altitude /al″tito̅o̅d/ [L, altitudo, height] , the level of elevation of any location on earth with reference to a fixed surface point, which is usually sea level. Several types of health effects are associated with altitude extremes, including a greater intensity of ultraviolet radiation that results from a thinner atmosphere. Barometric pressure decreases as altitude increases, so there are fewer molecules of oxygen. Thus breathing becomes faster and deeper, although demands of physical effort and cellular respiration are the same as at a lower altitude. High-altitude cardiac intolerance is usually worse in people with blood or pulmonary disorders. See also altitude sickness.
