What is Hyperbaric Medicine?

It is a little known field of Medicine that harnesses the healing powers of oxygen when applied at pressures greater than atmospheric pressure. Sounds magical,right? Well through the undaunting efforts of Undersea and Hyperbaric Medicine society, this wonderful treatment has found a firm footing in modern day medicine. The interested reader may find further information here. SOURCE.

What happens to oxygen as it enters the body at pressures greater than atmospheric pressures?

We breathe in atmospheric oxygen under usual circumstances at sea level which is 760 mm of mercury ( Hg) or 1 ATM ( one atmosphere). So 760 mm Hg = 1 ATM. An excellent derivation can be found here. For the purposes of this post instead of ATM you can also use ATA interchangeablely. ATA is atmospheres absolute. There are minor differences between sea level pressure and pressure at the top of a high mountain. For example if you go up to the mountains in Denver from sea level, you may be breathing air at 0.8 ATM rather than 1 ATM.
In the human body, we breathe in air at 1 ATM at sea level. Approximately 20.9% of this is oxygen which is the molecule of our concern. This oxygen goes through the alveoli ( little lung units that look like little sacs) into the blood capillaries surrounding the alveoli.
SOURCE.
The oxygen encounters hemoglobin molecule within red blood cells and one hemoglobin molecule is able to carry 4 diatomic oxygen molecules. Most of the oxygen is transported in this fashion to the tissues. The part of blood without cells is called plasma. Very very small amounts of oxygen is dissolved in plasma. This is the second way blood carries oxygen. SOURCE. Hemoglobin bound oxygen transport accounts for about 97% of oxygen transport. SOURCE. When the partial pressure of oxygen in blood is about 100 mm Hg which is the usual approximate value breathing room air at sea level, only 0.3 ml of oxygen per 100 ml of blood is carried in the plasma.SOURCE. Thus under usual circumstances of breathing only negligible amounts of oxygen is carried in plasma and most oxygen transport is hemoglobin based.

Under conditions of pressure higher than atmospheric pressure also known as HYPERBARIC CONDITIONS, oxygen transport goes through a radical change. We learned above that under normal circumstances of 1 ATM, the partial pressure of oxygen in blood or Po2 is about 100 mm Hg. At 2.5 ATM while breathing 100% oxygen the Po2 rises to 1804 mm Hg. SOURCE. This enormous amount of oxygen causes beneficial effects on diseased tissue as discussed below.

The Hyperbaric chamber.

SOURCE
In a hyperbaric chamber, after placing the patient, 100% oxygen is bled in to the desired pressure, say 2 ATM or 2.5 ATM. This increases oxygen delivery to the diseases tissue several hundred folds as noted above. This oxygen enriched environment produces some astounding effects. There are different mechanisms of actions for the various disease conditions in which hyperbaric oxygen serves a purpose. I will discuss one below briefly.

Hyperbaric Medicine in Diabetic ulcers/wounds.

A diabetic ulcer is notoriously difficult to heal. Improper circulation is often a problem. If a large artery is blocked then lack of oxygen to the tissue is of major concern. That patient will NOT be helped by Hyperbaric treatments as even though the blood is oxygen enriched, that blood cannot reach the diseased tissue. Corrective vascular surgery is needed. On the other hand if the major vessels are okay but the small vessels are diseased then there is no corrective surgery. This is the case for many with diabetic ulcers. Hyperbaric oxygen therapy was tested for treatment of chronic diabetic foot ulcers in a clinical trial called HODFU. 52% of patient’s treated with Hyperbaric oxygen therapy achieved complete wound healing. SOURCE. Hyperbaric oxygen therapy is known to cause angiogenesis. [REFERENCE 1]. It is also known to increase growth of fibroblasts. [REFERENCE 2]. Angiogenesis is the formation and proliferation of new blood vessels.Fibroblasts produce extra cellular matrix and collagen. SOURCE. Thus connective tissue is formed that has new blood circulation and tissue is healed. Patients have to undergo several sessions in a Hyperbaric chamber. Each session lasts over an hour. It is a slow process but many achieve wound healing. This prevents many amputations.

Fibroblast: SOURCE

Other indications for Hyperbaric oxygen treatment.

I will list a few here. A complete list is available here. SOURCE.

• Decompression Illness also known as Bends.
• Gas Gangrene.
• Carbon Monoxide poisoning.

REFERENCES:
1.Reng JJ, Hussan MZ, Constant J, Hunt TK : Angiogenesis in wound healing. J Surg Pathol 1998; 3: 1– 7
2.Brismar K, Lind F, Kratz G : Dose-dependent hyperbaric oxygen stimulation of human fibroblast proliferation. Wound Repair Regen 1997; 5: 147– 150