Chronic obstructive pulmonary disease (COPD) can affect the small airways and alter respiratory mechanics. Nasal high-flow therapy delivers warmed and humidified gas through nasal cannulas and may change airway resistance. Respiratory oscillometry is a non-invasive test that measures respiratory resistance and reactance during quiet breathing.

This prospective, single-center study will enroll 20 adults with severe or very severe stable COPD who have never used nasal high-flow therapy. During one approximately 6-hour visit, participants will receive individualized nasal high-flow therapy for 4 hours. Oscillometry will be measured before exposure, immediately after device titration, and after 30, 60, 120, 180, and 240 minutes.

The primary objective is to describe the time course of the frequency dependence of respiratory resistance (R5-R20), an indirect index of peripheral airway mechanical abnormalities. Secondary objectives are to describe changes in total and proximal respiratory resistance, respiratory reactance, resonant frequency, and area of reactance. The hypothesis is that nasal high-flow exposure will produce measurable, time-dependent changes in respiratory oscillometry parameters.