title: Clinical assessment of diaphragm strength by cervical magnetic stimulation of the phrenic nerves.
abstract: BACKGROUND
  Accurate assessment of diaphragm strength can be difficult. Transdiaphragmatic pressure (PDI) measurements during volitional manoeuvres are useful but it may be difficult to ensure maximum patient effort. Magnetic stimulation of the phrenic nerves is easy to perform and the results are reproducible in normal subjects. The purpose of the present study was to evaluate the usefulness of magnetic stimulation of the phrenic nerves in the assessment of diaphragm weakness in patients.
  
  
  METHODS
  Sixty-six patients referred for assessment of respiratory muscle strength and 23 normal subjects were studied. Twitch PDI (TwPDI) following magnetic stimulation of the phrenic nerves and sniffPDI were obtained in all individuals. TWPDI following bilateral electrical stimulation of the phrenic nerves was also obtained in eight patients.
  
  
  RESULTS
  Mean (SD) TwPdi for the normal subjects was 31 (6) cm H2O and 18 (11) cm H2O for the patients. TwPDI and sniffPDI were correlated (r = 0.77). Seven of the 37 patients (19%) with a reduced sniffPDI had a TwPDI within the normal range whereas two of the 32 patients (6%) with a reduced TwPDI had a normal sniffPDI. TwPDI was similar with magnetic and electrical stimulation.
  
  
  CONCLUSIONS
  TwPDI following magnetic stimulation of the phrenic nerves is a clinically useful measurement when assessing diaphragm weakness.
authors.affiliation: Respiratory Muscle Laboratory, National Heart and Lung Institute, Royal Brompton Hospital, London, UK.
authors.forename: C H
authors.initials: CH
authors.lastname: Hamnegård
authors.forename: S D
authors.initials: SD
authors.lastname: Wragg
authors.forename: G H
authors.initials: GH
authors.lastname: Mills
authors.forename: D
authors.initials: D
authors.lastname: Kyroussis
authors.forename: M I
authors.initials: MI
authors.lastname: Polkey
authors.forename: B
authors.initials: B
authors.lastname: Bake
authors.forename: J
authors.initials: J
authors.lastname: Moxham
authors.forename: M
authors.initials: M
authors.lastname: Green
mesh_terms: D000328:Adult; D000368:Aged; D003964:Diaphragm / Q000503:physiopathology*; D004558:Electric Stimulation; D005260:Female; D006801:Humans; D008280:Magnetics; D008297:Male; D008875:Middle Aged; D010791:Phrenic Nerve / Q000502:physiology*