title: Sensitivity to ischaemia of single sympathetic nerve fibres innervating the dorsum of the human foot.
abstract: Changes in nerve conduction velocity following an impulse (i.e. velocity recovery cycles) reflect after-potentials, and can provide an indication of altered nerve membrane properties. This study used microneurography to assess the effects of ischaemia on single human sympathetic fibres innervating the dorsum of the foot. It was found that velocity recovery cycles can distinguish whether a sympathetic nerve fibre is depolarized or not. The method may be used to detect membrane depolarization of sympathetic nerve fibres in human patients when autonomic neuropathy is suspected.
  
  
  
  The aim of this study was to determine whether velocity recovery cycles (VRCs) could detect the effects of ischaemia on sympathetic nerve fibres. VRCs of human sympathetic nerve fibres of the superficial peroneal nerve innervating the dorsum of the foot were recorded by microneurography in seven healthy volunteers. Sympathetic nerve fibres were identified by studying their response to manoeuvres increasing sympathetic outflow and by measuring activity-dependent slowing at 2 Hz stimulation. VRCs were assessed at rest, during 30 min of induced limb ischaemia and during 20 min of recovery after ischaemia. From each VRC was measured the relative refractory period (RRP), the supernormality and the time to peak supernormality (SN@). During ischaemia, RRP increased from the baseline value of 37.4 ± 8.7 ms (mean ± SEM) to 67.1 ± 12.1 ms (P < 0.01) and SN@ increased from 68.6 ± 9.8 ms to 133.8 ± 11.0 ms (P < 0.005). The difference between SN@ and RRP separated ischaemic from non-ischaemic sympathetic nerve fibres. It is concluded that these sympathetic nerve fibres are sensitive to ischaemia, and that VRCs provide a method to study changes of axonal membrane potential of human sympathetic nerve fibres in vivo.
authors.affiliation: Department of Neurosurgery, Inselspital, Bern University Hospital and University of Bern, Bern, Switzerland.|Department of Neurology, Inselspital, Bern University Hospital and University of Bern, Bern, Switzerland.
authors.forename: W J
authors.initials: WJ
authors.lastname: Z'Graggen
authors.affiliation: Neuroscience Technologies, Barcelona, Spain.
authors.forename: R
authors.identifier: 0000-0002-3803-6522
authors.initials: R
authors.lastname: Solà
authors.affiliation: Department of Neurology, Inselspital, Bern University Hospital and University of Bern, Bern, Switzerland.
authors.forename: N E
authors.initials: NE
authors.lastname: Graf
authors.affiliation: Neuroscience Technologies, Barcelona, Spain.
authors.forename: J
authors.initials: J
authors.lastname: Serra
authors.affiliation: Sobell Department of Motor Neuroscience and Movement Disorders, Institute of Neurology, University College London, London, UK.
authors.forename: H
authors.identifier: 0000-0003-1097-731X
authors.initials: H
authors.lastname: Bostock
mesh_terms: D000200:Action Potentials; D000328:Adult; D005260:Female; D005528:Foot / Q000098:blood supply / Q000294:innervation*; D006801:Humans; D007511:Ischemia / Q000503:physiopathology*; D019194:Ischemic Preconditioning / Q000009:adverse effects; D008297:Male; D018482:Muscle, Skeletal / Q000098:blood supply / Q000294:innervation; D012032:Refractory Period, Electrophysiological; D012039:Regional Blood Flow; D013564:Sympathetic Nervous System / Q000502:physiology*
keywords: ischaemia; supernormality; sympathetic nerve fibre