Because in flight, sure to the lowering of barometric pressure at altitudes of more than 30,000 feet, the body tissues can no longer keep atmospheric nitrogen in solution. Due to this and ruptured fat cells, freed gas bubbles enter the circulatory system and may cause obstructions, called emboli, in the blood vessels. One of the most characteristics of the bends are the intense pains in the joints due to lack of blood supply and gas pressure to nerve endings and tendons. A n important part that has a lot to do with Scuba diving and the Bends is the concept of pressure and how it varies in depth. Pressure is defined as force or weight over an area.
All matter has weight due to the earth's gravity .
For example, a column of air one square inch by 50 miles high weighs about 14.7 pounds. This is referred to by divers as pounds per square inch, or psi. This means that every 33 feet pressure increases or decreases. The lower you go the more pressure. For example a diver that goes down 99 feet has three atmospheres of pressure on him.