title: Assessment of fitness in patients with cystic fibrosis and mild lung disease.
abstract: BACKGROUND
  Maximal exercise testing is used in patients with cystic fibrosis to assess functional status and prognosis. The lactate threshold is an index of aerobic fitness with significant advantages over maximal exercise tests. This study was undertaken to determine if the lactate threshold might be identified, non-invasively, in adult patients with cystic fibrosis and mild lung disease by measurement of ventilatory and gas exchange parameters.
  
  
  METHODS
  Ten subjects with mild cystic fibrosis (forced vital capacity (FVC) > 70% predicted) and 10 healthy controls undertook an incremental exercise test on a bicycle ergometer. Ventilation and gas exchange parameters were measured continually and arterialised venous blood pH, carbon dioxide tension (PCO2), and lactate concentrations were measured at intervals throughout the tests.
  
  
  RESULTS
  In subjects with cystic fibrosis there was no significant difference between the mean gas exchange and lactate thresholds (mean difference 1.0 (95% confidence interval (CI) of the mean -1.5 to 3.44) ml/kg/min). In contrast, there was a significant difference between the mean ventilatory and lactate thresholds (3.8 (95% CI 0.9 to 6.7) ml/kg/min). Arterialised venous PCO2 increased significantly during the exercise tests. In healthy subjects the mean differences between these thresholds were not significantly different from zero and PCO2 fell significantly during the tests.
  
  
  CONCLUSIONS
  The ventilatory threshold significantly overestimates the lactate threshold in subjects with cystic fibrosis induced lung disease because of impaired carbon dioxide excretion during exercise. However, the gas exchange threshold may be used to determine the lactate threshold in this patient group.
authors.affiliation: Department of Physiology, University College, Dublin, Ireland.
authors.forename: P
authors.initials: P
authors.lastname: McLoughlin
authors.forename: D
authors.initials: D
authors.lastname: McKeogh
authors.forename: P
authors.initials: P
authors.lastname: Byrne
authors.forename: G
authors.initials: G
authors.lastname: Finlay
authors.forename: J
authors.initials: J
authors.lastname: Hayes
authors.forename: M X
authors.initials: MX
authors.lastname: FitzGerald
mesh_terms: D000328:Adult; D000704:Analysis of Variance; D003550:Cystic Fibrosis / Q000097:blood / Q000503:physiopathology*; D006801:Humans; D019344:Lactic Acid / Q000097:blood*; D008171:Lung Diseases / Q000097:blood / Q000503:physiopathology; D008297:Male; D010809:Physical Fitness; D011659:Pulmonary Gas Exchange
chemical_list: D019344:Lactic Acid