  Objective: To develop an algorithm that can infer the severity level of a
COPD patient's airflow limitation from tidal breathing data that is collected
by a wearable device.
  Methods: Data was collected from 25 single visit adult volunteers with a
confirmed or suspected diagnosis of chronic obstructive pulmonary disease
(COPD). The ground truth airflow limitation severity of each subject was
determined by applying the Global Initiative for Chronic Obstructive Lung
Disease (GOLD) staging criteria to the subject's spirometry results. Spirometry
was performed in a pulmonary function test laboratory under the supervision of
trained clinical staff. Separately, the subjects' respiratory signal was
measured during quiet breathing, and a classification model was built to infer
the subjects' level of airflow limitation from the measured respiratory signal.
The classification model was evaluated against the ground truth using
leave-one-out testing.
  Results: Severity of airway obstruction was classified as either
mild/moderate or severe/very severe with an accuracy of 96.4%.
  Conclusion: Tidal breathing parameters that are measured with a wearable
device can be used to distinguish between different levels of airflow
limitation in COPD patients.
