FUNDAMENTALS OF HYPERBARIC MEDICINE

Hyperbaric Oxygen Therapy consists in breathing O2 near to 100% within a pressurized chamber above the normal atmospheric pressure. For clinical use, the pressure should be at least 1.4ATA. Hyperbaric oxygenation (HBO) is used as a primary therapy, in certain diseases and intoxications, or as an adjunctive therapy in pathologies with inadequate oxygen supply to the tissues.

Hyperbaric chambers are medical devices where HBOT is performed in a non-invasive and safe fashion: high O2 concentration is administered to the patient by means of a mask, within a pressurized environment. In order to understand how this therapy works, it is important to keep in mind the main function of the breathing process: oxygen enters the body, to be distributed throughout the circulatory system to all organs and tissues.

How can we ensure that all tissues and cells receive O2 during HBOT? The answer follows the Krogh model. This model considers capillary density in tissues, capillary radius and distance between tissue cells and capillaries, to calculate the O2 diffusion and penetration distances. It also explains the existence of pressure gradients (PpO2) depending on the capillary radius and on the arterial and venous ends of the microvasculature. Considering all these variables, the model predicts tissular PpO2: administering O2 near to 100% in an environment under 1.4ATA, the O2 penetration radius from capillaries to tissues is ~75 μm. Under hyperbaric conditions (equal or greater than 1.4ATA) O2 reaches, and even considerably exceeds, the penetration baseline (~40 μm) required to attain the minimum effective PpO2 (20mmHg), satisfying cellular functions.

The HBOT produces hyperoxia and temporary increase the production of ROS. Thus, it solves adverse conditions such as hypoxia and edema, and promotes normal physiological responses or responses against infectious and ischemic processes. Additionally, HBOT stimulates the expression and activity of antioxidant enzymes, to maintain homeostasis and the redox cellular state (reductive/oxidative) and ensure treatment safety.

Among the mechanisms promoted by HBOT, we can include:

– Vasoconstriction. This effect is favored by increasing available O2 in small arteries and capillaries. Vasoconstriction occurs in healthy tissue without deterioration in oxygenation, promoting flow redistribution to hypoperfused areas.

Angiogenesis. Hyperoxia stimulates neovascularization, or the formation of new vessels, by two different processes: vasculogenesis and angiogenesis.

Osteogenesis. Hyperoxia stimulates cell differentiation, formation of mineral deposits and phospho-calcium metabolism.

Cellular immune response against infections. In adverse conditions such as hipoxia, susceptibility to infections increases. In hyperoxia, some immune cells such as neutrophils or polymorphonuclear cells (PMN) respond to pathogenic noxa exerting its bactericidal action, through ROS and FR production and peroxidase enzymes activity. Furthermore, HBOT exerts synergistic action with some antibiotics facilitating O2-dependent transport through the bacterial cell wall.

Anti-inflammation  and  edema  reduction.  Vasoconstriction  helps  to  reduce  the inflammatory response and therefore to reduce edema.

Wound healing. Along with stimuli which promote collagen synthesis and neovascularization, hyperoxia also stimulates the formation of granulation tissue in regions affected by adverse conditions. Through the synergy between these  mechanisms, the process of wound healing is accelerated.

Neuroprotection. In addition to improved perfusion from the formation of new blood vessels and brain oxygenation, hyperoxia increases neuroplasticity and stimulates peripheral axonal regeneration.

Sources:

  • Oxigenación Hiperbárica: Fundamentos, Mecanismos bioquímicos y aplicaciones. Mariana Cannellotto (Directora Médica), Irene Wood* (Doctora en Bioquímica)
  • Society, U.a.H.M., HYPERBARIC OXYGEN THERAPY INDICATIONS: 13th EDITION 2013. Tibbles , P.M. and J.S. Edelsberg Hyperbaric-Oxygen Therapy.

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