title: Effects of airway occlusion on breathing muscle electromyogram signals, during isoflurane anaesthesia, with and without the effects of fentanyl and hypercapnia.
abstract: BACKGROUND
  Expiratory muscle action is prominent during anaesthesia and can impair lung function. This activity is exaggerated by the use of opioids. Airway pressure during occlusion of expiration would be a valuable measure in the study of expiratory muscle activation. However, this would only be valid if the imposed occlusion did not itself alter muscle activation. This possibility can be checked by directly assessing muscle activity by electromyography; varying arterial carbon dioxide tensions and opioid action should be considered.
  
  
  METHODS
  We studied seven spontaneously breathing patients, anaesthetized with nitrous oxide and isoflurane, in four conditions: during an infusion of fentanyl and after naloxone, breathing normally and with breathing stimulated with CO(2). We compared diaphragm and external oblique abdominal electromyogram (EMG) signals during normal and occluded breaths. We also measured chest wall volume and compared airway occlusion pressure, during inspiration and expiration, with the EMG results.
  
  
  RESULTS
  Inspiratory occlusion increased the duration of inspiration during hypercapnia by 20%, but not the rate of electrical activation of the diaphragm, indicating that occlusion does not cause a reflex increase in diaphragm contraction. In contrast, expiratory occlusion did not affect either the duration of expiration or the electrical activity of the external oblique muscles.
  
  
  CONCLUSIONS
  In these conditions, except for a change in inspiratory duration, respiratory muscle activity is unaffected by airway occlusion. Airway occlusion will permit valid measures of muscle activity in inspiration and expiration and provide simple measurements of respiratory muscle function during anaesthesia.
authors.affiliation: Département d'Anésthesie et Réanimation, Hopital Henri Mondor, 51 Avenue du Marechal de Lattre de Tassigny, 94010 Creteil, France. g.b.drummond@ed.ac.uk
authors.forename: G B
authors.initials: GB
authors.lastname: Drummond
authors.forename: G
authors.initials: G
authors.lastname: Dhonneur
authors.forename: K
authors.initials: K
authors.lastname: Kirov
authors.forename: P
authors.initials: P
authors.lastname: Duvaldestin
mesh_terms: D000009:Abdominal Muscles / Q000187:drug effects / Q000502:physiology; D000328:Adult; D000368:Aged; D000402:Airway Obstruction / Q000503:physiopathology*; D000701:Analgesics, Opioid / Q000494:pharmacology*; D018685:Anesthetics, Inhalation / Q000494:pharmacology*; D002245:Carbon Dioxide / Q000494:pharmacology; D002648:Child; D004576:Electromyography; D005260:Female; D005283:Fentanyl / Q000494:pharmacology*; D006801:Humans; D006935:Hypercapnia / Q000503:physiopathology*; D007530:Isoflurane / Q000494:pharmacology*; D008297:Male; D008875:Middle Aged; D009270:Naloxone / Q000494:pharmacology; D009609:Nitrous Oxide / Q000494:pharmacology; D012132:Respiratory Muscles / Q000503:physiopathology
chemical_list: D000701:Analgesics, Opioid; D018685:Anesthetics, Inhalation; D002245:Carbon Dioxide; D009270:Naloxone; D007530:Isoflurane; D009609:Nitrous Oxide; D005283:Fentanyl