Abdominal and intercostal muscle activation pattern during exposure to hypoxia and ischemia

The coordination of respiratory muscle activity is essential to move air in and out of the lungs. At rest, inspiration is an active process with contractions of diaphragmatic (DIA) and external intercostal muscles (eIC) that generate the inspiratory airflow. In contrast, the expiratory airflow is passively generated by elastic recoil forces of the thorax and lungs. Exposure to reduced oxygen or elevated carbon dioxide levels transforms expiration into an active process, with the recruitment of abdominal (ABD) and internal intercostal muscles (iIC) that increase the expiratory flow. It remains unclear how the ABD and iIC muscles are coordinated during active expiration and how their entrainment modifies the expiratory flow to improve pulmonary ventilation.