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Physiological markers of exercise capacity and lung disease severity in cystic fibrosis
Author(s) -
Smith Laurie,
Reilly Charles C.,
MacBean Victoria,
Jolley Caroline J.,
Elston Caroline,
Moxham John,
Rafferty Gerrard F.
Publication year - 2017
Publication title -
respirology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.857
H-Index - 85
eISSN - 1440-1843
pISSN - 1323-7799
DOI - 10.1111/resp.12954
Subject(s) - medicine , parasternal line , vital capacity , lung volumes , pulmonary function testing , cystic fibrosis , cardiology , vo2 max , aerobic capacity , respiratory system , lung , physical therapy , lung function , diffusing capacity , heart rate , blood pressure
Background and objective Peak aerobic capacity ( VO 2 peak ) 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. Methods 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). Results VO 2 peak was strongly correlated with ISWT distance (r = 0.864, P < 0.0001). Lung gas transfer ( T L CO ) % predicted was best correlated with VO 2 peak (r = 0.842, P < 0.0001) and ISWT distance (r = 0.788, P < 0.0001). EMGpara %max also correlated with VO 2 peak (−0.757, P < 0.0001), while the relationships between exercise outcome measures and forced expiratory volume in 1 s ( FEV 1 ) % predicted and forced vital capacity ( FVC ) % predicted were less strong. A T L CO % predicted of <70.5% was the strongest predictor of VO 2 peak <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. Conclusion T L CO % predicted and EMGpara %max relate strongly to exercise performance markers in CF and may provide alternative predictors of lung disease progression.