Query re: Partial pressures of O2 in high vs low pressure environments

In summary, the partial pressure of oxygen (O2) is significantly higher in high pressure environments compared to low pressure environments. This is due to the fact that the total number of gas molecules in a given volume is greater in high pressure environments, resulting in a higher concentration of O2 molecules. This can have significant impacts on physiological processes, as the body must adjust to the varying levels of O2 in different environments. Additionally, high pressure environments can lead to increased levels of dissolved O2 in liquids, such as blood, which can also affect the body's functioning. Overall, understanding the differences in partial pressures of O2 in high and low pressure environments is important for understanding the effects of these environments on both living organisms and industrial processes.
  • #1
Thunderhoof
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TL;DR Summary
Why are people climbing Everest on 100% oxygen hypoxic?
Hi, I'm currently learning to scuba dive and we use a very simple way to calculate the partial pressure of oxygen at depth to avoid oxygen toxicity, for example at sea level of 1 atm and 21% O2 concentration the partial pressure is calculated to be 0.21, and at 60m (pressure increases by 1 atm for every 10m of depth) that's 7 atm x 21% which is 1.47 which is around the cut off point for O2 toxicity, at which point we start needing to breathe hypoxic gas mixtures to maintain a safe partial pressure of oxygen. For reference the world record dive of 534m was achieved with the diver breathing a mixture of 49% hydrogen, 50.2% helium and 0.8% oxygen to maintain a safe partial pressure of oxygen.

If this is the case for high pressure environments why does the same not seem to hold true for low pressure environments like the top of Everest? If the partial pressure of 100% oxygen at 1 atm is equal to 1.0, why is the partial pressure of 100% oxygen at the 0.35 atm on Everest not equal to 0.35 and is instead hypoxic? I'd appreciate any insight on this.
 
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  • #2
The partial pressure of 100% oxygen at 0.35 atm is 0.35 atm. Why do you think it is hypoxic?
 
  • #3
There seem to be a significant number of reports of hypoxia from people climbing Everest on 100% oxygen, but I suppose this could be because of a limited flow rate I suppose compared to the full flow rate used in diving, or perhaps other physiological issues resulting from the low pressure atmosphere.
 
  • #4
Could you link to these reports?
I don't know but suppose they don't use regulators like in SCUBA to equalize pressure of the flowing gas to ambient pressure. Perhaps, a manual flow control instead. (?)
 
  • #5
Reading this article seems to explain the hypoxia.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1114067/

"However, it is difficult and expensive to arrange oxygen supplies so flow rates are kept low. The oxygen is used when sleeping, normally at 1-2 l/min via a face mask, and when climbing above 8000 m, normally 2-3 l/min."

Compared to 15-20 l/min when diving a climber would be getting substantially less oxygen into their body even at 100% vs 20%.
 

FAQ: Query re: Partial pressures of O2 in high vs low pressure environments

What is partial pressure of O2 and how is it different from total pressure?

Partial pressure of O2 refers to the pressure that oxygen alone contributes to the total pressure of a gas mixture. It is different from the total pressure, which is the sum of the partial pressures of all gases present in the mixture. For example, in air, the total pressure is the sum of the partial pressures of nitrogen, oxygen, carbon dioxide, and other trace gases.

How does partial pressure of O2 change in high pressure environments?

In high pressure environments, the partial pressure of O2 increases proportionally with the total pressure, assuming the fraction of oxygen in the gas mixture remains constant. For example, if the total pressure doubles, the partial pressure of O2 will also double, provided the oxygen concentration is unchanged.

Why is partial pressure of O2 important for human physiology?

Partial pressure of O2 is crucial for human physiology because it determines the amount of oxygen available for diffusion into the bloodstream and subsequently to tissues and organs. Adequate partial pressure is necessary to maintain cellular respiration and metabolic processes. Both low and excessively high partial pressures can lead to health issues such as hypoxia or oxygen toxicity, respectively.

How does partial pressure of O2 affect breathing in low pressure environments like high altitudes?

In low pressure environments, such as high altitudes, the partial pressure of O2 decreases because the total atmospheric pressure is lower. This reduction in partial pressure can lead to hypoxia, a condition where insufficient oxygen reaches the tissues. The body may respond by increasing breathing rate and producing more red blood cells to compensate for the lower oxygen availability.

What are the potential risks of high partial pressures of O2 in hyperbaric conditions?

High partial pressures of O2 in hyperbaric conditions can lead to oxygen toxicity, which can cause symptoms such as visual and hearing disturbances, muscle twitching, seizures, and lung damage. This is because excessive oxygen can produce reactive oxygen species that damage cell membranes, proteins, and DNA. Hyperbaric oxygen therapy must be carefully monitored to avoid these risks.

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