Technical Overview

Oxygen (02) is a colorless, odorless gas that makes up about 21% of the Earth’s atmosphere.  It is one of the body’s basic building blocks. All the major components of the body (water, protein, carbohydrate, and fat) contain O2.1 Every day an average adult consumes four pounds of food, two pounds of water and almost six pounds of oxygen.  In other words, human beings require about the same amount of oxygen by weight each day as food and water combined.  Of the six pounds of oxygen consumed, about two pounds gets into the blood for transport to tissue cells.

Oxygen drives chemical reactions within the body that involve the production of life-sustaining energy.  A body deprived of O2 will die in a matter of minutes.  Hypoxia, the under-oxygenation of the tissues, results in a reduction in all bodily functions.  Symptoms of hypoxia include mental disturbance, shortness of breath, rapid pulse, low blood pressure, and a blue-black tinge of the skin called cyanosis.

Hyperbaric oxygen therapy (HBOT) is a medical treatment in which a patient breathes 100% oxygen (O2) at pressures greater than atmospheric pressure (sea level) for a short time in an enclosed chamber. Hyperbaric oxygen is chemically the same as found in our atmosphere, but purified from other elements and delivered under pressure.  The increased pressure does not change its molecular composition.

When one breathes through an oxygen mask about five times the normal amount of O2 will reach the body’s tissues.  In a pressurized hyperbaric (HB) chamber 10-20 times the normal amount of O2 reaches the body’s tissues. In about one hour a patient can breathe 2.4 pounds of oxygen.  Red blood cells fill with oxygen, and additionally, the blood plasma is saturated with O2. This extra oxygen stimulates healing.

During the therapy, O2 acts as a drug, eliciting varying levels of response at different treatment depths (amount of pressure), duration, and dosages.  One mechanism of action is to help overcome diseases and conditions that involve a lack of oxygen in the tissues, as normal atmospheric pressure isn’t powerful enough to force oxygen into the tissues. Pathological states involving hypoxia, such as circulatory problems and strokes, can be reversed and rapid healing can take place.

HBOT utilizes the principles of gases and their physiological effects. Normally, oxygen is delivered to tissues and cells by attaching to the hemoglobin in red blood cells.  Usually the hemoglobin is near to 100% saturated with O2 in the lungs when we breathe. (Our atmosphere is about one fifth O2 and four-fifths nitrogen, a small percentage of carbon dioxide and trace amounts of other gases.)

In HBOT oxygen molecules are up to ten times more abundant than they are in the air.  The blood plasma dissolves oxygen when under pressure and the plasma delivers O2 quite easily.  An oxygen-deficient cell may not be in contact with a capillary but is within range, whereas with HBOT the O2 can diffuse from the capillary to the cell and relieve hypoxia.

These fluids carry the extra oxygen to areas where circulation is deficient and/or blocked by defusing into the cells and tissues.  The oxygenation stimulates the healing process, first by enhancing the white blood cells’ ability to fight infection.  HBOT can also encourage the development of new capillaries (angiogenesis) that deliver oxygen under non-hyperbaric conditions (normal atmospheric pressure).  It helps the body renew its tissues and thus promotes healing.2

In most cases, HBOT is not the primary or sole form of treatment.  Usually it is used in combination with physical therapy, drugs, surgery, various types of rehabilitation, etc. Depending on the response of an individual patient and the severity of the presenting problem, treatment may range from less than one week to several months, the average being three to six weeks.

Hyperbaric medicine is a specialized area of medical science that overlaps with diving medicine. For the diver, HBO is the specific cure for Decompression Illness (DCI), and is life saving in the treatment of Air Embolism.  Aviators also suffer decompression illness due to rapid changes in altitude or in pressure and occasionally require HBO therapy.  Due to the serious nature of some HBO responsive diseases, Hyperbaric Specialists tend to also be Intensive Care Medicine Specialists.

Atmospheric pressure is another concept that is key to understanding HBOT.  Because of the Earth’s gravity, the air around the Earth has weight and so it exerts pressure. Atmospheric pressure goes down when one goes up in altitude.  The higher one goes, the less pressure there is.   As one goes down underwater the pressure increases, since water weighs more than air. Water pressure is called hydrostatic pressure, with total pressure being the hydrostatic pressure plus the atmospheric pressure. This total pressure is called absolute atmospheric pressure or atmospheres absolute.

Pressure is measured in pounds per square inch (psi).  Tire pressure, for instance, is measured in psi.  In the case of hyperbaric oxygen the measurement unit used is atmospheres absolute.  The average atmospheric pressure at sea level is 14.7 psi and this is equal to one atmospheres absolute.  Higher pressures are expressed in terms of atmospheres absolute and/or fractions of atmospheres absolute.  2.0 atmospheres means twice the average sea-level pressure.  A prescription of HBOT contains the pressure used, measured in atmospheres absolute, as well as how much time a patient is under pressure, the frequency of treatments, and the total number of treatments.

Notes
1R. Neubauer, (1998). Hyperbaric oxygen therapy. Garden City Park, NY: Avery Publishing Group, 3.
2Ibid., 5.