Functional magnetic stimulation of the spinal cord--a urodynamic study in healthy humans

To study the effects of functional magnetic stimulation of the spinal cord in healthy subjects on somatic and autonomic pathways innervating the anal and the external urethral sphincter, bladder, bladder neck, and rectum.

Eight healthy male volunteers gave their written informed consent and underwent functional magnetic stimulation of the thoracolumbar and sacral spinal cord. A two-channel microtip pressure transducer catheter was placed rectally measuring the abdominal and anal sphincter pressure. A three-channel microtip pressure transducer catheter was inserted into the urethra measuring the bladder, the bladder neck, and the external urethral sphincter pressure. A comprehensive protocol of single and repetitive magnetic stimulations was performed. Frequency, location, and duration of stimulation were varied while the intensity of stimulation was adapted to the maximum the subjects could tolerate. In four subjects, the degree of bladder filling was changed and the protocol was repeated when the subjects reported a full bladder and desire to void.

Continuous magnetic stimulation of the thoracolumbar spinal cord and the sacral roots applied with different frequencies (5, 15, 30, 60, 100 Hz) and different duration of stimulation (10, 30, 120 sec) evoked sphincter contraction of both anal and urethral sphincters. The stimulation could not evoke contractions of the bladder, the bladder neck, or the rectum. Also with filled bladder and present desire to void, the magnetic stimulation could not activate autonomic pathways innervating these structures.

Considering our results, we suggest that in individuals with preserved sensibility magnetic stimulation of the spinal cord with intensities below the pain threshold is ineffective in activating autonomic nerve fibres innervating bladder, bladder neck, and rectum.