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Basic Science

HYPERBARIC OXYGEN THERAPY.

'INTERMITTENT, SHORT TERM, HIGH-DOSE OXYGEN INHALATION'

Hyperbaric oxygen Therapy (HBOT) is a technique which allows patients to breathe pressurised 100% oxygen through a hood or mask while in a compressed air chamber. Such exposure results in a large increase in the partial pressure of oxygen in the plasma and increased oxygen delivery to tissues and bone.

HBOT BENEFITS INCLUDE:

  • Hyper-oxygenation of the blood
  • Fibroblast Proliferation and Enhanced Function
  • Neovascularization
  • Direct antimicrobial action of high oxygen
  • Enhancement of leukocyte function
  • Decreased edema
  • Enhancement of some antibiotic activity
  • Compression of bubbles
THE SCIENCE.
 
Modern Hyperbaric Oxygen (HBOT) treatment involves the patient breathing pressurised, pure oxygen through a clear hood or a mask while seated in the equally pressurised, but normal-air atmosphere of the hyperbaric chamber.

Both the pure oxygen and the normal air are at the same pressure - between 2.0 and 2.8 atmospheres. The normal air in the HBO chamber reduces safety risks and means attendant staff can be present at all times.

The effect of breathing 100% oxygen at this pressure is to increase the  amount of oxygen a patient normally breathes by ten to twenty times resulting in a 10-15 fold increase in plasma oxygen concentration. This produces a significant increase in the diffusing distance of oxygen from functioning capillaries.  The arterial oxygen values  reach between 1,200 and 1,800 mmHg during treatment, whereas normal values are around 80-100 mmHg.

Growth of new blood vessels or neovascularisation, is enhanced by increased plasma oxygen.  This effect is only seen in areas of impaired new vessel formation such as late radiation damaged tissue, refractory osteomyelitis and chronic ulcerations in soft tissue.

Hyperbaric oxygen has also demonstrated antimicrobial activity at several levels. It causes toxin inhibition and toxin inactivation in Clostridial perfringens infections (gas gangrene). Hyperoxia enhances phagocytosis and white cell oxidative killing and aminoglycocide activity and prolongs the post-antibiotic effect when hyperbaric oxygen is combined with tobramycin against Pseudomonas aeroginosa.

HBO treatment for 11 conditions is currently funded in Australia; 6 conditions by Medicare and others by various medical insurers.

RATIONALE

Hyper-oxygenation of the blood elevates the amount of dissolved oxygen and results in the correction of tissue hypoxia. This results in improved or enhanced wound healing, infection control, alleviation of tissue ischemia and the dissociation of carboxyhemoglobin.

An oxygen pulse of approximately 2 hours daily enhances fibroblast migration and mitosis. High lactate (originating in the wound) and hyperoxia also combine to induce greater collagen synthesis.

Increased fibroblast collagen synthesis enhances capillary growth, which further raises the partial pressure of oxygen in an incremental fashion as neovascularization progresses.

Direct toxicity to anaerobic bacteria.

The second method of infection control is an indirect effect by the enhancement of WBC killing of phagocytized bacteria. Elevated oxygen increases the oxygen free radicals and hydrogen peroxide formation in the white cell lysosomes, improving their antimicrobial activity.

In inflamed and edematous tissue, HBOT leads to constriction of blood flow which can reverse the fluid loss into the tissues and reinstate normal lymphatic drainage. Also, HBOT appears to improve capillary integrity reducing leakage.

Selected drugs become more effective with normalisation of tissue oxygen or high partial pressure of oxygen.



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