Altitude, The Hyperoxic Hypoxia Paradox, and The Common Sense Paradox
You may ask what altitude has to do with HBOT. The answer is simple enough, the same physics apply to altitude considerations as they do to increasing pressure considerations.
Note: Hyper-baric is the increase of ambient pressure and hypo-baric is the opposite, the reduction of ambient pressure.
The physics for altitude related physiological changes and processes is universally accepted. It is also well known that altitude sickness and hypoxia induced symptoms mimic the hypoxia induced symptoms in injury and illness. When climbers, balooners, pilots in open cockpits etc go to elevated altitudes, they experience lower air/atmospheric pressure and they can suffer altitude sickness. In short, they suffer from hypoxia, a lack of, or insufficient oxygen in the tissues. In severe cases and untreated this can lead to brain damage, loss of vision, disability and even death. This is the reason for the pilot’s mask, the balooners emergency oxygen and a climbers pressure bag or Gamow Bag as they are known.
It’s common knowledge to climbers and non-climbers alike, or those who have even just watched a film about climbing, that when this happens the only solution is to increase the amount of oxygen reaching the tissues. The same was discussed under anaemia, wound healing and so on. It’s all about low oxygen or hypoxia. The prescribed treatment for lack of oxygen is to give more oxygen to the tissues. There is a point at altitude when the body literally begins to die from hypoxia. Similar can be said for hypoxia from other causes. Injury, disease, poisoning, drowning or near drowning etc. Hyperbaric oxygen therapy applies the same physics and physiology to restore oxygenation to deprived tissues to support metabolic function and re-oxygenation of tissue.
Oxygen can be increased in the tissues in one of two ways. By Increasing the fraction of oxygen being breathed, i.e. by breathing oxygen or an enriched air mix. Or, increase the partial pressure of the oxygen being breathed in normal air. Recalling the article on physics, partial pressure and Dalton’s law was discussed along with Henry’s Law. Essentially these two methods achieve the same end. They increase the pressure of oxygen being breathed and an increase of the inward gradient.
At great altitude, even that of high flying jets at 10 000 meters, the oxygen percentage is still 21%. So why the hypoxia, headaches and unconsciousness? Because oxygenation and gas exchange are driven by pressure and not by the percentage or fraction of the gas. By increasing the fraction of the oxygen, you also increase the partial pressure of the oxygen at any given pressure, allowing better gas exchange and oxygen transport to the tissues, including and most importantly the brain. If the percentage is higher, so is the partial pressure at the same pressure. But only to a point. There comes a point where pressure must also be increased to sufficiently increase the inward gradient to overcome hypoxia.
In a medical environment, administration of mask oxygen is called “Baric Oxygen”. It would be of optimum benefit if indeed it could be delivered at a true 100%. This is is rare though considering that standard ward equipment spills more oxygen down your clothes and bed than you actually breathe. Free flow masks simply mix in a bit more oxygen in the air you’re breathing. Most of it is wasted unfortunately, resulting in what could be better outcomes for current practice. The only way to get a true 100% is to use a properly sealing oral nasal mask and a demand valve or hood with free flow pure oxygen.
If climbers have oxygen to breathe that’s fabulous. Breathe it and keep climbing. Because as we state above, the partial pressure of the oxygen when its pure, is higher at the same ambient pressure simply by virtue of the higher fraction. So even at 5000 meters, (+/-16 000 feet, or about half of atmospheric pressure since atmospheric pressure becomes insignificant at 10 000 meters / 33 000 feet), the partial pressure of the oxygen is still high enough to maintain consciousness and avoid ill effects. Breathing air however at 5000 meters would result in a reduced the partial pressure of the oxygen in the air from 0,21 ATA at sea level to about 0.105 ATA at 5000 meters. Not enough to facilitate a significant inward gradient and maintain sufficient oxygen delivery to tissues resulting in hypoxia.
