What is the role of reflex responses in the urologic management of neurologic disease?

Updated: Aug 08, 2019
  • Author: Frances M Dyro, MD; Chief Editor: Robert A Egan, MD  more...
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Answer

Baseline electrical activity in the sphincters can be modified by a number of maneuvers. The Credé maneuver (ie, pressing on the bladder suprapubically), the Valsalva maneuver, and stimulation of perianal or perineal skin all can produce reflex activation of the sphincters. Manual stimulation of the clitoris or the glans penis produces an increase in activity referred to as the bulbocavernosus reflex. This response has been quantified by using electrical stimulation to trigger the oscilloscope sweep and to activate the reflex.

Rushworth, in 1967, was the first to observe an EMG response to electrical stimulation of the pudendal nerve. [8] Since then, this response has been reported by several groups. The pudendal nerve can be stimulated by using ring electrodes around the penis in men or a bipolar stimulating probe on the clitoris in women. The stimulus is usually a square wave pulse with a duration of 0.05-0.2 msec and an amplitude of up to 300 V. Sensory threshold in healthy adults is 60-80 V. Stimulation is carried out at twice the sensory threshold.

When stimulation is applied in this way, a complex EMG response is recorded from the external urethral sphincter, with clear-cut components appearing and increasing in duration with increasing voltage. The first component to appear, R1, has a latency as long as 45 msec and a duration of 10-30 msec. This component decreases in latency as the voltage increases. A second component, R2, may occur at 50-120 msec at higher stimulating voltages. Some observers are able to distinguish a third component at about 140 msec in patients with intact spinal cords.

The first component of the sacral reflex is thought to represent an oligosynaptic or monosynaptic response at the level of 1 sacral segment. [9] The second component may be polysynaptic and involve several sacral segments. The third component probably represents a nociceptive response mediated centrally.

Attempts have been made to measure conduction velocities in the sensory and motor nerves.

Chantraine determined motor conduction velocities in the pudendal nerve using a technique quite difficult to apply in conventional EMG. [10] Pudendal motor latency is easier to measure by stimulating the pudendal nerve with a finger-mounted electrode placed against the ischial spine rectally. The sacral roots may be stimulated magnetically or by placing needle electrodes in the foramina. Somatosensory evoked potentials may be obtained by stimulating the perineum or the bladder neck and recording cortically.

Yilmaz et al have described a dartos reflex that is a sympathetically mediated scrotal reflex similar to the more commonly used cremasteric reflex. This evaluates the integrity of the T12-L2 sympathetics and the genitofemoral nerve. [11]


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