(bă-rĭs'ĭ-tĭ )

The relative pressure, density, or concentration of a gas or a solution. Hyperbaric solutions have an increased density relative to a reference substance, e.g., hyperbaric oxygen has a greater oxygen concentration than the air we normally breathe. Hypobaric solutions are less concentrated than a reference solution, e.g., an injected drug can be made hypobaric relative to serum or plasma by diluting it with sterile water.