title: Dyspnea-pain counterirritation induced by inspiratory threshold loading: a laser-evoked potentials study.
abstract: BACKGROUND
  experimentally induced dyspnea of the work/effort type inhibits, in a top-down manner, the spinal transmission of nociceptive inputs (dyspnea-pain counterirritation). Previous studies have demonstrated that this inhibition can be assessed by measuring the nociceptive flexion reflex (RIII). However, its clinical application is limited because of the strong discomfort associated with the electrical stimuli required to elicit the RIII reflex.
  
  
  OBJECTIVE
  we examined whether the dyspnea-pain counterirritation phenomenon can be evaluated by measuring the effect of work/effort type dyspnea on the magnitude of laser-evoked brain potentials (LEPs).
  
  
  METHODS
  10 normal male volunteers were studied (age: 19-30 years). LEPs were elicited using a CO(2) laser stimulator delivering 10- to 15-ms stimuli of 6 ± 0.7 W over a 12.5 mm(2) area. The EEG was recorded using nine scalp channels. Non-nociceptive somatosensory-evoked potentials (SEPs) served as control. LEPs and SEPs were recorded before, during, and after 10 min of experimentally induced dyspnea [inspiratory threshold loading (ITL)].
  
  
  RESULTS
  pain caused by the nociceptive laser stimulus was mild. ITL consistently induced dyspnea, mostly of the "excessive effort" type. Amplitude of the N2-P2 wave of LEPs decreased by 37.6 ± 13.8% during ITL and was significantly correlated with the intensity of dyspnea [r = 0.66, CI 95% (0.08-0.92, P = 0.0319)]. In contrast, ITL had no effect on the magnitude of non-nociceptive SEPs.
  
  
  CONCLUSIONS
  experimentally induced dyspnea of the work/effort type reduces the magnitude of LEPs. This reduction correlates with the intensity of dyspnea. The recording of LEPs could constitute a clinically applicable approach to assess the dyspnea-pain counterirritation phenomenon in patients.
authors.affiliation: Université Paris 6, Laboratoire de Physiopathologie Respiratoire, Paris, France.
authors.forename: Guillaume
authors.initials: G
authors.lastname: Bouvier
authors.forename: Louis
authors.initials: L
authors.lastname: Laviolette
authors.forename: Felix
authors.initials: F
authors.lastname: Kindler
authors.forename: Lionel
authors.initials: L
authors.lastname: Naccache
authors.forename: André
authors.initials: A
authors.lastname: Mouraux
authors.forename: Thomas
authors.initials: T
authors.lastname: Similowski
authors.forename: Capucine
authors.initials: C
authors.lastname: Morélot-Panzini
mesh_terms: D000328:Adult; D004417:Dyspnea / Q000150:complications / Q000628:therapy*; D004569:Electroencephalography; D005071:Evoked Potentials / Q000502:physiology*; D005073:Evoked Potentials, Somatosensory / Q000502:physiology; D006801:Humans; D053685:Laser Therapy; D008297:Male; D009413:Nerve Fibers, Myelinated / Q000502:physiology; D036421:Nerve Fibers, Unmyelinated / Q000502:physiology; D010146:Pain / Q000209:etiology; D059408:Pain Management / Q000379:methods*; D010147:Pain Measurement; D005082:Physical Exertion / Q000502:physiology; D015656:Respiratory Mechanics / Q000502:physiology; D012815:Signal Processing, Computer-Assisted; D055815:Young Adult