Under the influence of phrenic nerve input, the diaphragm contributes more than any other muscle to inspiration. At rest, the domes of the diaphragm descend to decrease intrathoracic pressure; simultaneously, the intraabdominal pressure is raised. With the intrathoracic pressure now less than the extrathoracic pressure, air is drawn inwards.
With deeper respiration, there is more extensive descent of the domes which brings them inferior to the central tendon. The tendon is drawn down by approximately one vertebral level with similar descent of the overlying and adherent pericardium.
With a maximal inspiration, the pull on the costophrenic angle is such that the costal margin is drawn superolaterally.
Inspiratory movements by the diaphragm facilitate the circulation of blood from abdomen to thorax by:
The hiccup is in part due to the same diaphragmatic contracture as during inspiration.
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