title: Emphysema on Thoracic CT and Exercise Ventilatory Inefficiency in Mild-to-Moderate COPD.
abstract: There is growing evidence that emphysema on thoracic computed tomography (CT) is associated with poor exercise tolerance in COPD patients with only mild-to-moderate airflow obstruction. We hypothesized that an excessive ventilatory response to exercise (ventilatory inefficiency) would underlie these abnormalities. In a prospective study, 19 patients (FEV1= 82 ± 13%, 12 Global Initiative for Chronic Obstructive Lung Disease (GOLD) stage 1) and 26 controls underwent an incremental exercise test. Ventilatory inefficiency was assessed by the ventilation ([Formula: see text]E)/CO2output ([Formula: see text]CO2) nadir. Pulmonary blood flow (PBF) in a submaximal test was calculated by inert gas rebreathing. Emphysema was quantified as % of attenuation areas below 950 HU. Patients typically presented with centrilobular emphysema (76.8 ± 10.1% of total emphysema) in the upper lobes (upper/total lung ratio = 0.82 ± 0.04). They had lower peak oxygen uptake ([Formula: see text]O2), higher [Formula: see text]E/[Formula: see text]CO2nadir, and greater dyspnea scores than controls (p < 0.05). Lower peak [Formula: see text]O2and worse dyspnea were found in patients with higher [Formula: see text]E/[Formula: see text]CO2nadirs (≥30). Patients had blunted increases in PBF from rest to iso-[Formula: see text]O2exercise (p < 0.05). Higher [Formula: see text]E/[Formula: see text]CO2nadir in COPD was associated with emphysema severity (r = 0.63) which, in turn, was related to reduced lung diffusing capacity (r = -0.72) and blunted changes in PBF from rest to exercise (r = -0.69) (p < 0.01). Ventilation "wasted" in emphysematous areas is associated with impaired exercise ventilatory efficiency in mild-to-moderate COPD. Exercise ventilatory inefficiency links structure (emphysema) and function (DLCO) to a key clinical outcome (poor exercise tolerance) in COPD patients with only modest spirometric abnormalities.
authors.affiliation: a Laboratory of Clinical Exercise Physiology (LACEP), Division of Respiratory and Critical Care Medicine, Department of Medicine, Queen's University , Kingston , ON , Canada.
authors.forename: Joshua H
authors.initials: JH
authors.lastname: Jones
authors.affiliation: a Laboratory of Clinical Exercise Physiology (LACEP), Division of Respiratory and Critical Care Medicine, Department of Medicine, Queen's University , Kingston , ON , Canada.
authors.forename: Joel T
authors.initials: JT
authors.lastname: Zelt
authors.affiliation: a Laboratory of Clinical Exercise Physiology (LACEP), Division of Respiratory and Critical Care Medicine, Department of Medicine, Queen's University , Kingston , ON , Canada.
authors.forename: Daniel M
authors.initials: DM
authors.lastname: Hirai
authors.affiliation: a Laboratory of Clinical Exercise Physiology (LACEP), Division of Respiratory and Critical Care Medicine, Department of Medicine, Queen's University , Kingston , ON , Canada.
authors.forename: Camilla V
authors.initials: CV
authors.lastname: Diniz
authors.affiliation: a Laboratory of Clinical Exercise Physiology (LACEP), Division of Respiratory and Critical Care Medicine, Department of Medicine, Queen's University , Kingston , ON , Canada.
authors.forename: Aida
authors.initials: A
authors.lastname: Zaza
authors.affiliation: b Respiratory Investigation Unit (RIU), Division of Respiratory and Critical Care Medicine, Department of Medicine, Queen's University , Kingston , ON , Canada.
authors.forename: Denis E
authors.initials: DE
authors.lastname: O'Donnell
authors.affiliation: a Laboratory of Clinical Exercise Physiology (LACEP), Division of Respiratory and Critical Care Medicine, Department of Medicine, Queen's University , Kingston , ON , Canada.
authors.forename: J Alberto
authors.initials: JA
authors.lastname: Neder
mesh_terms: D000368:Aged; D002245:Carbon Dioxide / Q000378:metabolism; D016022:Case-Control Studies; D004417:Dyspnea / Q000209:etiology; D015444:Exercise / Q000502:physiology*; D005080:Exercise Test; D017079:Exercise Tolerance; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D010101:Oxygen Consumption; D011446:Prospective Studies; D011652:Pulmonary Circulation; D029424:Pulmonary Disease, Chronic Obstructive / Q000150:complications / Q000503:physiopathology*; D011656:Pulmonary Emphysema / Q000150:complications / Q000000981:diagnostic imaging* / Q000503:physiopathology*; D011659:Pulmonary Gas Exchange; D012123:Pulmonary Ventilation; D013902:Radiography, Thoracic; D012720:Severity of Illness Index; D014057:Tomography, X-Ray Computed
chemical_list: D002245:Carbon Dioxide
keywords: Cardiopulmonary exercise testing; computed tomography; dyspnea; emphysema; gas exchange; ventilation