Chronic obstructive pulmonary disease (COPD) causes breathing difficulty. COPD is a group of lung conditions that includes chronic bronchitis and emphysema. Both conditions are characterized by restriction of airflow. The inability to get enough oxygen to the lungs raises your risk for developing hypoxia. Hypoxia is a condition marked by an inadequate oxygen supply to the cells and tissues of the body. It can lead to a number of serious, sometimes life-threatening, complications.