title: Neural respiratory drive, pulmonary mechanics and breathlessness in patients with cystic fibrosis.
abstract: BACKGROUND
  Neural respiratory drive (NRD) measured from the diaphragm electromyogram (EMGdi) reflects the load/capacity balance of the respiratory muscle pump and is a marker of lung disease severity. EMGdi measurement is invasive, but recording the EMG from the parasternal intercostal muscles using surface electrodes (sEMGpara) could provide a non-invasive method of assessing NRD and disease severity. Objectives To test the hypothesis that NRD measured by sEMGpara correlates with EMGdi, to provide an index of disease severity in cystic fibrosis (CF) and to relate to exercise-induced breathlessness.
  
  
  METHODS
  15 patients with CF (mean forced expiratory volume in 1&emsp14;s (FEV(1)) 53.5% predicted) and 15 age-matched healthy controls were studied. sEMGpara and EMGdi were recorded at rest and during exercise. sEMGpara was recorded using surface electrodes and EMGdi using a multipair oesophageal electrode catheter. Signals were normalised using the peak EMG recorded during maximum respiratory manoeuvres and expressed as EMG%max. The respiratory pattern, metabolic data, oesophageal and gastric pressures and Borg scores were also recorded.
  
  
  RESULTS
  Mean (SD) resting sEMGpara%max and EMGdi%max were higher in patients with CF than in controls (13.1 (7)% and 18.5 (7.5)% vs 5.8 (3)% and 7.5 (2)%, respectively, p<0.001). In the patients with CF, resting sEMGpara%max and EMGdi%max were related to the degree of airways obstruction (FEV(1)) (r = -0.91 and r = -0.82, both p<0.001), hyperinflation (r = 0.63 and r = 0.56, both p<0.001) and dynamic lung compliance (r = -0.53 and r = -0.59, both p<0.001). During exercise, sEMGpara%max and EMGdi%max were strongly correlated with breathlessness in the patients with CF before (r = 0.906, p<0.001) and after (r = 0.975, p<0.001) the onset of neuromechanical dissociation.
  
  
  CONCLUSIONS
  sEMGpara%max provides a non-invasive marker of neural drive, which reflects disease severity and exercise-induced breathlessness in CF.
authors.affiliation: Department of Asthma, Allergy and Respiratory Science, King's College London School of Medicine, King's College Hospital, Bessemer Road, London SE5 9PJ, UK. charles.c.reilly@kcl.ac.uk
authors.forename: Charles C
authors.initials: CC
authors.lastname: Reilly
authors.forename: Katie
authors.initials: K
authors.lastname: Ward
authors.forename: Caroline J
authors.initials: CJ
authors.lastname: Jolley
authors.forename: Alan C
authors.initials: AC
authors.lastname: Lunt
authors.forename: Joerg
authors.initials: J
authors.lastname: Steier
authors.forename: Caroline
authors.initials: C
authors.lastname: Elston
authors.forename: Michael I
authors.initials: MI
authors.lastname: Polkey
authors.forename: Gerrard F
authors.initials: GF
authors.lastname: Rafferty
authors.forename: John
authors.initials: J
authors.lastname: Moxham
mesh_terms: D000293:Adolescent; D000328:Adult; D003550:Cystic Fibrosis / Q000150:complications* / Q000503:physiopathology*; D003964:Diaphragm / Q000503:physiopathology; D004417:Dyspnea / Q000209:etiology* / Q000503:physiopathology; D004576:Electromyography / Q000379:methods; D015444:Exercise / Q000502:physiology; D005080:Exercise Test / Q000379:methods; D005260:Female; D005541:Forced Expiratory Volume / Q000502:physiology; D006801:Humans; D007366:Intercostal Muscles / Q000503:physiopathology; D008297:Male; D015203:Reproducibility of Results; D015656:Respiratory Mechanics / Q000502:physiology*; D012720:Severity of Illness Index; D014797:Vital Capacity / Q000502:physiology; D055815:Young Adult