The Jack Borgenicht Hypoxia/Altitude Physiology Research Facility (JBHARF) operates a normobaric hypoxia chamber at a “normal” sea level atmospheric pressure of approximately 760 torr (1 torr = 1/760 atmosphere or 760 mmHg) which is typical sea level barometric pressure. The facility is actually located at 49 ft. altitude and is usually near 752 torr, approximately sea level depending upon weather conditions. The term “hypoxic” refers to low oxygen tension (in the atmosphere or body tissues). The Hypoxia Chamber of The Jack Borgenicht Altitude Physiology Research Facility can simulate atmospheres found at altitudes up to 18,000 feet. The air units associated with this chamber can extract oxygen from external (normal) air that is then pumped into the chamber and maintain a preset oxygen fraction to simulate a specific altitude while subjects are inside.
The fraction (%) of oxygen (O2) in the atmosphere remains the same at 20.93% regardless of the altitude. At sea level, the atmospheric pressure is 760 torr (equivalent to 760 mm Hg). 20.93% of 760 = 159 torr O2, which is the part of the total atmospheric pressure produced by its fraction of oxygen. The balance is made up of nitrogen, inert gases, and a very small amount of carbon dioxide. At 4,300 meters (14,100 ft.) the barometric pressure is 462 torr and the fraction of the atmosphere made up of oxygen is still 20.93% producing a (partial) pressure of 96 torr. This reduced partial pressure of oxygen pushes oxygen into the bloodstream across a lower gradient resulting in less oxygen carried by the blood to body tissues. This lower oxygen (hypoxia) can result in Acute Mountain Sickness (AMS) and in extreme cases, much more serious illnesses such as High Altitude Pulmonary Edema (HAPE) or High Altitude Cerebral Edema (HACE). It is also interesting that many diseases, both chronic and acute, result in decreased oxygen supply to body tissues (hypoxia). Research that examines the body’s physiological response to hypoxia may be helpful in numerous ways.
Within very narrow limits, the Colorado Altitude Training System (Boulder, CO), allows simulation of various altitudes from sea level to 18,000 feet. By operating the system without filtering out oxygen, the sounds and feel of the chamber are exactly the same at sea level as they are at high altitude. This is imperative when conducting control experiments. Room air is pumped through the 4 air units at a rate of 10L/minute. This air, with its lowered oxygen fraction, is then recycled through the chamber by 3 of the air units while unit 4 introduces fresh room air that has also had its oxygen reduced. This accomplishes two objectives. First, desired altitude is maintained within narrow limits and, second, it is achieved without having to reduce the barometric pressure which would require a very expensive steel chamber in which vacuum pumps reduce the ambient pressure to create “hypobaric” hypoxia