MECHANISMS of ACTION
Oxygen inhaled under pressure dissolves in plasma. At 3 atmospheres absolute, an arterial PO2 of nearly 2,200 mmHg may be achieved and up to 6.9 volumes percent of oxygen may be forced into solution, a quantity sufficient to temporarily maintain life in the absence of hemoglobin.
FIBROBLAST PROLIFERATION
Nonhealing tissues are often hypoxic with tissue oxygen tensions frequently in the range of 5 to 15 mmHg. Although low tissue oxygen tensions stimulate fibroblast activity, tissue oxygen tensions of at least 30 to 40 mmHg (optimal tissue oxygen tensions are in the 40 to 90 mmHg range) are necessary for fibroblast proliferation, collagen synthesis, and the development of a collagen matrix to support capillary budding into avascular areas. Raising the tissue oxygen tension in hypoxic wounds can readily be accomplished through the intact peripheral circulation with hyperbaric oxygen therapy.
NEOVASCULARIZATION
Following hyperbaric oxygen sessions, restoration of low PO2 to physiologic levels will stimulate capillary proliferation. The previously stimulted fibroblasts provide a scaffolding and infrastructure to support new capillary ingrowth.
ENHANCEMENT OF WHITE CELL KILLING
Polymorphonuclear leukocytes in low oxygen tensions (e.g., 5 to 15 mmHg) show diminished ability to kill organisms through the peroxidase system (an oxygen-dependent mechanism). The killing ability of white blood cells can be greatly enhanced by increasing tissue oxygen tensions.
VASOCONSTRICTION
Exposure to oxygen at pressure causes a 15 to 25% reduction in blood flow resulting in less diapedesis and bleeding in areas of capillary damage. This effect might seem to be undesirable in ischemic tissue, but the tenfold increase in oxygen content of the plasma and the resultant increase in the capillary diffusion distance of oxygen more than compensates for decreased arterial flow.
ENHANCEMENT OF ANTIBIOTIC ACTIVITY
Evidence shows that certain antibiotics may be more effective in the presence of elevated oxygen tensions. These include aminoglycosides, vancomycin, sulfonamides, and quinolones.