Background: It remains unclear how closely the physical inactivity observed in patients with Chronic Obstructive Pulmonary Disease (COPD) relates to the severity of their airflow limitation. Furthermore, it is unknown whether spirometric variables such as maximal voluntary ventilation (MVV) and inspiratory capacity (IC) reflect the level of physical activity in daily life better than the forced expiratory volume in the first second (FEV(1)), the main spirometric variable used to determine the severity of COPD. The objective of the present study was to investigate the relationship between physical activity in daily life and the severity of COPD assessed by different spirometric variables: MVV, IC and FEV(1).
Methods: Forty patients with COPD (21 men; 68+/-7 years; FEV(1) 41+/-14% predicted) were performed spirometry and assessment of the physical activity level in daily life using an accelerometer (SenseWear Armband).
Results: MVV was significantly correlated to total energy expenditure per day, energy expenditure per day in activities demanding more than 3 metabolic equivalents (METs), number of steps per day and time spent per day in moderate and vigorous activities (0.42<or=r<or=0.52; p<0.01 for all). Correlation of these variables with IC and especially FEV(1) was more modest, borderline or not statistically significant. There was no difference in time spent in vigorous activities among patients classified according to the FEV(1)-based GOLD stages II, III and IV, differently than that observed when patients were classified in groups according to their MVV.
Conclusion: In COPD patients, MVV better reflects the physical activity level in daily life than FEV(1) and IC.