Purpose: Concentric needle and current transurethral surface recording techniques are unlikely to accurately record electromyography activity of the male striated urethral sphincter during dynamic tasks. Thus, we developed a novel transurethral surface electrode that could be fixed to the urethral mucosa with optimal orientation to record striated sphincter electromyography.
Materials and methods: Four recording surfaces were placed at equal intervals circumferentially around the tip of a 6Fr pediatric urinary catheter. This configuration provides optimal electrode-to-muscle fiber orientation for differential amplification. The electrode was fixed by gentle suction via the urine ports. Intra-abdominal pressure was monitored with a gastric pressure transducer. Five healthy male subjects participated in the validation study. Electromyography recordings were made of voluntary and involuntary striated sphincter contractions to investigate the quality of recordings and electrode stability. Tasks included maximal voluntary contractions of the striated sphincter and intra-abdominal pressure, submaximal contractions, ramped intra-abdominal pressure efforts and voluntary coughs.
Results: Data indicated high quality electromyography recordings. Energy in the frequency spectrum was between 50 and 500 Hz, typical of human striated muscle surface electromyography. The median signal-to-noise ratio was 16.1 db (range 11.9 to 18.6) for striated sphincter maximal voluntary contractions. Motor unit action potentials could be discriminated during gentle contractions. Overlaid motor unit action potentials showed consistent morphology. Energy associated with motion artifact during a cough was less when suction was applied, indicating improved electrode stability.
Conclusions: The new electrode provides high quality surface electromyography recordings of the male striated sphincter during dynamic tasks, such as coughing.