Functional modelling of voiding
(Modelvorming van de urinelozing)
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Urine is continuously produced in the kidneys. It is the function of the lower urinary tract to temporarily store the urine and expel it under appropriate circumstances.' A normal bladder has the ability to hold an increasing amount of urine without a significant increase in intravesical pressure, up to a certain volume. The concept of compliance was introduced to quantify this ability. The bladder neck and the urethra remain closed during the storage phase to maintain continence. As bladder filling progresses, a sensation of fullness gradually develops and an appropriate place to empty the bladder will be looked for. Voiding is initiated by relaxation of the pelvic floor, followed by an intravesical pressure rise and opening of the bladder neck and the urethra. The pressure rise is sustained until the bladder is empty.' The function of the lower urinary tract can be evaluated in a cystometric study.' In such a study, intravesical pressure is measured during controlled bladder filling and during voiding. The pressure that represents bladder function is that generated by the detrusor muscle. This so-called detrusor pressure is estimated by subtraction of the rectal pressure, which is used as a measure of intra-abdominal pressure, from the intravesical pressure. The flow rate during voiding is measured with a flowmeter. Additionally, pelvic floor activity is usually registered by means of electromyography.
- bladder volume
- urethral resistance relation