title: Physiological markers of exercise capacity and lung disease severity in cystic fibrosis.
abstract: Peak aerobic capacity (VO2peak) is an important outcome measure in cystic fibrosis (CF), but measurement is not widely available and can be influenced by patient motivation, pain and fatigue. Alternative markers of disease severity would be helpful. Neural respiratory drive, measured using parasternal intercostal muscle electromyography (EMGpara), reflects the load to capacity balance of the respiratory system and provides a composite measure of pulmonary function impairment in CF. The aim of the study was to investigate the relationship between exercise capacity, EMGpara and established measures of pulmonary function in clinically stable adult CF patients.
  
  
  
  Twenty CF patients (12 males, median (range) age: 22.3 (17.0-43.1) years) performed the 10-m incremental shuttle walk test (ISWT) maximally with contemporaneous measures of aerobic metabolism. EMGpara was recorded from second intercostal space at rest and normalized using peak electromyogram activity obtained during maximum respiratory manoeuvres and expressed as EMGpara%max (EMGpara expressed as a percentage of maximum).
  
  
  
  VO2peak was strongly correlated with ISWT distance (r = 0.864, P < 0.0001). Lung gas transfer (TLCO) % predicted was best correlated with VO2peak (r = 0.842, P < 0.0001) and ISWT distance (r = 0.788, P < 0.0001). EMGpara%max also correlated with VO2peak (-0.757, P < 0.0001), while the relationships between exercise outcome measures and forced expiratory volume in 1 s (FEV1) % predicted and forced vital capacity (FVC) % predicted were less strong. A TLCO% predicted of <70.5% was the strongest predictor of VO2peak <32 mL/min/kg (area under the curve (AUC): 0.96, 100% sensitivity, 83.3% specificity). ISWT distance and EMGpara%max also performed well, with other pulmonary function variables demonstrating poorer predictive ability.
  
  
  
  TLCO% predicted and EMGpara%max relate strongly to exercise performance markers in CF and may provide alternative predictors of lung disease progression.
authors.affiliation: Division of Asthma, Allergy and Lung Biology, Department of Respiratory Medicine (Chest Unit), King's College London, London, UK.
authors.forename: Laurie
authors.initials: L
authors.lastname: Smith
authors.affiliation: Division of Asthma, Allergy and Lung Biology, Department of Respiratory Medicine (Chest Unit), King's College London, London, UK.|King's College Hospital NHS Foundation Trust, London, UK.
authors.forename: Charles C
authors.initials: CC
authors.lastname: Reilly
authors.affiliation: Division of Asthma, Allergy and Lung Biology, Department of Respiratory Medicine (Chest Unit), King's College London, London, UK.
authors.forename: Victoria
authors.initials: V
authors.lastname: MacBean
authors.affiliation: Division of Asthma, Allergy and Lung Biology, Department of Respiratory Medicine (Chest Unit), King's College London, London, UK.|Centre for Human and Aerospace Physiological Sciences, King's College London, London, UK.
authors.forename: Caroline J
authors.initials: CJ
authors.lastname: Jolley
authors.affiliation: King's College Hospital NHS Foundation Trust, London, UK.
authors.forename: Caroline
authors.initials: C
authors.lastname: Elston
authors.affiliation: Division of Asthma, Allergy and Lung Biology, Department of Respiratory Medicine (Chest Unit), King's College London, London, UK.
authors.forename: John
authors.initials: J
authors.lastname: Moxham
authors.affiliation: Division of Asthma, Allergy and Lung Biology, Department of Respiratory Medicine (Chest Unit), King's College London, London, UK.
authors.forename: Gerrard F
authors.identifier: 0000-0001-9520-6500
authors.initials: GF
authors.lastname: Rafferty
mesh_terms: D000293:Adolescent; D000328:Adult; D015415:Biomarkers; D003550:Cystic Fibrosis / Q000150:complications* / Q000503:physiopathology; D018450:Disease Progression; D004576:Electromyography / Q000379:methods*; D005080:Exercise Test; D017079:Exercise Tolerance / Q000502:physiology*; D005260:Female; D005541:Forced Expiratory Volume; D006801:Humans; D007366:Intercostal Muscles / Q000503:physiopathology; D008171:Lung Diseases / Q000150:complications / Q000175:diagnosis*; D008297:Male; D008875:Middle Aged; D012680:Sensitivity and Specificity; D012720:Severity of Illness Index; D000070857:Walk Test
chemical_list: D015415:Biomarkers
keywords: cystic fibrosis; electromyography; exercise; intercostal muscles; respiratory function