Usefulness of phrenic nerve stimulation to measure upper airway collapsibility in normal awake subjects.
Upper airway (UA) collapsibility can be characterized during sleep by looking at the changes in inspiratory flow limitation (IFL) with changing nasal pressure. IFL can be induced during wakefulness using phrenic nerve stimulation (PNS) applied during exclusive nasal breathing. The aim of the study was to evaluate the possibility of measuring UA critical pressure (Pcrit) in normal awaked subjects using electrical PNS (EPNS) or bilateral anterior magnetic phrenic stimulation (BAMPS). Instantaneous flow, esophageal (Peso) and mask pressures (Pmask), and genioglossal (GG) end-expiratory EMG activity were recorded in 13 normal subjects (4F, 9M) with randomly changing Pmask (0 to -20 cmH2O). For each trial, we examined the relationship between maximal inspiratory flow (Vtmax) of IFL twitches and the corresponding Pmask. Pcrit could be determined in 12 subjects (mean -33.5 +/- 16.3 cmH2O). No difference in Pcrit values was found between the EPNS and BAMPS methods but the strength of the Vtmax/Pmask relationship was higher with BAMPS. GG end-expiratory EMG activity increased with decreasing Pmask but no significant relationship was found between the slope of the GG end-expiratory EMG activity/Pmask relationship and Pcrit. We conclude that: (1) Pcrit can be measured during wakefulness in normal using PNS: (2) Pcrit measurements may be easier and more reliable with BAMPS than EPNS: and (3) Pcrit does not seem to be influenced by the pressure-related changes in GG end-expiratory EMG.
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Centre de Recherche, Hôpital Laval, Institut Universitaire de Cardiologie et de Pneumologie de l'Université Laval, 2725 Chemin Sainte-Foy, Sainte-Foy, Quebec, Canada GW 4G5.
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D000328:Adult; D004558:Electric Stimulation / Q000379:methods; D004576:Electromyography / Q000379:methods / Q000706:statistics & numerical data; D005260:Female; D006801:Humans; D007320:Inspiratory Capacity / Q000502:physiology; D016018:Least-Squares Analysis; D008280:Magnetics; D008297:Male; D008875:Middle Aged; D010791:Phrenic Nerve / Q000502:physiology*; D012119:Respiration; D014851:Wakefulness / Q000502:physiology*