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  • Center for hyperbaric oxygen therapy (HBOT) and diving medicine

How does hyperbaric oxygen therapy work?

Our bodies need oxygen to live. Every single cell of your body uses oxygen to convert sugar and fats into the energy it needs. If oxygen is lacking, the cells cannot sustainably maintain their functions. Having said that, the reasons for any lack of oxygen are diverse and can be both chronic as well as acute.

In addition to diseases of the lungs and the heart, causes for insufficient oxygen supplies to cells can include poisoning (e.g. carbon monoxide poisoning), chronic vascular diseases, overpressure accidents or complicated wounds.

The goal of HBO therapy is to compensate for any local oxygen deficiencies by providing an oversupply of oxygen. This is only possible to a certain degree even when breathing in 100% oxygen under normal pressure.

In order to dissolve more oxygen into the blood, it is necessary to elevate the ambient pressure. Pursuant to Henry’s law (the solubility of a gas in a liquid is proportional to the pressure of the gas over the solution) the patient is subjected to a higher pressure atmosphere and more oxygen is physically dissolved in the blood and transported to the cells.

In order to create a pressure higher than atmospheric air, the patient spends a specific amount of time in therapy in a hyperbaric chamber – in such a session the patient breathes pure oxygen at an elevated ambient pressure.

In this fashion oxygen levels in the body can be achieved (also referred to as arterial oxygen partial pressure) which are several multiples higher than that possible under normal pressure conditions.

This improved oxygen supply enables diseased tissue suffering from oxygen depletion to regenerate over the long term, helping to excite and accelerate the healing processes.

In order to provide tissue threatened by hypoxia with oxygen over longer periods it is necessary for these tissues to create new blood capillaries [1-7]. This is only possible if a high oxygen gradient is created from the edge of the wound to the centre of the wound such that vascular sprouting can take place along the gradient.

As a result new capillaries form in the threatened tissue such that after successful conclusion of the treatment the formally at risk tissue is again sufficiently supplied with oxygen and nutrients. Metabolism is normalised, the tissue heals.

Other positive effects of hyperbaric oxygen therapy

In addition to enriching bodily tissues with oxygen and the new formation of capillaries in deoxygenated tissues, hyperbaric oxygen therapy also results in further physical changes.

Most cell types and processes involved in the wound healing process (e.g. collagen synthesis) require a minimum level of oxygen in order to maintain the functions of cellular metabolism and cell growth [7-9]. Thus hyperbaric oxygen excites and activates the cells in the connective tissues in hypoxic tissues. This in turn creates transformational processes in diseased soft tissue and improves wound healing. Diseased, dying tissue is degraded and new, well perfused tissues are formed by the body’s inherent processes. This effect is today increasingly also used in surgery to treat sensitive flap skin grafts and non-healing wounds.

Hypoxic bone remodelling processes also take place under HBO with both osteoclasts and osteoblasts being activated [10-13]. In this fashion HBO acts in hypoxia-related diseases of the bone tissue to not only encourage an increased rate of necrotic material degradation via the elevated osteoclast activities but also an increased rate of bone formation by the oxygen-induced osteoblast activation. This effect is beneficial in osteomyelitis, aseptic bone necroses and in bone grafts.

The principle of “hyperoxic vasoconstriction” under hyperbaric oxygen therapy is responsible for the reduction of tissue swelling both in soft tissues as well as in bone [14]. In the case of well perfused tissue, the oversupply of oxygen results in a reduction in the flow of blood (vasoconstriction) but without having a negative impact on the tissue because of the greater diffusion distance of the hyperbaric oxygen and the higher oxygen partial pressure. It does, however, result in a reduction in the swelling of all tissues with intact auto-regulation – which in turn improves the tissue supply situation. This positive side effect of the therapy is used to therapeutic advantage in for example treatment of compartment syndrome, endangered skin flap grafts and in bone marrow oedema.

