Effects of pressure change on body gasfilled cavities

The gas contained in the body cavities is effected by external pressure change، thus with decreasing atmospheric pressure، during ascent or loss of cabin pressure، the gas volume increases and during descent the volume of the gas decreases. The connection with the external environment is achieved in different manners for different cavities. During external pressure change the gas pressure inside the cavities has to reach equilibrium with the air pressure outside. In this review، the gas expansion and the theories of its effect on body cavities are discussed and the body cavities and classified in two distinct categories: Semi-closed cavities and closed cavities. The middle ear، the paranasal sinuses and the lungs are studied in the former and the alimentary canal and the teeth are discussed in the latter.