title: Dyspnea as a noxious sensation: inspiratory threshold loading may trigger diffuse noxious inhibitory controls in humans.
abstract: Dyspnea, a leading respiratory symptom, shares many clinical, physiological, and psychological features with pain. Both activate similar brain areas. The neural mechanisms of dyspnea are less well described than those of pain. The present research tested the hypothesis of common pathways between the two sensations. Six healthy men (age 30-40 yr) were studied. The spinal nociceptive flexion reflex (RIII) was first established in response to electrical sural stimulation. Dyspnea was then induced through inspiratory threshold loading, forcing the subjects to develop 70% of their maximal inspiratory pressure to inhale. This led to progressive inhibition of the RIII reflex that reached 50 +/- 12% during the fifth minute of loading (P < 0.001), was correlated to the intensity of the self-evaluated respiratory discomfort, and had recovered 5 min after removal of the load. The myotatic H-reflex was not inhibited by inspiratory loading, arguing against postsynaptic alpha motoneuron inhibition. Dyspnea, like pain, thus induced counterirritation, possibly indicating a C-fiber stimulation and activation of diffuse noxious inhibitory descending controls known to project onto spinal dorsal horn wide dynamic range neurons. This confirms the noxious nature of certain types of breathlessness, thus opening new physiological and perhaps therapeutic perspectives.
authors.affiliation: Laboratoire de Physiopathologie Respiratoire, Service de Pneumologie et de Réanimation, Groupe Hospitalier Pitié Salpétrière, 47-83 boulevard de l'Hôpital, 75651 Paris Cedex 13, France.
authors.forename: Capucine
authors.initials: C
authors.lastname: Morélot-Panzini
authors.forename: Alexandre
authors.initials: A
authors.lastname: Demoule
authors.forename: Christian
authors.initials: C
authors.lastname: Straus
authors.forename: Marc
authors.initials: M
authors.lastname: Zelter
authors.forename: Jean-Philippe
authors.initials: JP
authors.lastname: Derenne
authors.forename: Jean-Claude
authors.initials: JC
authors.lastname: Willer
authors.forename: Thomas
authors.initials: T
authors.lastname: Similowski
mesh_terms: D000328:Adult; D004417:Dyspnea / Q000503:physiopathology*; D004558:Electric Stimulation; D006181:H-Reflex / Q000502:physiology; D006801:Humans; D008297:Male; D009434:Neural Pathways / Q000503:physiopathology; D009619:Nociceptors / Q000502:physiology; D010146:Pain / Q000503:physiopathology*; D017933:Peripheral Nervous System / Q000503:physiopathology; D010791:Phrenic Nerve / Q000502:physiology; D012018:Reflex / Q000502:physiology; D015656:Respiratory Mechanics / Q000502:physiology