The diaphragm forms a muscular septum between the thorax and the abdominal cavity (Fig 1). It is the most important muscle of respiration.

The nerve supply to the diaphragm is from the phrenic nerves which originate from the spinal cord at cervical level C3, C4 and C5.

The diaphragm contributes to the lower oesophageal sphincter mechanism. This mechanism is disrupted in patients with hiatus hernia. These patients suffer from acid reflux and are at risk from aspiration.