Define urodynamics
Measuring the properties of the bladder for diagnostic purposes
Define uroflowmetry
Measurement of flow rate during voiding
Where can uroflowmetry occur
Clinical
Home
Most common method of clinical uroflowmetry
Gravimetric Flowmeter
Gravimetric Flowmeter
- scales to record the mass vs time
- jug and funnel above scales which patient voids into
- in a clinic
- commode
Units of flow rate
Q (m/s)
How to calculate flow rate?
Differentiate voided volume in respect to time
Key parameters that are good to know?
QMAX = Maximum flow rate
Void Time
Area under curve = voided volume
Shapes of graph = different pathologies sometimes
Artefacts of gravimetric uroflowmetry technique?
- waggle artefact = in men if urine stream is waggled around, can change flow rate instead of straight down
- differentiation = noise
- abdominal straining = increasing abdominal pressure, can mask low flow rate caused by obstruction for example
Advantages of Spinning disc flow meter
- to provide faster temporal resolution
- no differentiation = less noise
How does a Spinning disc flow meter work?
- rota turned by an electrical motor
- turned at a constant rpm (revelutions per minute)
- individual voids into motor and urine stream slows the motor
- motor therefore needs more power to turn at same constant rpm against urine stream
- motor draws more current to turn urine = increased electrical current which is proportional to the flow rate
Why isn’t a spinning disc flow meter used anymore?
In practice, advantages of detecting quick changes in flow rate were not clinically useful
Urine drop spectroscopy Method
- urine stream comes down and breaks down into drops
- drops are assumed to be spherical
- camera system measures number and diameter of drops
- this is used to show flow rate over time
Pros and Cons of urine drop spectroscopy
- no differentiation = no noise
- additional problems of cleaning after use
What is the normal QMax?
20ml/s
What graph changes will you see during an obstruction?
- Lower QMax (flow rate)
- Longer void time
- Same area under the curve if voiding the same volume
What is a clinically reduced QMax?
<10ml/s
What is QMax dependent on?
- bladder volume
- at very low volumes = QMax is low
- at high volumes = QMax increased
- at very high = QMax drops
How do you know a low flow rate is caused by obstruction or problems with the detrusor muscle/nerves?
- we don’t know
- need to use cystometrogram/ pressure flow studies
What is a cystometrogram?
Measuring flow rate as well as pressures in the bladder
Advantages of home uroflowmetry over clinical?
- patient voiding in their own setting so no shy bladder/ white coat syndrome/ inhibition
- can have multiple voids so not relying on a single void measurement (more representative)
- can record voids throughout the day = better data along with a voiding diary
- voided volume likely to be more physiological so QMax not dependent on flow volume
Disadvantage of home uroflowmetry
- only able to measure QMax, not flow vs. time
- issues of patient compliance/can they use device correctly
Stream Test Device
- home method
- plastic beaker
- at bottom is tiny few mm diameter hole
- mainly for men for BPH/prostate cancer diagnosis/monitoring
- void into cup, urine fills up and flows out at the same time through hole
- height of urine goes up and reaches maximum height in cup
- flow rate = flow out of the cup
- if we measure the height that the urine goes up can estimate QMax
- cup has indicator line = QMax of 10ml/s, if urine over it then they are fine, if not then they have low flow rate
UFlow Device
- home method
- void into the top
- hole at the bottom
- 3 different chambers
- chambers give 3 different measurements
- middle = 10-15ml/s
- lower = less than 10 ml/s
- upper = 15ml/s
- different diameters in each chamber = greater change in height for QMax if tube is very narrow, little change in height for QMax if very wide tube
- so widest at top = we don’t care if normal >15ml/s
- narrower diameter at bottom as <10ml/s and want to be accurate of flow rate
