Neurophysiological aspects of therapeutic sacral nerve root stimulation

Abstract

Neural control of lower urinary tract function can in principle sustain two basic activities - urine storage and emptying. It can be conceptualised to consist of control elements for determining: the thresholds for detrusor and sphincter activation; the gain adjustments for their function; the filter and switch mechanisms to control flow of information. Lower urinary tract dysfunction can be due to a dysfunctioning neural control even if there is no overt neurological disease. Electrical stimulation can be applied not only to substitute for lost neural control, but also for achieving a clinically relevant improvement of the dysfunctional lower urinary tract. Depolarisation of motor and sensory fibres in sacral roots leads to pelvic floor contraction and inhibition of the (active) detrusor, and it is considered that longer periods of such stimulation lead to pelvic floor muscle hypertrophy, changes in motor unit metabolism and other changes. It is postulated that there are perhaps even more important effects on the central nervous system which can be conceptualised as modifications of the dysfunctional neural control (i.e. “neuromodulation”).