title: Does the respiratory system limit exercise in mild chronic obstructive pulmonary disease?
abstract: BACKGROUND
  It is not known if abnormal dynamic respiratory mechanics actually limit exercise in patients with mild chronic obstructive pulmonary disease (COPD). We reasoned that failure to increase peak ventilation and Vt in response to dead space (DS) loading during exercise would indicate true ventilatory limitation to exercise in mild COPD.
  
  
  OBJECTIVE
  To compare the effects of DS loading during exercise on ventilation, breathing pattern, operating lung volumes, and dyspnea intensity in subjects with mild symptomatic COPD and age- and sex-matched healthy control subjects.
  
  
  METHODS
  Twenty subjects with Global Initiative for Chronic Obstructive Lung Disease stage I COPD and 20 healthy subjects completed two symptom-limited incremental cycle exercise tests, in randomized order: unloaded control and added DS of 0.6 L.
  
  
  RESULTS
  Peak oxygen uptake and ventilation were significantly lower in COPD than in health by 36% and 41%, respectively. With added DS compared with control, both groups had small decreases in peak work rate and no significant increase in peak ventilation. In health, peak Vt and end-inspiratory lung volume increased significantly with DS. In contrast, the COPD group failed to increase peak end-inspiratory lung volume and had a significantly smaller increase in peak Vt during DS. At 60 W, a 50% smaller increase in Vt (P < 0.001) in response to added DS in COPD compared with health was associated with a greater increase in dyspnea intensity (P = 0.0005).
  
  
  CONCLUSIONS
  These results show that the respiratory system reached or approached its physiologic limit in mild COPD at a lower peak work rate and ventilation than in healthy participants. Clinical trial registered with www.clinicaltrials.gov (NCT 00975403).
authors.affiliation: Respiratory Investigation Unit, Department of Medicine, Queen's University and Kingston General Hospital, Kingston, Ontario, Canada.
authors.forename: Roberto C
authors.initials: RC
authors.lastname: Chin
authors.forename: Jordan A
authors.initials: JA
authors.lastname: Guenette
authors.forename: Sicheng
authors.initials: S
authors.lastname: Cheng
authors.forename: Natya
authors.initials: N
authors.lastname: Raghavan
authors.forename: Naparat
authors.initials: N
authors.lastname: Amornputtisathaporn
authors.forename: Arturo
authors.initials: A
authors.lastname: Cortés-Télles
authors.forename: Katherine A
authors.initials: KA
authors.lastname: Webb
authors.forename: Denis E
authors.initials: DE
authors.lastname: O'Donnell
mesh_terms: D000368:Aged; D003430:Cross-Sectional Studies; D015444:Exercise; D005260:Female; D006801:Humans; D008297:Male; D029424:Pulmonary Disease, Chronic Obstructive / Q000503:physiopathology*; D012126:Respiratory Dead Space