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PAEDIATRIC UROLOGY

11.1.6 Electromyography (emg) of the external sphincter

EMG is the study of electrical potentials generated by the depolarization of the external sphincter. For recording, skin surface electrodes are used in children, positioned left and right from the external anal sphincter. EMG should be interpreted in the light of the patient's symptoms, physical findings and urological and urodynamic investigations.

In normal subjects, there is a gradual increase in EMG activity from the pelvic floor during bladder filling; at the onset of micturition, there is complete absence of activity.

The finding of increased EMG activity during voiding, accompanied by simultaneous detrusor pressure and flow changes, is described by the term detrusor-sphincter dyssynergia (in neuropathic bladder/sphincter dysfunction) or detrusor-sphincter dysco-ordination (in neurologically normal children). Because of the many artefacts noted and the inability to distinguish electronic 'noise' from true EMG potentials on the recording, there is no consensus about using the EMG registration.

Table 19: Urodynamics: normal values in children

Storage phase

Maximum cystometric bladder capacity:

Age dependent (approx. age x 30)

Residual urine:

< 10 % of the bladder capacity

First desire to void:

Bladder filling > 60 % of the maximum bladder capacity

Intravesical pressure:

14 cmbbO at the beginning, up to 24 стНгО at the end of

the filling

Involuntary detrusor contraction:

None

Compliance:

> 25 т1_/стНгО

EMG:

Stable

Micturition phase (mictiometry)

Maximum urine flow:

Age dependent

Medium urine flow:

Age dependent

Micturition pressure:

< 75 стЬЮ (age dependent)

EMG:

Fluctuations

EMG = Electromyography