Geezer Gas

[hroark2112]

Oxygen levels only affect your breathing when the blood oxygen level is low. Breathing rate even on 100% oxygen is whatever your normal breathing rate would be on air, unless you intentionally lower your respiration rate.

Last summer I took 2 chamber rides for a total of 12 hours. My respiration rate was unaffected by breathing pure oxygen, whether we were pressurized or at sea level. I've seen the charts, and awake or dozing, whatever the pressure, the only time my respiration rate was noticeably impacted was when I dozed off and they woke me up for an air break.

 

[Akimbo]

Oxygen levels only affect your breathing when the blood oxygen level is low. Breathing rate even on 100% oxygen is whatever your normal breathing rate would be on air, unless you intentionally lower your respiration rate...

I have very little experience with low blood O2 but my understanding is the breathing rate is primarily controlled by CO2, except for those induced by anxiety. The blood O2 is typically elevated even on air at elevated pressures/depths. Am I missing something?

 

[hroark2112]

I have very little experience with low blood O2 but my understanding is the breathing rate is primarily controlled by CO2, except for those induced by anxiety. The blood O2 is typically elevated even on air at elevated pressures/depths. Am I missing something?

If your blood O2 gets too low, respiration is increased to attempt to raise it.

Just a little nugget I found during some research

 

[Akimbo]

If your blood O2 gets too low, respiration is increased to attempt to raise it…

Then wouldn’t breathing a hypoxic Oxygen mix cause increased respiration? From what I have observed, as long as CO2 is ventilated out of the lungs normally the person’s respirations stay in the normal range until they start to lose consciousness, ultimately passing out and expiring if uncorrected. Is there something different about clinical settings?

It gets very interesting when inadvertently breathing a near-hypoxic mix like 1% O2 on the surface. People pass out almost instantly, usually before completing a full inhalation cycle. It used to happen far too often in the early days of saturation diving. It happened to me once, I have seen it twice, and heard about it at least 20 times. Procedures are better now and most chambers are fitted with Oxygen analyzers you can see before entering.

 

[hroark2112]

Here's one of the articles I found on it:

Factors That Affect Respiration Rate | LIVESTRONG.COM

 

[Akimbo]

That is consistent with my understanding (color added for emphasis):

The amount of carbon dioxide in the blood is a primary influence on respiratory rate. As your activity level increases, your cells--especially muscles cells--produce increased amounts of carbon dioxide. The rhythmicity center in the brainstem detects increased carbon dioxide and increases the respiratory rate to eliminate the excess.
<snip>
Blood oxygen content is a secondary influence on respiratory rate. Normally, the blood oxygen level is 80 to 100 millimeters of Hg. Respiratory rate is stimulated if it drops below 50. A blood oxygen level below 50 is extremely low, which is why this respiratory control is of secondary importance compared with other controls.

It is hard to imagine how the blood Oxygen level could drop that low in a hyperbaric environment while CO2 is being ventilated normally. Barotrauma perhaps?

I wonder why that doesn't kick-in with hypoxic mixes?

 

[Saltyhawg]

The one exception to CO2 driving respiration is in people with chronic CO2 retention (severe COPD). In those people the chronically elevated CO2 extinguishes its effect on respiration. O2 then becomes the driver and giving one of these people high levels of supplemental O2 can suppress respiration to the point of death. 'Course those folks shouldn't be diving anyway.

Supplemental O2 to a trained athelete with a 99% O2 saturation on room air is pointless. Placebo effect only.

In 30 years of practice I've only seen O2 saturations under 50% a handful of times and always in a code blue situation......all ended in death (usually from massive pulmonary embolism)

 

[Octopusprime]

Well I am going to leave this discussion up to the medical professionals using evidence based practices.

but I will ask one question... If breathing higher levels o2 like nitrox or full o2 does not change the gas makeup of the blood why do they use 50% nitrox and 100% o2 for deco diving ? Dive tables and deco algorithms have come from decades of research and evidence.

 

[MaxBottomtime]

It's not the increase in O2 that speeds decompression, it is the omission of nitrogen. Our bodies only use about 6% of the O2 we breathe and exhale the rest. Increasing the O2 doesn't give us any more. You could replace the nitrogen with any breathable gas, but O2 is a lot cheaper than helium.

 

[Akimbo]

... If breathing higher levels o2 like nitrox or full o2 does not change the gas makeup of the blood why do they use 50% nitrox and 100% o2 for deco diving ?...

Because it creates a higher partial pressure difference across the alveoli in the lungs which allows diluent gases like Nitrogen and/or Helium to transfer out of the blood faster.