The real bladder electromyogram.

The nature of bladder electrical activity was investigated in anaesthetised cats and 1 baboon. A time-locked muscle response to sacral ventral root stimulation was most clearly detected within a 10-40 Hz frequency band, the response preceding the rise in intravesical pressure. During reflex voiding only activity in the 10-40 Hz band was consistently related to reflex voiding and to the small contractions leading up to voiding. It is concluded that only a very limited part of the wide band electrical activity recorded from the bladder can be considered genuine electromyogram and that the 10-40 Hz frequency band probably excludes the worst of the artefact. Possible sources of artefact and their relation to changes in intravesical pressure are presented in Table I.