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Original article
Neural respiratory drive, pulmonary mechanics and breathlessness in patients with cystic fibrosis
  1. Charles C Reilly1,
  2. Katie Ward1,
  3. Caroline J Jolley1,
  4. Alan C Lunt1,
  5. Joerg Steier1,
  6. Caroline Elston2,
  7. Michael I Polkey3,
  8. Gerrard F Rafferty1,
  9. John Moxham1
  1. 1King's College London, Department of Asthma, Allergy and Respiratory Science, London, UK
  2. 2King's College Hospital, Department of Respiratory Medicine, London, UK
  3. 3National Heart and Lung Institute, Royal Brompton Hospital, London, UK
  1. Correspondence to Charles Reilly, 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{at} and charles.c.k.reilly{at}


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 s (FEV1) 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 (FEV1) (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.

Conclusion sEMGpara%max provides a non-invasive marker of neural drive, which reflects disease severity and exercise-induced breathlessness in CF.

  • Cystic fibrosis
  • exercise
  • respiratory measurement
  • respiratory muscles

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  • Funding CCR is supported by a Medical Research Council (London, UK) PhD studentship.

  • Competing interests None.

  • Ethics approval This study was conducted with the approval of King's College London.

  • Provenance and peer review Not commissioned; externally peer reviewed.