Definition of Ventilation Ventilation is the process of moving gases through the respiratory tract. The contraction of these muscles increases the volume of the chest cavity, lowering the pressure inside. As the pressure in the airways decrease, air rushes in as the chest volume increases. As the muscles relax, the elastic recoil of the lungs puts pressure on the gases inside. The pressure in the chest is now higher than outside pressure, so air rushes out.
Expiration stops when the recoil of the lung and the spring of the ribs balance each other.
The muscles of the chest wall, including the diaphragm, contract to expand the volume of the chest. This vacuum is transmitted through the fluid-filled pleural space, lowering the pressure in the air sacs of the lung. This draws air in. As the muscles relax, the elastic recoil of the lung pushes air back out. Back to Index.