Aerospace Pressure Effects - PubMed (original) (raw)
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In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2026 Jan.
2022 Oct 24.
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- PMID: 29262037
- Bookshelf ID: NBK470190
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Aerospace Pressure Effects
William J. Tarver et al.
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Excerpt
Human exposure to hyperbaric pressure occurs while diving and during hyperbaric oxygen therapy. Hypobaric exposures occur on commercial plane flights where the cabin pressure equals about 2438.4 meters (8000 feet); however, professional aviators, particularly military personnel, mountain climbers, research subjects, and astronauts, are exposed to much greater extremes in low-pressure environments. The 2 main concerns about hypobaric exposure relate to absolute pressure upon the human body and the total oxygen available.
Gas Laws
Understanding the gas laws is foundational to understanding how pressure changes affect humans. The gas laws describe the relationship between temperature, volume, and pressure for a given amount of gas.
Charles's law
Charles's law states that the volume is proportional to the temperature for a given pressure. Therefore, a gas expands when heated as the pressure remains the same. However, if gas cannot expand, such as when trapped inside the middle ear or a nasal sinus, the pressure increases. For a given volume, the pressure varies with the temperature of the gas. The thermoregulatory system in the human body does not typically allow for more than a few degrees Celcius variance in body temperature.
Boyle's law
Boyle's law states that the volume is inversely proportional to the pressure for a given temperature. This law explains why sinuses or the middle ear (normally fixed-volume gas-filled spaces) may hurt during altitude or pressure changes.
Dalton's law
Dalton's law notes the total pressure of a mixture of gases equals the partial pressure exerted by each gas. This concept is important given that humans breathe air as a mixed gas of nitrogen (~78%), oxygen (~21%), and trace other gases.
If the human body is exposed to a low enough absolute pressure, then surface fluids (tear film, saliva, and the air-exposed surface of alveoli) begin to boil at normal body temperature. This occurs around 60,000 feet (~11.4 miles or 18.3 kilometers), depending on exact atmospheric conditions. This altitude was named "Armstrong's limit" or "Armstrong's line" after an early American aerospace medicine physician, Harry G. Armstrong. When blood boils, this is called "ebullism" and is the trapping of gases released from blood under the skin. Ebullism is painful but recoverable to full function, as human experience has shown.
Reduced Oxygen Levels
Reduced oxygen levels in the body can occur for various reasons. Hypoxia is the general term for low oxygen content in the blood or at the tissue level. Hypoxic hypoxia is hypoxia secondary to low alveolar oxygen exchange in the lungs. It can be caused by either a low oxygen availability or a low surface area for the gas exchange. In this article, "hypoxia" means hypoxic hypoxia due to low environmental oxygen availability. While the percentage of oxygen remains constant at 21% as one increases in elevation, the total pressure of oxygen decreases because the total pressure of all gases combined decreases. The barometric pressure at sea level is around 760 mm Hg, with some variation depending on the weather. Therefore, oxygen is only 21% of that total or 160mm Hg at sea level. Inside the lungs and alveoli, the temperature remains approximately 37 degrees Celsius (98.6 degrees Fahrenheit). As one ascends altitude, the total atmospheric pressure decreases, which means the oxygen available for breathing also decreases.
While there is some variation from person to person, the effects of hypoxia are accepted to begin at 3048 meters (10,000 feet). These effects include reduced light reception and decreased ability to distinguish colors. As a person ascends altitude, their body compensates with increased depth of respiration, increased rate of respiration, and increased heart rate to maintain oxygen delivery to the tissues. Further, ascent leads to extreme fatigue and reduced mental capacity. Exposure to atmospheric conditions in approximately 7620 to 10,363 meters (25,000-~34,000 feet) results in death if supplemental oxygen is not used. Under 34,000 ft, 100% oxygen in a tight-fitting mask delivers near-ground-level oxygen to the tissues. Pressure suits or pressurized cockpits must be used beyond this level to maintain near-sea-level tissue oxygenation.
Copyright © 2026, StatPearls Publishing LLC.
Conflict of interest statement
Disclosure: William Tarver declares no relevant financial relationships with ineligible companies.
Disclosure: Keith Volner declares no relevant financial relationships with ineligible companies.
Disclosure: Jeffrey Cooper declares no relevant financial relationships with ineligible companies.
References
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