing the tip of
their penis or foreskin during voiding
This leads to a series of peaks
When the patient is asked to stop this , the flow trace
usually becomes classically obstructed, and the flow rate
is no longer within the normal range
SQUEEZE ARTIFACT
Indications
Urine flow studies are an excellent screening study in a
wide variety of patients
But they must be followed by pressure-flow studies -
precise definition of bladder and urethral function
Uroflow is used to investigate possible bladder
outlet obstruction and can also give a guide to detrusor
contractility
It can be used for patients of all ages and both sexes
Uroflow is the screening test of choice in men of
all ages with symptoms suggestive of outlet
obstruction
Uroflow should be measured before and after
any procedure designed to modify the function
of the outflow tract
Qmax is below 10 ml/s then the chance of the
patient having BOO is 90%
If the Qmax is 10 ml/s to 15 ml/s then the
incidence of BOO is 71% or less
Because 29% of these patients will not have
BOO, patients with a Qmax of 10 ml/s or more
should have PFS before invasive therapy
AUA Guidelines
Urinary flow rate measurement is optional
It is useful in the initial diagnostic assessment and during
or after treatment to confirm response
Despite the noninvasive nature of the test and its clinical
value, it is an optional test before embarking on any
invasive therapy
AUA Guidelines
Peak urinary flow (Qmax) is the best single measure to
estimate the probability of a patient to be urodynamically
obstructed
But a low Qmax does not distinguish between
obstruction and decreased detrusor contractility
Because of the intra‐individual variability and the volume
dependency of the Qmax, at least
2 flow rates should be obtained, ideally both with a
volume greater than 150 mL voided urine.
THANK U
