After obtaining Massachusetts General Hospital Institutional
Review Board approval for the study protocol, patients
with COPD and requiring home oxygen therapy were
recruited. Patients with facial deformities, heavy beards, or
moustaches preventing a good seal between the mask and
the face; those who had claustrophobia and could not wear
the masks; those who were hemodynamically unstable or
pregnant; or those who required continuous, noninvasive,
positive-pressure ventilation were excluded. Sixteen adult
out-patients with documented stable COPD on home oxygen
therapy were enrolled. All provided written informed
consent for the study. The study procedures were performed
in the research laboratory of the Department of
Respiratory Care on the Massachusetts General Hospital
main campus.