Abstract
The hallmark of COPD is flow limitation (FL) caused by peripheral airway collapse during expiration. In this case an oscillatory pressure signal applied at the mouth fails to reach the distal airways, creating a within-breath reactance difference. We used forced oscillation technique (FOT) to measure inspiratory-expiratory reactance at 5 Hz, ΔXrs over 30 seconds of resting breathing, and hypothesize that COPD patients with flow limitation have reduced exercise capacity.
Methods
374 COPD patients from the Bergen COPD Cohort study performed FOT, spirometry and 6-minute-walk test (6MWT). 229 controls performed FOT and spirometry. ΔXrs 99th percentile of healthy controls was 0.1 kPa/L/s. COPD patients with ΔXrs exceeding this threshold were defined as likely to experience FL breaths.
Results
FL COPD patients had significantly lower 6MWT than the non-flow limited (NFL), p<0.001. The two groups differed significantly in BMI, MMRC, and FEV1. Separated by GOLD grade significant difference was only found in GOLD 2, though similar trends were seen in GOLD 3 and GOLD 4.
Demographics and 6-minute-walk test
Conclusion
COPD patients likely to experience flow limitation during resting breathing have significantly poorer exercise capability than NFL COPD patients, p<0.001. While FL is more common in advanced disease, GOLD 3-4, significantly differences in the 6MWT was only found in GOLD 2, p=0.02.
- © 2014 ERS
