-Lung volume is the total volume the air occupies in lung during respiration. It is also known as lung capacity. -Air pressure is the pressure of the air in the lungs during inhalation and exhalation. During the process of inhalation, the lung volume expands because of the contraction of the diaphragm and intercostal muscles, thus expanding the thoracic cavity. Because of the increase in lung volume, the air pressure is decreased (Boyle’s law) compared to the atmosphere, thus the air enters the airways. During exhalation, the relaxation of the diaphragm and intercostal muscles causes a decrease in the lung volume, resulting in increased air pressure in the lungs compared to the atmosphere, thus the air moves out of the airways.
