Diaphragmatic Ultrasound in Critically Ill Patients

The diaphragm is the most important inspiratory muscle. It is dome-shaped, with the crural portion inserted on the anterior portions of lumbar vertebrae 1 through 3, and the costal portion inserted on the xiphoid process and the upper, inner margins of the lower six ribs. The majority of the muscular portion of the diaphragm lies directly beside the lower rib cage, referred to as the zone of apposition (ZOA) (Fig. 1a).