title: Airway obstruction, dynamic hyperinflation, and breathing pattern during incremental exercise in COPD patients.
abstract: Ventilatory capacity is reduced in chronic obstructive pulmonary disease (COPD) patients. Tidal volume (V T) is lower and breathing frequency higher at a given ventilation (V E) compared to healthy subjects. We examined whether airflow limitation and dynamic hyperinflation in COPD patients were related to breathing pattern. An incremental treadmill exercise test was performed in 63 COPD patients (35 men), aged 65 years (48-79 years) with a mean forced expiratory volume in 1 sec (FEV1) of 48% of predicted (SD = 15%). Data were averaged over 20-sec intervals. The relationship between V E and V T was described by the quadratic equation V T = a + bV E + cV E (2) for each subject. The relationships between the curve parameters b and c, and spirometric variables and dynamic hyperinflation measured as the difference in inspiratory capacity from start to end of exercise, were analyzed by multivariate linear regression. The relationship between V E and V T could be described by a quadratic model in 59 patients with median R (2) of 0.90 (0.40-0.98). The linear coefficient (b) was negatively (P = 0.001) and the quadratic coefficient (c) positively (P < 0.001) related to FEV1. Forced vital capacity, gender, height, weight, age, inspiratory reserve volume, and dynamic hyperinflation were not associated with the curve parameters after adjusting for FEV1. We concluded that a quadratic model could satisfactorily describe the relationship between V E and V T in most COPD patients. The curve parameters were related to FEV1. With a lower FEV1, maximal V T was lower and achieved at a lower V E. Dynamic hyperinflation was not related to breathing pattern when adjusting for FEV1.
authors.affiliation: Centre for Evidence-Based Practice, Bergen University College, Bergen, Norway ; Department of Clinical Science, University of Bergen, Bergen, Norway.
authors.forename: Bente
authors.initials: B
authors.lastname: Frisk
authors.affiliation: Centre for Evidence-Based Practice, Bergen University College, Bergen, Norway.
authors.forename: Birgitte
authors.initials: B
authors.lastname: Espehaug
authors.affiliation: Department of Clinical Science, University of Bergen, Bergen, Norway.
authors.forename: Jon A
authors.initials: JA
authors.lastname: Hardie
authors.affiliation: Department of Global Public Health and Primary Care, University of Bergen, Bergen, Norway ; Department of Physiotherapy, Haukeland University Hospital, Bergen, Norway.
authors.forename: Liv I
authors.initials: LI
authors.lastname: Strand
authors.affiliation: Department of Global Public Health and Primary Care, University of Bergen, Bergen, Norway.
authors.forename: Rolf
authors.initials: R
authors.lastname: Moe-Nilssen
authors.affiliation: Department of Clinical Science, University of Bergen, Bergen, Norway ; Department of Thoracic Medicine, Haukeland University Hospital, Bergen, Norway.
authors.forename: Tomas M L
authors.initials: TM
authors.lastname: Eagan
authors.affiliation: Department of Clinical Science, University of Bergen, Bergen, Norway ; Department of Thoracic Medicine, Haukeland University Hospital, Bergen, Norway.
authors.forename: Per S
authors.initials: PS
authors.lastname: Bakke
authors.affiliation: Department of Clinical Science, University of Bergen, Bergen, Norway ; Department of Occupational Medicine, Haukeland University Hospital, Bergen, Norway.
authors.forename: Einar
authors.initials: E
authors.lastname: Thorsen
keywords: Chronic obstructive pulmonary disease; exercise; inspiratory capacity; spirometry
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