title: Respiratory factors do not limit maximal symptom-limited exercise in patients with mild cystic fibrosis lung disease.
abstract: To evaluate whether respiratory factors limit exercise capacity in patients with mild cystic fibrosis (CF) lung disease (mean FEV(1) = 76 +/- 7.7% predicted) we stressed the respiratory system of seven patients using added dead space (V(D)). Primary outcomes were exercise duration (Ex(dur)) and maximal oxygen uptake (VO(2max)). Dyspnoea/leg-discomfort were assessed at end-exercise. Ex(dur) was identical between control and V(D) studies (520 +/- 152 versus 511 +/ -166 s, p = NS) as was VO(2max)(1.6 +/- 0.5 versus 1.6 +/- 0.6 L/min, p = NS). Significant resting, sub-maximal and maximal workload increases in minute ventilation (V(E)) were detected (70.8 +/- 13.7 versus 79.5 +/- 16.9 L/min, p < 0.05). Analysis of breathing pattern revealed increases in V(E) were attributable to increases in tidal volume (2.0 +/- 0.5 versus 2.2 +/- 0.6 L, p < 0.05) with no change in respiratory frequency. There was no difference in dyspnoea/leg discomfort between tests. The increase in V(E) in response to V(D), with no change in [Exdur/VO(2max) suggests maximal symptom-limited exercise limitation is not primarily limited by respiratory factors in mild CF lung disease. Focused investigation and treatment of non-respiratory factors contributing to exercise limitation may improve exercise rehabilitation in this patient group.
authors.affiliation: Department of Respiratory Medicine and National Referral Centre for Adult Cystic Fibrosis, St. Vincent's University Hospital, Dublin, Ireland. jdodd@iolfree.ie
authors.forename: Jonathan D
authors.initials: JD
authors.lastname: Dodd
authors.forename: Sinead C
authors.initials: SC
authors.lastname: Barry
authors.forename: Charles G
authors.initials: CG
authors.lastname: Gallagher
mesh_terms: D000328:Adult; D003550:Cystic Fibrosis / Q000150:complications*; D015444:Exercise / Q000502:physiology*; D005080:Exercise Test / Q000379:methods; D017079:Exercise Tolerance / Q000502:physiology*; D005260:Female; D006801:Humans; D008171:Lung Diseases / Q000209:etiology* / Q000503:physiopathology*; D008176:Lung Volume Measurements / Q000379:methods; D008297:Male; D008451:Maximal Voluntary Ventilation / Q000502:physiology; D012119:Respiration; D012126:Respiratory Dead Space / Q000502:physiology; D012129:Respiratory Function Tests / Q000379:methods; D015656:Respiratory Mechanics / Q000502:physiology; D013997:Time Factors