Physiological Effects of Altered Barometric Pressure

Abstract

Scientists of the twentieth century have been fortunate to participate in the most exciting period of discovery in human environmental physiology. New biomedical knowledge coupled with a technological revolution has given human beings the opportunity to visit and explore the depths of the ocean and the frontiers of space. Such extreme environments present the physiologist with the challenge of defining reasonable parameters for physiological tolerance so that life support systems can be engineered to maximize our opportunity to interact with the environment. Among the most troublesome environmental factors are heat and cold, exposure to radiation, effects of acceleration and microgravity, hypoxia and hyperoxia, and extremes of barometric pressure. Nonetheless, humans can survive for many weeks or months in many exceptional environments ranging from high altitude near the vacuum of space to simulated undersea depths of more than 70 atmospheres of pressure absolute (ATA). Abrupt or extreme changes in barometric pressure account for many of the injuries and deaths connected with the practice of aviation and diving. Physiological problems arise most commonly in association with rapid decompression from a higher pressure to a lower one, such as rapid ascent from depth under water, or to high altitude. These problems may arise from technical or procedural failures and from our incomplete understanding of inert gas transport and gas elimination from body tissues. High-pressure environments have an important role in modern society for many reasons. The earliest engineering application of high pressure, to maintain dry working conditions in caissons and tunnels, continues today, and it extracts a toll in decompression sickness and aseptic bone necrosis from workers who undergo daily decompression after long shifts in compressed air. As the demand to exploit undersea resources such as oil has increased, so has the working depth and time, and hence the medical vulnerability, of the diver. In relatively shallow diving with air and mixed gases, many commercial and military divers rely on surface supplied gear to provide respirable gas and continuous communication with surface tenders. These diving rigs provide an unlimited supply of breathing gas to the working diver in open, semiclosed, or closed (rebreathing) circuits. In addition, thousands of commercial, military, and scientific divers also have been trained to use self-contained underwater breathing apparatus (SCUBA) to work in shallow water. For some 50 years, the availability of lightweight, open-circuit SCUBA and low-resistance regulators has opened up recreational diving possibilities for thousands of sports divers. Finally, the growth of therapeutic hyperbaric oxygen as well as and the need to provide recompression therapy to the injured diver results in the routine exposure of patients, physicians, nurses, and other medical personnel to hyperbaric environments. Keywords: Barometric pressure; Pressurized environments; Hyperbaric chambers; Submarines; Diving; Physiological effects; Narcosis; Oxygen toxicity; Decompression; Hyperbaric oxygen; Fitness; SCUBA