Hyperbaric Oxygen And Hyperoxygenation
Hyperbaric oxygen is 100% pure oxygen used as a drug under increased atmospheric pressure maintained inside a sealed Hyperbaric Chamber. Hyperoxygenation of body tissues is a major instrumental function of the Hyperbaric Oxygen Treatment.
The primary mechanism of Hyperbaric Medicine is governed by physical laws described by Charles, Boyle and Henry, also known as an ideal gas laws. Thus for example, summarizing interrelation between gases, liquids, temperature and pressure, Henry law explains the physical reason for hyperbaric oxygenation:
If atmospheric pressure increased, more oxygen is dissolved into body fluids than it would be seen under the normobaric pressure.
Normobaric Oxygenation
The life actually occurs at a cellular level. Oxygen is the most essential element in biochemical and physiologic processes enabling vital aerobic cellular respiration.
Tissue oxygenation is a process which starts in the lungs’ alveoli and pulmonary capillary system where blood and plasma saturate with oxygen taken from the inspired air (see the respiratory system diagram).
Normally our tissues consume oxygen delivered by haemoglobin, an amazing multi-task-performing molecule of blood. Haemoglobin molecules are carried in our bloodstream by red blood cells, erythrocytes.
The arterial oxygen saturation (SaO2) is proportional to an individual’s binding capacity of haemoglobin. SaO2 is usually measured by noninvasive method, pulse oximetry, but it can also be measured by testing arterial blood gas. Abnormal arterial oxygen saturation can lead to a tissue hypoxia.
Adequate tissue oxygenation under normobaric conditions, e.i. under a normal atmospheric pressure, indicates that a delivery rate of oxygen transported from the lungs to the peripheral tissues satisfies their metabolic requirements.
Oxygen consumption is a rate at which oxygen is dissolved from the blood and plasma for use by the tissues. Our body tissues at rest usually consume 5-6 mL of oxygen per deciliter of blood. The image below illustrates haemoglobin binding process.
However there is a physiologic maximum restricting the blood's carrying capacity of oxygen to a certain extent: 1g of haemoglobin binds only up to 1.34 cm3 of oxygen. Illness or injury tends to compromise oxygen-carrying capacity of blood.
Under normobaric conditions at sea level the air we breathe includes approximately 19-21% of oxygen. 97.5% of that oxygen is transported by haemoglobin and 2.5% only carried by blood plasma. The video below illustrates the normal oxygenation process...
The role of blood plasma as the oxygen carrier under the normal (normobaric) atmospheric pressure is quite minor and tissues oxygenation mainly depends on a binding capacity of haemoglobin.
Here is a healthy tissue oxygenation under normal atmospheric pressure:
Hyperoxygenation
Inside Hyperbaric Chamber with the increase of atmospheric pressure, in addition to the normal haemoglobin saturation, the oxygen concentration in plasma, lymph and cerebrospinal fluid starts to raise reaching up to 6 mL/dL level (this is governed by general laws of gas dissolved in liquids mentioned above).124
Photo courtesy of E-Mans av8pix.com
The consequences of hyperoxygenation are of a great significance:
- The total oxygenation of body inside hyperbaric chamber now equals to a maximum oxygen-carrying capacity of haemoglobin plus up to 2000% increase of oxygen concentration in plasma and other body fluids
- Plasma saturated with oxygen does not just enhance the oxygen-carrying capacity of haemoglobin. Reaching concentrations of up to 6 mL/dL (at a pressure of 3 atmospheres) oxygen dissolved in plasma exceeds metabolic requirements of tissue and bone cells regardless of haemoglobin supply 223
- Oxygen carried by plasma is capable to reach destinations in oxygen deprived tissues or bones otherwise unavailable to red blood cells carrying haemoglobin molecules
In other words, hyperbaric oxygen can safely “by-pass” or “disregard” the "ill" state of what normally serves as the main oxygen delivery transport - the haemoglobin. In healing some acute health conditions such as an exceptionally severe anaemias or carbon monoxide poisoning this property of hyperbaric oxygen plays a crucial role. This outstanding ability of hyperoxygenation constitutes the essence of Hyperbaric Medicine.123, 124, 125
In the hypoxic wounds, hyperoxygenation improves the pathophysiology associated with oxygen deficiency and impaired wound healing. A key factor in hyperbaric oxygen treatment's enhancement of the hypoxic tissues is its ability to establish adequate oxygenation levels within the vascularised connective tissues surrounding hypoxic sites.
The following graph presents an example of a baseline ulcer tissue oxygenation at room air concentration, then after 20 min exposure to 100% oxygen at 1 atmosphere absolute (1 ATA) and finally after 20 min exposure to 100% oxygen at 2 ATA. The ulcer tissue oxygenation was evaluated by transcutaneous O2 pressure (TCpO2) measurements using a pulse oximeter.
Hyperoxygenation results in an improved leukocytes function when killing bacteria, improved antibiotic effectiveness, and an enhanced collagen synthesis.
Additional positive effects of hyperoxygenation may persist even after the completion of hyperbaric oxygen treatment. Among them are: prevention of leukocyte activation and adhesion following ischaemic reperfusion, blunting of systemic inflammatory responses, inhibition of bacterial toxin synthesis, etc.
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