A non-invasive method for bladder electromyography in humans

No convincing correlation of bladder EMG in humans to simultaneously measured intravesical pressure has been reported in the literature. In most studies on bladder EMG the electrodes contact the bladder wall itself. This causes problems in the discrimination between very small extracellular signals, reflecting actual membrane potential changes of bladder muscle cells, and large electro-mechanical artefact caused by electrode movement as the tissue contracts. Aim of this study is to investigate whether bladder EMG can be performed non-invasively with Ag-AgCl surface electrodes that are placed on the abdominal skin of healthy volunteers. Bipolar electrode signals are obtained in a diagonal, vertical and horizontal direction of the abdominal electrodes. A conventional urodynamic investigation is performed according to International Continence Society standards simultaneously with bladder EMG. This new method shows that voiding is accompanied by a slow voltage change in bipolar electrode signals. The contribution of abdominal and other striated muscle activity to the bipolar electrode signals can clearly be distinguished from the slow voltage changes related to voiding. Free flowmetry shows that the electrical activity picked up by the abdominal electrodes is related to bladder emptying. In pressure/flow studies a relation between the electrical activity and the detrusor pressure is found. The present results suggest that the slow voltage changes found during bladder contraction are caused by summed membrane potential changes of bladder muscle cells, but this concept needs further testing. Also, validation for clinical use remains to be established.