What Does the Doctor Mean when They Prescribe 1 or 2 Atmospheres?

There is another aspect that must be considered on and beyond the usual physiological role of oxygen in the body. This other aspect relates to the delivery of oxygen to the body under hyperbaric pressures. The term hyperbaric literally means high pressure. A person living at sea level is at one atmosphere of air pressure absolute (ATA). This can be expressed as 760 mm (or 29.9 inches) or mercury, or 14.7 pounds per square inch of air pressure. These numbers express the weight (or measure) of the vast envelope or "ocean" of air that surrounds the globe. We live at the bottom of this air layer. This air pressure is not noticeable because it is equally distributed over the body.

Because of the various physical laws governing temperature, pressure and volume of gases, it was discovered that if the partial pressure of oxygen coming in contact with alveolar capillaries was increased there was a corresponding increase in the amount of oxygen that will be forced into solution in the blood. Since the hemoglobin of the red blood cells is already 98% saturated, the only place the additional oxygen can go is in the plasma. At one ATA* of pressure (the standard air pressure or sea level), the partial pressure of oxygen in alveolar air amounts to about 673 mm of mercury (mmHg). However, when a person is placed in a hyperbaric chamber and delivered pure oxygen at 2 atmospheres (ATA)1 (or 1520 mm of mercury) the alveolar oxygen pressure will increase to about 1433 mm of mercury. At 3 ATA or 2280 mmHg the alveolar oxygen pressure increases to 2193 mmHg. Theoretically, arterial and tissue oxygen pressure closely follow alveolar oxygen pressure. This is a dramatic increase in the amount of oxygen going into the blood.

When the body is at rest, it normally consumes about 6 ml of oxygen per 100 ml of blood, but of this amount only 0.3 ml is transported by the hemoglobin in the red blood cells. When the hyperbaric pressure is raised to 2 ATA of pure oxygen, the plasma oxygen is raised to 4.4 ml. Thus, oxygen saturation of the tissues is considerably enhanced with the use of hyperbaric oxygen therapy. At 3 ATA approximately 6.4 volumes per cent of oxygen are physically dissolved in the plasma, which is sufficient to sustain life even in the absence of hemoglobin.

In brief, the beneficial effects derived from hyperbaric oxygen therapy are due to: 1) the role of oxygen in energy production within the cells of the body, and 2) the availability of adequate quantities of oxygen to the tissues of the body because of a pressurized system operating at optimum levels. Keep in mind that hyperbaric oxygen therapy is used in those diseased conditions

*ATA is a term used to define the amount of pressurization used within a Hyperbaric Oxygen Chamber and refers to Atmospheres of pressure.

Absolute: In a space where a vacuum exists the pressure is spoken of as zero Atmospheres Absolute. At sea level the air pressure is one Atmosphere Absolute.

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