Also covered in the article FLYING AND DIVING – A SOJOURN INTO PHYSICS AND PHYSIOLOGY
The other way to increase the oxygen partial pressure is to descend the climb or activity and go to a place of higher ambient pressure to better facilitate gas exchange and oxygen transport, or make use of a hyperbaric bag, tent, or portable chamber to increase the ambient pressure artificially. This is common place, and hyperbaric bags have been in use for many years. They really are just portable hyperbaric chambers designed to raise the ambient pressure a climber is subjected to, thus alleviating the symptoms of altitude sickness by effectively raising the partial pressure of the oxygen in normal air. Such bags have been extensively used in mountaineering studies, altitude experiments and studies, as well as high altitude aviation and aerospace research as well as high altitude rescue. More info can be found here: http://www.high-altitude-medicine.com/hyperbaric.html
Fabric chambers are discussed under the article DOSAGE: HBOT AND MHBOT
To backtrack to gas exchange briefly and covered in the previous article on flying and diving, I mentioned that when we breathe in, we breathe in 21% oxygen and a portion of it is metabolised, producing the by-product CO2. This is approximately enough to reduce the oxygen content of air we breathe out to about 16%, down from the 21% we breathed in. If we venture into altitudes or areas of low pressure which take that respective partial pressure much below what we can calculate for 16% (0,16 ATA), we risk becoming unconscious and suffering the onset of altitude sickness. as we would if a commercial aircraft cabin were to lose pressure. This is the point at which altitude sickness becomes a concern. Above a partial pressure of 0,16ATA the body functions normally, i.e. we can safely breathe oxygen content as low as 0,16ATA which would equate to 16% oxygen at sea level. The body’s hypoxia response is not triggered above this point. Below this point the hypoxia response is triggered.
This is evident in the widespread use, and global acceptance, of expired air resuscitation (EAR) in life saving and first aid taught in every first aid course available today. A crucial component of CPR. The 16% oxygen we breath out (and into a victim requiring rescue), is enough to sustain normal consciousness, brain function and life. Below this level can be problematic however.
An interesting aside is the use of “intermittent hypoxic therapy and training” to improve sports performance. Practitioners reduce the partial pressure of oxygen in altitude chambers, or better known as vacuum or hypo-baric chambers, to below this key 16% to deliberately trigger the hypoxic response. Sometime as low as the equivalent to 12% oxygen at sea level. this stimulates the development of additional red blood cells which allow the body to transport more oxygen. Rather an extreme way to do it but those red blood cells remain in circulation for some time following training at altitude or in a low pressure, (hypo-baric) chamber. This improves sports performance in the short term using the same physics as hyperbaic oxygen therapy but by triggering the hypoxia response only. HBOT does this as well as providing exponentially more oxygen to tissues. It all ties in with oxygen and how the body responds to higher and lower levels of oxygen. Seemingly a paradoxical statement, the “Hyperoxic, Hypoxic Paradox” will be briefly discussed below.
The Hyperoxic, Hypoxic Paradox:
This really does need it’s own article but very briefly, many folk cite this as a flaw in the theory of hyperbaric treatment. They claim that elevated levels of oxygen prevent the very necessary hypoxia response which triggers the healing and rebuilding processes following injury or disease. When the body suffers an injury, disease or some other cause of lowered localised oxygen (hypoxia), this triggers various genetic responses chief of which is the HIF1a (One Alpha or, Hypoxia Inducible Factor One Alpha response).
The HIF1a gene is a sub unit of the heterodimeric transcription factor hypoxia inducible factor 1 (HIF1), that is encoded by the HIF1a gene. It is considered a master transcriptional regulator of cellular and development response to hypoxia.
In layman’s terms this means that the HIF1a gene is the master regulator for about 60 other genes which are triggered during states of low oxygenation (hypoxia). These states could be as a result of injury, disease or indeed even the natural growth pattern of embryo’s, children and other people still growing. Certain Growth relies on hypoxia response to grow new cells, new vacularisation and tissue.
Many argue that elevated oxygen tension in tissue stops this response, preventing the natural healing responses that the HIF1a triggers. This is the paradox. It doesn’t. It actually triggers it.
Everything is relative, there are no absolute values. if we go to altitude and the relative oxygen concentration drops relative to where we were, and to a significantly low enough point (below 0.16 ATA), the body interprets this as hypoxia and the hypoxia response is triggered. The same can be said for returning to normal oxygen levels from very high oxygen levels in a chamber. The body interprets the relative change as hypoxia even when there is no lack of oxygen. The hypoxia response is triggered releasing stem cells among other repair and rebuild cells. Hyperbaric oxygenation in fact up-regulates the hypoxia inducible factors response which include the vascular endothelial growth factor (VEGF). The one responsible for the growth of new blood vessels. To draw a comparison, when a hypothermic person is exposed to even lukewarm water, it can cause physical burns whereas a person who is at normal temperature will not burn. Its relative to the previous or existing state.
