During pulmonary ventilation, relaxation of the diaphragm and external intercostals and air flows out of the lungs. increases the pressure in the thoracic cavity flattens the floor of the thoracic cavity increases the volume of the thoracic cavity expands the rib cage stimulates the phrenic nerve

Increases the pressure in the thoracic cavity

Explanation:

During pulmonary ventilation, relaxation of the diaphragm and external intercostals increases the pressure in the thoracic cavity and air flows out of the lungs.

Pulmonary ventilation involves the exchange of air in the body. The exchange mainly takes place between the lungs and the the blood. When the lungs take in oxygen it distributes it to other parts of the body after which the byproduct is expelled in the form of Carbon dioxide.

The diaphragm and intercostal muscles are found close to the chest(thoracic) region such that when air is expelled it produces a similar effect such as relaxation of the diaphragm which also makes the chest muscles go down and exert pressure. This mechanism aids the expulsion of Carbon dioxide from the lungs.