## TABLE 1924 Pressure Volume Relationships According to Boyles

Because body tissues are composed mostly of water, which is not compressible, they are not directly affected by pressure changes. However, gases are compressible, and, consequently, gas-filled organs of the body are directly affected by pressure changes.

GAS LAWS Diving physiology is largely explained by three gas laws.

The first is Boyle's law, which states that the volume of a gas is inversely proportional to its pressure at a constant temperature. This is expressed by the equation.

where P is pressure, V is volume, and K is a constant. Thus, as shown (see Table 19.2.-4), when the pressure is doubled the volume of a unit of gas is halved, and conversely when the pressure is decreased in half, the volume doubles. Boyle's law explains the basic mechanism of all types of barotrauma.

The second is Dalton's law, which states that the pressure exerted by each gas in a mixture of gases is the same as each gas would exert if it alone occupied the same volume, or, alternatively, the total pressure of mixture of gases is equal to the sum of the partial pressures of the component gases. This is mathematically stated as 