title: Ventilation Distribution Heterogeneity at Rest as a Marker of Exercise Impairment in Mild-to-Advanced COPD.
abstract: The difference between total lung capacity (TLC) by body plethysmography and alveolar volume (VA) from the single-breath lung diffusing capacity measurement provides an index of ventilation distribution inequalities in COPD. The relevance of these abnormalities to dyspnea and exercise intolerance across the continuum of disease severity remains unknown. Two-hundred and seventy-six COPD patients distributed across GOLD grades 1 to 4 and 67 healthy controls were evaluated. The "poorly communicating fraction" (PCF) of the TLC was estimated as the ratio (%) of TLC to VA. Healthy subjects showed significantly lower PCF values compared to GOLD grades 1 to 4 (10 ± 3% vs. 17 ± 8% vs. 27 ± 10% vs. 37 ± 10% vs. 56 ± 11%, respectively; p < 0.05). Pulmonary gas exchange impairment, mechanical ventilatory constraints and ventilation-corrected dyspnea scores worsened across PCF tertiles (p < 0.05). Of note, GOLD grades 1 and 2 patients with the highest PCF values had pronounced exercise ventilatory inefficiency and dyspnea as a limiting symptom. In fact, dyspnea was a significant contributor to exercise limitation only in those with "moderate" or "extensive" PCF (p < 0.05). A receiver operating characteristics curve analysis revealed that PCF was a better predictor of severely reduced maximal exercise capacity than traditional pulmonary function indexes including FEV1 (area under the curve (95% confidence interval) = 0.85 (0.81-0.89), best cutoff = 33.4%; p < 0.01). In conclusion, PCF is a readily available functional marker of gas exchange and mechanical abnormalities relevant to dyspnea and exercise intolerance across the COPD grades.
authors.affiliation: 1 Respiratory Investigation Unit, Queen's University & Kingston General Hospital , Kingston, Ontario , Canada.
authors.forename: J Alberto
authors.initials: JA
authors.lastname: Neder
authors.forename: Conor D J
authors.initials: CD
authors.lastname: O'Donnell
authors.forename: Julia
authors.initials: J
authors.lastname: Cory
authors.forename: Daniel
authors.initials: D
authors.lastname: Langer
authors.forename: Casey E
authors.initials: CE
authors.lastname: Ciavaglia
authors.forename: Y
authors.initials: Y
authors.lastname: Ling
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; D016022:Case-Control Studies; D004417:Dyspnea / Q000503:physiopathology; D017079:Exercise Tolerance / Q000502:physiology*; D005260:Female; D006801:Humans; D008297:Male; D011653:Pulmonary Diffusing Capacity / Q000502:physiology*; D029424:Pulmonary Disease, Chronic Obstructive / Q000503:physiopathology*; D011659:Pulmonary Gas Exchange / Q000502:physiology; D012372:ROC Curve; D012146:Rest / Q000502:physiology*; D012189:Retrospective Studies; D012720:Severity of Illness Index; D014109:Total Lung Capacity / Q000502:physiology*
keywords: breathlessness; exertion; lung mechanics; pulmonary function tests