Furthermore, hyperbaric oxygen therapy also encourages the body to strengthen its immune system. In addition to the direct antibacterial effect of oxygen with respect to gas forming bacteria such as clostridia (Clostridium perfringens etc.) this also allows the body’s own immune cells to better destroy pathogens directly [15, 16]. Only when there is sufficient oxygen present can phagocytes such as neutrophils and macrophages actually kill absorbed bacteria by using oxygen radicals. This is not the case in hypoxic wounds, resulting in infections which are difficult to treat. Under HBO conditions, not only is the immune system enhanced, the effects of antibiotics are also strengthened.

The intravascular gas bubbles present in for example decompression sickness or arterial gas embolism are reduced and dissolved by two mechanisms. The higher pressure of the hyperbaric chamber helps reduce the size of the gas bubbles, usually nitrogen gas, by compressing the gas into a smaller volume. The key effect, however, is derived from the nitrogen partial pressure gradient. The inhalation of 100% oxygen results in a higher diffusion gradient for nitrogen (N2), such that it is reabsorbed into solution from the bubble. The bubble disappears.

Hyperbaric oxygen therapy is therefore a highly effective therapy not only for hypoxic tissues with deficient oxygen supply.

References

  1. Knighton, D.R., I.A. Silver, and T.K. Hunt, Regulation of wound-healing angiogenesis-effect of oxygen gradients and inspired oxygen concentration. Surgery, 1981. 90(2): p. 262-70.
  2. Marx, R.E., et al., Relationship of oxygen dose to angiogenesis induction in irradiated tissue. Am J Surg, 1990. 160(5): p. 519-24.
  3. Hopf, H.W., et al., Hyperoxia and angiogenesis. Wound Repair Regen, 2005. 13(6): p. 558-64.
  4. Sheikh, A.Y., et al., Hyperoxia improves microvascular perfusion in a murine wound model. Wound Repair Regen, 2005. 13(3): p. 303-8.
  5. Sander, A.L., et al., In vivo effect of hyperbaric oxygen on wound angiogenesis and epithelialization. Wound Repair Regen, 2009. 17(2): p. 179-84.
  6. Roth, V., et al., Stimulating angiogenesis by hyperbaric oxygen in an isolated tissue construct. Undersea Hyperb Med, 2011. 38(6): p. 509-14.
  7. Lin, K.C., et al., Attenuating inflammation but stimulating both angiogenesis and neurogenesis using hyperbaric oxygen in rats with traumatic brain injury. J Trauma Acute Care Surg, 2012. 72(3): p. 650-9.
  8. Anderson, L.H., et al., Influence of Intermittent Hyperoxia on Hypoxic Fibroblasts. Journal of Hyperbaric Medicine, 1992. 7: p. 103-114.
  9. Kang, T.S., et al., Effect of hyperbaric oxygen on the growth factor profile of fibroblasts. Arch Facial Plast Surg, 2004. 6(1): p. 31-5.
  10. Wu, D., et al., Effects of hyperbaric oxygen on proliferation and differentiation of osteoblasts from human alveolar bone. Connect Tissue Res, 2007. 48(4): p. 206-13.
  11. Yuan, L.J., et al., Effects of low-intensity pulsed ultrasound and hyperbaric oxygen on human osteoarthritic chondrocytes. J Orthop Surg Res, 2014. 9: p. 5.
  12. Tripathi, K.K., et al., Effect of hyperbaric oxygen on bone healing after enucleation of mandibular cysts: a modified case control study. Diving Hyperb Med, 2011. 41(4): p. 195-201.
  13. Sever, C., et al., Effect of hyperbaric oxygen therapy on bone prefabrication in rats. Acta Orthop Traumatol Turc, 2010. 44(5): p. 403-9.
  14. Nylander, G., et al., Reduction of postischemic edema with hyperbaric oxygen. Plast Reconstr Surg, 1985. 76(4): p. 596-603.
  15. Zanon, V., et al., Oxybiotest project: microorganisms under pressure. Hyperbaric oxygen (HBO) and simple pressure interaction on selected bacteria. Med Gas Res, 2012. 2(1): p. 24.
  16. Almzaiel, A.J., et al., Effects of hyperbaric oxygen treatment on antimicrobial function and apoptosis of differentiated HL-60 (neutrophil-like) cells. Life Sci, 2013. 93(2-3): p. 125-31.





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