title: Decline of resting inspiratory capacity in COPD: the impact on breathing pattern, dyspnea, and ventilatory capacity during exercise.
abstract: BACKGROUND
  To better understand the interrelationships among disease severity, inspiratory capacity (IC), breathing pattern, and dyspnea, we studied responses to symptom-limited cycle exercise in a large cohort with COPD.
  
  
  METHODS
  Analysis was conducted on data from two previously published replicate clinical trials in 427 hyperinflated patients with COPD. Patients were divided into disease severity quartiles based on FEV(1) % predicted. Spirometry, plethysmographic lung volumes, and physiologic and perceptual responses to constant work rate (CWR) cycle exercise at 75% of the peak incremental work rate were compared.
  
  
  RESULTS
  Age, body size, and COPD duration were similar across quartiles. As the FEV(1) quartile worsened (mean, 62%, 49%, 39%, and 27% predicted), functional residual capacity increased (144%, 151%, 164%, and 185% predicted), IC decreased (86%, 81%, 69%, and 60% predicted), and peak incremental cycle work rate decreased (66%, 55%, 50%, and 44% predicted); CWR endurance time was 9.7, 9.3, 8.2, and 7.3 min, respectively. During CWR exercise, as FEV(1) quartile worsened, peak minute ventilation ($$\dot{\mathrm{V}}$$e) and tidal volume (Vt) decreased, whereas an inflection or plateau of the Vt response occurred at a progressively lower $$\dot{\mathrm{V}}$$e (P < .0005), similar percentage of peak $$\dot{\mathrm{V}}$$e (82%-86%), and similar Vt/IC ratio (73%-77%). Dyspnea intensity at this inflection point was also similar across quartiles (3.1-3.7 Borg units) but accelerated steeply to intolerable levels thereafter.
  
  
  CONCLUSIONS
  Progressive reduction of the resting IC with increasing disease severity was associated with the appearance of critical constraints on Vt expansion and a sharp increase in dyspnea to intolerable levels at a progressively lower ventilation during exercise.
authors.affiliation: Respiratory Investigation Unit, Department of Medicine, Queen's University and Kingston General Hospital, Kingston, ON. Electronic address: odonnell@queensu.ca.
authors.forename: Denis E
authors.initials: DE
authors.lastname: O'Donnell
authors.affiliation: Respiratory Investigation Unit, Department of Medicine, Queen's University and Kingston General Hospital, Kingston, ON.
authors.forename: Jordan A
authors.initials: JA
authors.lastname: Guenette
authors.affiliation: Centre de Recherche, Institut Universitaire de cardiologie et de pneumologie de Québec, Université Laval, Québec City, QC, Canada.
authors.forename: François
authors.initials: F
authors.lastname: Maltais
authors.affiliation: Respiratory Investigation Unit, Department of Medicine, Queen's University and Kingston General Hospital, Kingston, ON.
authors.forename: Katherine A
authors.initials: KA
authors.lastname: Webb
mesh_terms: D000368:Aged; D003430:Cross-Sectional Studies; D004417:Dyspnea / Q000503:physiopathology*; D015444:Exercise / Q000502:physiology*; D005080:Exercise Test; D005260:Female; D005541:Forced Expiratory Volume / Q000502:physiology; D006801:Humans; D007320:Inspiratory Capacity / Q000502:physiology; D008168:Lung / Q000503:physiopathology*; D008297:Male; D008875:Middle Aged; D029424:Pulmonary Disease, Chronic Obstructive / Q000503:physiopathology*; D012123:Pulmonary Ventilation / Q000502:physiology*; D016032:Randomized Controlled Trials as Topic; D012129:Respiratory Function Tests; D015656:Respiratory Mechanics / Q000502:physiology*; D012146:Rest / Q000502:physiology*; D012189:Retrospective Studies; D013990:Tidal Volume / Q000502:physiology; D013997:Time Factors