What Pressure of the air inside lungs?

The pressure of the air inside the lungs varies during the respiratory cycle. During inspiration (breathing in), the pressure in the lungs decreases to below atmospheric pressure, causing air to flow into the lungs. During expiration (breathing out), the pressure in the lungs increases above atmospheric pressure, forcing air out of the lungs.

The difference between the pressure in the lungs and the atmospheric pressure is known as the transpulmonary pressure. The transpulmonary pressure is generated by the contraction of the diaphragm and the muscles of the rib cage. The diaphragm is a dome-shaped muscle that separates the thoracic cavity from the abdominal cavity. When the diaphragm contracts, it pulls the lungs downward, which increases the volume of the thoracic cavity and decreases the pressure in the lungs. The muscles of the rib cage also contribute to the transpulmonary pressure by elevating the ribs, which increases the volume of the thoracic cavity.

The normal atmospheric pressure at sea level is 14.7 pounds per square inch (psi). The pressure in the lungs during inspiration is typically about 4 psi, and the pressure in the lungs during expiration is typically about 0 psi. The transpulmonary pressure during inspiration is therefore about 10 psi, and the transpulmonary pressure during expiration is about 4 psi.