ED	exertional desaturation
COPD	chronic obstructive pulmonary disease
HRs	hazard ratios
DLCO	diffusing capacity of the lungs for carbon monoxide
6MWT	6 minute walking test
hsCRP	serum high-sensitivity C-reactive protein
V	ventilation
Q	perfusion ratio
MMRC	Modified Medical Research Council dyspnea scale
BMI	body mass index
BODE	body mass index, airflow obstruction, dyspnea, and exercise capacity
FVC	forced vital capacity
FEV1	forced expiratory volume in 1 s
RR	respiratory rate;
SpO2	oxyhemoglobin saturation by pulse oximetry.