So yes, training at altitude works. The reduced oxygen levels trigger the hypoxia response, and one result is the generation of more red blood cells. Someone who trains at altitude and then competes at normal pressure, is essentially competing in a relative higher pressure or hyper-baric environment in which more oxygen can reach tissue in the same way it does during a treatment. Those living at altitude develop a permanently higher level of red blood cells to the extent of achieving larger than normal spleens, where blood and by extension, red blood cells are stored. It’s how the Sherpa’s don’t need oxygen like the rest of us do.
So, if we consider a climb, or unpressurised flight to 5000 meters, (at 10 000 meters there is almost no pressure and it is considered the top of the atmosphere as far as pressure goes), we experience ambient or barometric pressure at roughly half of 1 Atmosphere absolute (0,5 ATA). So, we can calculate that breathing oxygen at 0,5 ATA is still well above the low end of 0,16 ATA we can tolerate. However, breathing air at this level as calculated above, at 0,105 ATA, is well below that level. Therefore, altitude sickness occurs.
And that’s why simply breathing pure oxygen at high altitude relieves altitude sickness. Because it raises the partial pressure of the gas. Nothing really to do with percentage. Raising the percentage of oxygen being breathed is simply the easiest way of increasing its partial pressure. Although limited by ambient barometric pressure, it is an effective measure on the side of a mountain. The same cannot be said for higher altitudes than this. Extremely high altitudes as experienced in sub orbital flight and the extreme sport “edge of space ballooning” very high altitude flight etc, must make use of pressurised capsules….. also known as hyper-baric chambers. When we as the general public do it, we do it in pressurised cabins in commercial aircraft making an aeroplane a hyperbaric chamber of sorts as well. Even pure oxygen at zero pressure will not enter the body leading to chronic hypoxia. Pressure is key. Hyperbaric physics applied.
Consider then the opposite in a saturation dive to 300 meters of sea water. The ambient pressure at those depths is a massive 31 atmospheres (30 ATA). Even an oxygen percentage, or fraction of gas, of 2% affords the divers a partial pressure of oxygen of 0,6 ATA well above the required minimum of 0,16ATA for healthy physiological function, yet with only 2% oxygen in the mix. Obviously, this couldn’t be breathed at the surface, unconsciousness would be quick and certain. This type of mix is only meant for the “bottom” or “storage depth” mix.
Incidentally, 0.5 ATA to 0.6 ATA partial pressure pf oxygen (ppO2) has historically been a partial pressure range used in space exploration as well. Further establishing pressure as the gas exchange driver, and not percentage (fraction).
The Common Sense Paradox
This begs a question then. In patients who exhibit hypoxic symptoms following accident or illness. Why do medical professionals resist administering higher partial pressures of oxygen to better facilitate gas exchange and oxygen transport? The answer is that it would undermine years of medical teaching and strongly held opinions which echo the sentiments of generations of highly venerated medical instructors and teachers. And this simply isn’t done in medicine. It seems to be a rather sensitive issue. Kind of a “pressure point” so to speak, pun intended. Questioning this leads to many professionals taking this as a personal affront to their competence.
It would also require hospitals to monitor oxygen levels in tissue saturation and not just haemoglobin saturation as they currently do. It’s an sensitive issue with most doctors. They perceive the suggestion that they could do more as an attack on their competency when in fact it’s not. This is not to say that doctors are closed minded to new technology, not at all. In fact, that is one of the governing principals of science is it not? To be open to new developments. Especially low-tech, cost effective modalities such as HBOT. It dumbfounds that governments with limited healthcare funding refuse to see the benefit of improving general well-being in a population thus reducing at least some of the ongoing need for chronic care costs.
The fact remains though that hyperbaric medicine is not included in the standard syllabus for medical students as it stands today. The select committee responsible for deciding just what makes up the syllabus aren’t easy to convince, and unless doctors have covered some diving, altitude or hyperbaric medicine at least at university or post graduate level, it’s likely they’re unaware of the benefits of hyper-oxygenation. Hence it is dismissed out of hand. Accordingly HBOT is labelled complementary therapy and not recognised as a formal medical treatment outside of decompression sickness and atrial gas embolism, which it is commissioned for. Certainly in the UK this is the case. That’s OK though. It means we don’t “qualify” for Care Quality Commission oversight and can operate more easily and deliver this therapy to communities with less bureaucracy.
We envisage a day when there is a hyperbaric chamber in every GP surgery and in every emergency room nation wide.
© Hayden Dunstan