Looking to optimize the atmospheric gas mix and pressure for humans for minimal cellular degeneration

Question

To build another world, I would want a perfected atmosphere that would sustain the air cycle and yet optimize a decreased cellular degeneration. i.e.: increase quality and length of life. Would we want to increase the pressure -- change the mix of the gas mixes or both?

With our earth's atmosphere currently by volume, dry air contains 78.09% nitrogen, 20.95% oxygen, 0.93% argon, 0.039% carbon dioxide, and small amounts of other gases. Pressure on the surface of the earth averages out 1 bar. With Nitrogen being inert and the oxygen ratio enough to promote functional respiratory systems and organ health In humans, how can this be optimized?

Hyperbaric oxygen chambers promote healing, increases cellular oxygen exchange and cellular regeneration. NIH studies show the human body heals faster at a pressure greater than 1 ATA within a mono-chamber of highly concentrated oxygen (more than the human body can breathe through the respiratory system without suffocating). However, this is for short durations of time (1-2 hours) and is not sustainable.

Fick's law of diffusion within the human body -- "The net diffusion rate of a gas across a fluid membrane is proportional to the difference in partial pressure, proportional to the area of the membrane and inversely proportional to the thickness of the membrane. Combined with the diffusion rate determined by Graham's law, this law provides the means for calculating exchange rates of gases across membranes. The total membrane surface area in the lungs (alveoli ) may be on the order of 100 square meters and have a thickness of less than a millionth of a meter, so it is a very effective gas exchange interface." Based on this understanding, we can increase the oxygen concentration rate and breathe it safely if we increase the atmospheric pressure. What is sustainable for long periods of time, is another question?

So, combining the two understandings of the human body, what would be the optimum mix of atmospheric gases and pressure to optimize cellular regeneration with the human body over the lifespan.

1.0 ATA with same gas mix;

1.2 ATA with same gas mix;

1.4 ATA with same gas mix;

1.5 ATA with same gas mix;

higher ATA with same gas mix.

1.0 ATA with 21% O2;

1.2 ATA with 22% O2;

1.4 ATA with 23% O2;

1.5 ATA with 24% O2;

1.5 ATA with 25% O2;

Higher ATA with higher O2?

Answer 1

It doesn't actually matter, hyperbolic oxygen only promotes in the short term even in low quantities because the body adapts to the oxygen level, if high it produces less red blood cells if low it produced more. No matter what the external oxygen concentration (assuming not high or low enough to cause illness) the body's internal oxygen levels will return to normal levels within a few days to weeks. It is exactly the same mechanism we use to adapt to oxygen level differences due to elevation.

Answer 2

You want the lowest oxygen levels tolerable.

Oxygen is very tough on biomolecules. It burns them. Higher amounts of oxygen cause more damage to biomolecules. We need oxygen to burn our food within us but just as having fire in the kitchen runs the risk of burning down the house, having oxygen in the body runs the risk of oxidizing important biomolecules. The current two main causes of mortality in the first world are heart disease and cancer, and both can be linked to some degree to free radical reactive oxygen species.

Thinking on this, I thought that if true one would find low oxygen atmospheres to confer a protective effect - against cancer at least. I was surprised that exactly this has been documented several times, and not just for cancer.

Cancer Mortality in Six Lowest Versus Six Highest Elevation Jurisdictions in the U.S.

The study also compares mortality rates for all causes, heart disease, and diabetes in low versus high elevation jurisdictions in an effort to see if other mortality outcomes are different in low versus high elevations. Statistically significant decreases in mortality, with very large effect sizes, were observed in high land elevation for three of the four outcomes, including cancer.... Another possible explanation, at least in the case of heart disease mortality, is the physiologic responses that accompany higher elevations regarding decreased oxygen levels.

The author of the linked paper thought that increased ambient radiation (radiation hormeisis) was part of the protective effect of altitude which is a legitimate theory though one I find somewhat implausible. Less free radical damage in the presence of less oxygen I find much more plausible.

Of course % O2 is the same at all altitudes but at higher atmospheric pressure there is a lower absolute amount of all gas molecules, including oxygen.

One can see the different effective O2 concentrations at different altitudes here: https://www.higherpeak.com/altitudechart.html

The difference in effective O2 between the altitudes studies in the linked study is not that great - maybe 3%. Even Boston vs Pikes Peak is 20% vs 12%. It is remarkable that these sort of differences are associated with significantly different mortality rates. Noted: association is not causality.

Given a choice of environments I think a normal atmospheric pressure and lower content of O2 would be easier on humans than a low atmospheric pressure and normal 20% O2. This chiefly because low atmopheric pressure = low water vapor pressure and dehydration happens more easily.

The less oxygen, the less risk for damage. Humans live and thrive in Bolivia at 17000 feet+ https://www.nytimes.com/2015/03/11/sports/soccer/at-home-in-thin-air-bolivian-soccer-clubs-play-over-their-head.html which is only 11% O2 - though it is difficult for visitors unaccustomed to the low O2 level there to do well. Humans can adapt to low oxygen, which to me seems like adapting to limitations on the fire you use for cooking: you need to pay attention and plan more for the cooking but it is safer for all involved.