title: Diaphragmatic fatigue during inspiratory muscle loading in normoxia and hypoxia.
abstract: BACKGROUND
  Diaphragmatic fatigue (DF) occurs during strenuous loading of respiratory muscles (e.g., heavy-intensity whole-body exercise, normocapnic hyperpnea, inspiratory resistive breathing). DF develops early on during normoxia, without further decline toward task failure; however, its progression during inspiratory muscle loading in during hypoxia remains unclear. Therefore, the present study used volume-corrected transdiaphragmatic pressures during supramaximal magnetic phrenic nerve stimulation (Pdi,twc) to investigate the effect of hypoxia on the progression of diaphragmatic fatigue during inspiratory muscle loading.
  
  
  METHODS
  Seventeen subjects completed two standardized rounds of inspiratory muscle loading (blinded, randomized) under the following conditions: (i) normoxia, and (ii) normobaric hypoxia (SpO2 80%), with Pdi,twc assessment every 45 s.
  
  
  RESULTS
  In fatiguers (i.e., Pdi,twc reduction >10%, n=10), biometric approximation during normoxia is best represented by Pdi,twc=4.06+0.83 exp(-0.19 × x), in contrast to Pdi,twc=4.38-(0.05 × x) during hypoxia.
  
  
  CONCLUSIONS
  Progression of diaphragmatic fatigue during inspiratory muscle loading assessed by Pdi,tw differs between normoxia and normobaric hypoxia: in the former, Pdi,tw follows an exponential decay, whereas during hypoxia, Pdi,tw follows a linear decline.
authors: Department of Pneumology and Intensive Care Medicine, Academic Teaching Hospital Klinikum Konstanz, Germany; Department of Pneumology, University Hospital Freiburg, Germany. Electronic address: david.walker@klinikum-konstanz.de.
authors: David Johannes
authors: DJ
authors: Walker
authors: Department of Pneumology and Intensive Care Medicine, Academic Teaching Hospital Klinikum Konstanz, Germany; Department of Pneumology, University Hospital Freiburg, Germany.
authors: Franziska
authors: F
authors: Farquharson
authors: Department of Pneumology and Intensive Care Medicine, Academic Teaching Hospital Klinikum Konstanz, Germany; Department of Pneumology, University Hospital Freiburg, Germany.
authors: Hannes
authors: H
authors: Klenze
authors: Department of Pneumology and Intensive Care Medicine, Academic Teaching Hospital Klinikum Konstanz, Germany.
authors: Stephan
authors: S
authors: Walterspacher
authors: Department of Pneumology, University Hospital Freiburg, Germany.
authors: Lucia
authors: L
authors: Storz
authors: Department of Cardiology and Angiology I, Heart Center Freiburg University, Germany.
authors: Daniel
authors: D
authors: Duerschmied
authors: Department of Applied Public Health (AGW), Furtwangen University, Germany.
authors: Kai
authors: K
authors: Roecker
authors: Department of Pneumology and Intensive Care Medicine, Academic Teaching Hospital Klinikum Konstanz, Germany.
authors: Hans-Joachim
authors: HJ
authors: Kabitz
mesh_terms: D000328:Adult; D000886:Anthropometry; D003964:Diaphragm / Q000502:physiology* / Q000503:physiopathology*; D005260:Female; D006801:Humans; D000860:Hypoxia / Q000503:physiopathology*; D001239:Inhalation / Q000502:physiology*; D016014:Linear Models; D008176:Lung Volume Measurements; D060526:Magnetic Fields; D008297:Male; D018763:Muscle Fatigue / Q000502:physiology*; D017711:Nonlinear Dynamics; D010791:Phrenic Nerve / Q000502:physiology; D011312:Pressure; D016037:Single-Blind Method
keywords: Diaphragm; Hypoxic effects; Inspiratory muscle loading; Threshold loading; Twitch transdiaphragmatic pressure