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

Abstract

(1) Humans with spinal cord lesions often show detrusor-sphincteric dyssynergia of the urinary bladder which is reflected urodynamically in the detrusor pressure and a simultaneous increase in electromyographic pelvic floor activity. (2) The time-course of the increase in the secondary muscle spindle afferent activity, induced by the parasympathetic nervous system in muscle spindles contributing to continence, is very similar to that of detrusor pressure. The detrusor-sphincteric dyssynergia is therefore analysed by comparing the natural impulse patterns of secondary muscle spindle afferents (SP2) and sphincteric motoneurons in a brain-dead human with those in patients with spinal cord lesion. The parasympathetic nervous system was activated by painful bladder catheter pulling. (3) In a brain-dead human the sphinteric motoneurons subserving continence were inhibited at a time, when preganglionic parasympathetic efferents increased their activity for 10 s and an SP2 fibre increased its activity for several minutes. In a paraplegic with a strong bladder dysfunction, the SP2 fibre activity increased, due to parasympathetic activation, lasted for approx. 1 min, showed undulations and its amplitude was smaller than that measured in a brain-dead human. The sphincteric motoneurons were not inhibited. (4) In the brain-dead human, an SP2 fibre showed doublet firing with interspike intervals (IIs) of a duration between 10 and 14 ms for low level parasympathetic activation. For high level parasympathetic activation this single parent spindle afferent fibre showed multi-ending regular firing of up to 6 endings with IIs of a duration of predominantly 15 to 25 ms. In one paraplegic with a strong bladder dysfunction the doublet firing was less regular, even though two II peaks at 10.2 and 11.2 ms occurred in a II distribution similar to the brain-dead human. The multi-ending regular firing was replaced by a repeated burst firing. In a second paraplegic with strong detrusor-sphincteric dyssynergia the burst firing consisted of up to 6 impulses with increasing IIs and a first II of approx. 0.2 ms (transmission frequency 5000 Hz). In a third paraplegic with a lesser dysfunction of the bladder a highly activated SP2 fibre showed an activity pattern intermediate to those of multi-ending regular firing and burst firing. (5) The time constant for the activity decrease of a spindle afferent fibre following parasympathetic activation was to 31 s in a paraplegic and approx. 40 s in a brain-dead human. It is concluded that the muscle spindles are unchanged following spinal cord lesion. the pathologic firing patterns of the SP2 fibres are thus a result of neuronal network changes in the parasympathetic nervous system of the sacral micturition center. (6) Differences in axon membrane properties between animals and humans, simultaneous action of the somatic and the parasympathetic divisions, the detrusor-sphincteric coordination, hyperreflexia and clinical implications are discussed.