Peak oxygen uptake and breathing pattern in COPD patients--a four-year longitudinal study.
BACKGROUND
Activities of daily living in patients with chronic obstructive pulmonary disease (COPD) are limited by exertional dyspnea and reduced exercise capacity. The aims of the study were to examine longitudinal changes in peak oxygen uptake (V̇O2peak), peak minute ventilation (V̇Epeak) and breathing pattern over four years in a group of COPD patients, and to examine potential explanatory variables of change.


METHODS
This longitudinal study included 63 COPD patients, aged 44-75 years, with a mean forced expiratory volume in one second (FEV1) at baseline of 51 % of predicted (SD = 14). The patients performed two cardiopulmonary exercise tests (CPETs) on treadmill 4.5 years apart. The relationship between changes in V̇O2peak and V̇Epeak and possible explanatory variables, including dynamic lung volumes and inspiratory capacity (IC), were analysed by multivariate linear regression analysis. The breathing pattern in terms of the relationship between minute ventilation (V̇E) and tidal volume (VT) was described by a quadratic equation, VT = a + b∙V̇E + c∙V̇E (2), for each test. The VTmax was calculated from the individual quadratic relationships, and was the point where the first derivative of the quadratic equation was zero. The mean changes in the curve parameters (CPET2 minus CPET1) and VTmax were analysed by bivariate and multivariate linear regression analyses with age, sex, height, changes in weight, lung function, IC and inspiratory reserve volume as possible explanatory variables.


RESULTS
Significant reductions in V̇O2peak (p < 0.001) and V̇Epeak (p < 0.001) were related to a decrease in resting IC and in FEV1. Persistent smoking contributed to the reduction in V̇O2peak. The breathing pattern changed towards a lower VT at a given V̇E and was related to the reduction in FEV1.


CONCLUSIONS
Increasing static hyperinflation and increasing airway obstruction were related to a reduction in exercise capacity. The breathing pattern changed towards more shallow breathing, and was related to increasing airway obstruction.
Centre for Evidence-Based Practice, Bergen University College, Bergen, Norway. bente.frisk@hib.no.|Department of Clinical Science, University of Bergen, Bergen, Norway. bente.frisk@hib.no.
Bente
B
Frisk
Department of Clinical Science, University of Bergen, Bergen, Norway. jon.hardie@uib.no.
Jon A
JA
Hardie
Centre for Evidence-Based Practice, Bergen University College, Bergen, Norway. birgitte.espehaug@hib.no.
Birgitte
B
Espehaug
Department of Global Public Health and Primary Care, University of Bergen, Bergen, Norway. liv.strand@uib.no.|Department of Physiotherapy, Haukeland University Hospital, Bergen, Norway. liv.strand@uib.no.
Liv I
LI
Strand
Department of Global Public Health and Primary Care, University of Bergen, Bergen, Norway. rolf.moe-nilssen@uib.no.
Rolf
R
Moe-Nilssen
Department of Clinical Science, University of Bergen, Bergen, Norway. tomas.eagan@uib.no.|Department of Thoracic Medicine, Haukeland University Hospital, Bergen, Norway. tomas.eagan@uib.no.
Tomas M L
TM
Eagan
Department of Clinical Science, University of Bergen, Bergen, Norway. per.bakke@uib.no.
Per S
PS
Bakke
Department of Clinical Science, University of Bergen, Bergen, Norway. einar.thorsen@helse-bergen.no.|Department of Occupational Medicine, Haukeland University Hospital, Bergen, Norway. einar.thorsen@helse-bergen.no.
Einar
E
Thorsen
D000203:Activities of Daily Living; D000328:Adult; D000368:Aged; D018450:Disease Progression; D015444:Exercise / Q000502:physiology*; D005081:Exercise Therapy / Q000379:methods*; D005260:Female; D005500:Follow-Up Studies; D005541:Forced Expiratory Volume; D006801:Humans; D007320:Inspiratory Capacity / Q000502:physiology*; D008297:Male; D008875:Middle Aged; D010100:Oxygen / Q000378:metabolism*; D010101:Oxygen Consumption / Q000502:physiology*; D029424:Pulmonary Disease, Chronic Obstructive / Q000378:metabolism* / Q000503:physiopathology / Q000534:rehabilitation; D013997:Time Factors
D010100:Oxygen