LETTER TO THE EDITOR

Comment on “Recording the EvokedCanine Detrusor Electromyogram,”Neurourol Urodynam 1999;18:687–95

To the Editor:

I read with interest this paper, which aims to correlate the detrusor electomyo-gram (EMG) with changes in intravesical pressure during bladder stimulation. Thisapproach, together with their attempt to control for extraneous artifact and recordingthe stimulus on the same time scale as changes in intravesical pressure and electricalactivity, represents an advance on recently published work on the subject of detrusorEMG. The authors used spectral density analysis to isolate different frequency spectraof their recordings and found that detrusor contraction correlated most clearly withsignals above 3 Hz. They infer from their experiments that smooth muscle EMGrecordings from animal detrusor smooth muscle are possible.

However, while recognising the difficulties associated with discriminating be-tween EMG activity and artifact from tissue and fluid movements under the electrodetip, no methodological advances to verify these signals as extracellularly recordedrepresentations of changes in intracellular electrical activity during contraction havebeen made. The authors, although stating the need for further investigations, onlypresume that the lower frequency signals detected during detrusor contraction areartifact and that the high-frequency spike activity detected at the beginning of theintravesical pressure rise represents EMG activity.

Accurate and reproducible recordings of the detrusor EMG have eluded us fornearly 50 years. In fact, one may question whether extracellular recording of EMGactivity from any smooth muscle has been proven to be authentic beyond a doubt. Theincreasing amount of interest in recording the real detrusor EMG relates to theever-increasing potential applications of this technique to fundamental questions insmooth muscle physiology, clinical urology, and pharmacology. Any extracellularrecording of detrusor smooth muscle electrical activity must therefore be provedunequivocally to be of EMG origin before progressing further, and until the criteriathat were set out by Craggs [1998] have been met, the nature of the real detrusor EMGremains unproven.

A. BallaroInstitute of Urology and NephrologyRoyal Free and University College Medical SchoolUniversity College of LondonLondon, United Kingdom

Neurourology and Urodynamics 19:713–714 (2000)

© 2000 Wiley-Liss, Inc.

PROD #2032

REFERENCE

Craggs MD. 1998. Editorial comment: the elusive electromyogram: fact vs artifact. Neurourol Urodynam17:80–1.

AUTHORS’ REPLY

We read with interest the comment of Dr. Ballaro on our article concerning thedetrusor EMG. We are aware that the recorded activity from the detrusor muscle hasnot been unequivocally proven. On the other hand, the presented study is definitely adecisive step toward the elucidation of the true detrusor EMG—a clear correlation ofhigh-frequency activity with changes in intravesical pressure was observed. From themethodological point of view, the discrimination between extracellularly recordedsignals and artifact from tissue movement is notoriously difficult. Detrusor smoothmuscle contraction is a relatively slow process in comparison with electrophysiologi-cal changes in a smooth muscle cell. Therefore, we believe that the recorded spikeactivity is electrical activity rather than movement artifact. We hope to confirm thishypothesis by various trials in our laboratory, but further investigations are requiredto prove the authenticity of the detrusor EMG. One possibility is to activate pharma-comechanical-coupling mechanisms of the muscle cell. The result is muscle contrac-tion without membrane depolarization. Under these circumstances, discriminationbetween EMG activity and artifact from tissue movement might be possible.

Jeroen ScheepeKlaus-Peter JunemannDepartment of UrologyKlinikum MannheimUniversitatsklinikumMannheim, Germany

714 Letter to the Editor