Detrusor-sphincteric dyssynergia in paraplegics compared with the synergia in a brain-dead human by using the single-fibre action potential recording method

Anorectal motility responses to selective stimulation of the ventral sacral nerve roots in an experimental model

Background

Control of defaecation and continence may be lost in patients with spinal cord injury. Electrical stimulation of sacral nerve roots to promote defaecation simultaneously activates both the rectum and the external anal sphincter (EAS), and may actually obstruct defaecation. The aim of this study was to investigate whether the EAS could be blocked selectively by selective stimulation of the ventral sacral nerve roots, and whether activation of the rectum without activation of the EAS could be obtained by stimulation of the ventral sacral nerve roots.

Methods

Selective electrical stimulation was performed using anodal blocking, a tripolar cuff electrode and monophasic rectangular current pulses applied to the sacral nerve roots in nine Göttingen minipigs.

Results

Simultaneous responses in the rectum and the anal canal were observed in five animals, whereas only anal responses were noted in four. Variations in cross-sectional area and an increase in rectal pressure seemed to facilitate defaecation. Without blocking, the increase in anal canal pressure was 16–45 cmH2O. With blocking, this increase was abolished in seven and reduced to 3–6 cmH2O in two animals.

Conclusion

Selective activation of the rectum is possible using an anodal block of somatic motor fibres. This technique holds promise in further development of electro-defaecation.

Detrusor-sphincteric dyssynergia in humans with spinal cord lesions may be caused by a loss of stable phase relations between and within oscillatory firing neuronal networks of the sacral micturition center

(1) Single-fibre action potentials (APs) were recorded with 2 pairs of wire electrodes from lower sacral nerve roots during surgery in patients with spinal cord lesions and in a brain-dead human. Conduction velocity distribution histograms were constructed for afferent and efferent fibres, nerve fibre groups were identified and simultaneous impulse patterns of alpha and gamma-motoneurons and secondary muscle spindle afferents (SP2) were constructed. Temporal relations between afferent and efferent APs were analysed by interspike interval (II) and phase relation changes. (2) In a paraplegic with hyperreflexia of the bladder, urinary bladder stretch (S1) and tension receptor afferents (ST) fired already when the bladder was empty, and showed a several times higher bladder afferent activity increase upon retrograde bladder filling than observed in the brain-dead individual. Two alpha 2-motoneurons (FR) innervating the external bladder sphincter were already oscillatory firing to generate high activity levels when the bladder was empty. They showed activity levels with no bladder filling, comparable to those measured at a bladder filling of 600 ml in the brain-dead individual. A bladder storage volume of 600 ml was thus lost in the paraplegic, due to a too high bladder afferent input to the sacral micturition center, secondary to inflammation and hypertrophy of the detrusor. (3) In a brain-dead human, 2 phase relations existed per oscillation period of 160 ms between the APs of a sphincteric oscillatory firing alpha 2-motoneuron, a dynamic fusimotor and a secondary muscle spindle afferent fibre. Following stimulation of mainly somatic afferent fibres, the phase relations changed only little. (4) In a paraplegic with dyssynergia of the urinary bladder also 2 phase relations existed per oscillation period of 110 ms in a functional unit between the APs of a sphincteric alpha-motoneuron, a fusimotor and a secondary spindle afferent fibre. The phase relations changed with time following stimulation of mainly somatic afferents. A second functional unit organized by phase-related interactions was phase related to the first functional unit. (5) Following painful bladder catheter pulling, the parasympathetic division was transiently activated several times in the paraplegic. At times of activation of the parasympathetic division, 3 broad phase relations occurred within and between the two functional units, indicating that the parasympathetic division in the sacral micturition and defecation center channeled an additional input to the somatic oscillatory firing neuronal networks driving motoneurons which innervate the external bladder and/or anal sphincters.

Classification of human peripheral nerve fibre groups by conduction velocity and nerve fibre diameter is preserved following spinal cord lesion

(1) Single nerve fibre action potentials (APs) of lower sacral nerve roots were recorded extracellularly with two pairs of wire electrodes during an operation in which an anterior root stimulator for bladder control was implanted in 9 humans with a spinal cord lesion and dyssynergia of the urinary bladder. Roots that were not saved and that were used to record from were later used for morphometry. (2) Nerve fibre groups were identified by conduction velocity distribution histograms of single afferent and efferent fibres and partly by nerve fibre diameter distribution histograms, and correlation analysis was performed. Group conduction velocity values were obtained additionally from compound action potentials (CAPs) evoked by electrical stimulation of nerve roots and the urinary bladder. (3) The group conduction velocities and group nerve fibre diameters had the following pair-values at 35.5 degrees C: Spindle afferents: SP1 (65 m/s/13.1 microns), SP2 (51/12.1); touch afferents: T1 (47/11.1), T2 (39/10.1), T3 (27/9.1), T4 (19/8.1); urinary bladder afferents: S1 (41 m/s/-), ST (35/-); alpha-motoneurons: alpha 13 (-/14.4), alpha 12 (65m/s/13.1 microns), alpha 11 (60?/12.1)(FF), alpha 2 (51/10.3)(FR), alpha 3 (41/8.2)(S); gamma-motoneurons: gamma beta (27/7.1), gamma 1 (21/6.6), gamma 21 (16/5.8), gamma 22 (14/5.1); preganglionic parasympathetic motoneurons: (10 m/s/3.7 microns). (4) The values of group conduction velocity and group nerve fibre diameter measured in the paraplegics were very similar to those obtained earlier from brain-dead humans and patients with no spinal cord lesions. Also, the number and the density of myelinated fibres were preserved in the roots. Thus, the classification and identification of nerve fibre groups remained preserved following spinal cord lesion. A direct comparison can thus be made of natural impulse patterns of afferent and efferent nerve fibres between paraplegics (pathologic) and brain-dead humans (supraspinal destroyed CNS, in many respects physiologic). (5) When changing the root temperature from 32 degrees C to 35.5 degrees C, the group conduction velocities changed in the following way in one case: SP2: 40 m/s (32 degrees C) to 50 m/s (35.5 degrees C), S1: 31.3 to 40, ST: 25 to 33.8, M: 12.5 to 13.8; alpha 2: 40 to 50, alpha 3: 33 to 40. The group conduction velocities showed different temperature dependence apart from SP2 fibres and alpha 2-motoneurons. (6) Upon retrograde bladder filling the urinary bladder stretch (S1) and tension receptor afferent (ST) activity levels were undulating and increased.(ABSTRACT TRUNCATED AT 400 WORDS)