Nighttime oxygen requirements

A

azaviator08

New Member
I have found this in a couple of books but it is hard to find a straight answer in any of the FAA books.

Why do we need more oxygen at night at lower altitudes?

Is it because of the fact that the eyes have to work harder so they are essentially taking up more oxygen. Also the whole body itself is working harder because you are used to sleeping at night so you may be fatigue, so the body itself requires more oxygen b/c of this.
 
azaviator08 said:
I have found this in a couple of books but it is hard to find a straight answer in any of the FAA books.

Why do we need more oxygen at night at lower altitudes?
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Because hypoxia causes tunnel vision, and you see better away from the center of your eyes at night. The whole "rods/cones" thing as I understand it.
 
azaviator08 said:
I have found this in a couple of books but it is hard to find a straight answer in any of the FAA books.

Why do we need more oxygen at night at lower altitudes?

Is it because of the fact that the eyes have to work harder so they are essentially taking up more oxygen. Also the whole body itself is working harder because you are used to sleeping at night so you may be fatigue, so the body itself requires more oxygen b/c of this.
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It's a recommendation not a requirement.

That said, human eyes are obviously better suited to day vision than night vision. The focal point of the eye, the fovea, has a much larger concentration of cones (used to sense brightness and color) than it does rods (dull colors and darkness), which are more concentrated around the periphery of the fovea. The eyes aren't necessarily working harder at night, they are just less efficient at night than during the day when you are experiencing even mild forms of hypoxia.

The American Optometric Association has a interesting article about it here

http://www.aoa.org/x5352.xml
 
Partial Pressure is not different night or day. "Human vision and the night sky" by Michael Borgia, explains the at eyes are oxygen hungry organs and the first part of the eye affected by hypoxia is the rod cells of the retina.

Thus the lower altitude recommendation at night.
 
richarms said:
Partial Pressure is not different night or day. "Human vision and the night sky" by Michael Borgia, explains the at eyes are oxygen hungry organs and the first part of the eye affected by hypoxia is the rod cells of the retina.

Thus the lower altitude recommendation at night.
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Is he a doctor of some sort?

-mini
 
Mini,

Nah, he's an astronomer. The book's about improving night vision. Just a single source.
 
richarms said:
Mini, what do you mean?
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Is the author a doctor that his information is credible or is he just writing a book? I could write a book about lots of things...doesn't mean the information is credible.

Before I go look for it to buy and read I was just wondering if he's some kind of doctor that would have credible information. That's all.

-mini
 
minitour said:
Is the author a doctor that his information is credible or is he just writing a book? I could write a book about lots of things...doesn't mean the information is credible.

Before I go look for it to buy and read I was just wondering if he's some kind of doctor that would have credible information. That's all.

-mini
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Good point. I still believe the day/night partial pressure is the same. The eye's the problem. I'll look for a better reference than a book I was reading.
 
While I wasn't trying to recommend the book (haven't finished), here is some info on the author:

Michael Borgia is a jet pilot instructor for Flight Safety International, and in his spare time a member of Delmarva Stargazers Astronomy Club. He has been an amateur astronomer for 30 years – since his childhood. He believes that he has been in every situation, asked every relevant and irrelevant question, and experienced every frustration known to amateur astronomy. He is the author of numerous training documents for Flight Safety and American Flyers, including full-length technical training texts.
 
richarms said:
Mini,

Nah, he's an astronomer. The book's about improving night vision. Just a single source.
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Beyond all the other scientific literature already out there on this subject, I'd be willing to listen to an astronomer on the issue as well. I bet they know a thing or two about viewing objects at night.
 
richarms said:
While I wasn't trying to recommend the book (haven't finished), here is some info on the author:

Michael Borgia is a jet pilot instructor for Flight Safety International, and in his spare time a member of Delmarva Stargazers Astronomy Club. He has been an amateur astronomer for 30 years – since his childhood.
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Interesting.

richarms said:
Good point. I still believe the day/night partial pressure is the same. The eye's the problem. I'll look for a better reference than a book I was reading.
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I'm not saying that's wrong, but I'd rather hear it from a doctor than a pilot/instructor/astronomer. There are, after all, still instructors that think you can blow up a Piston engine if you fart in it's presence.

He believes that he has been in every situation, asked every relevant and irrelevant question, and experienced every frustration known to amateur astronomy.
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Why was I not surprised to read that? :rotfl:

-mini
 
Rods need approximately twice the amount of oxygen as cones, making one more susceptible to hypoxia symptoms with regards to the eyes at night versus day. I will grab a source later and post it but it is various medical books if you have access to any you will quickly find the answer.
 
Eye Blood Flow
Photoreceptors constitute the cells with the highest rate of oxidative metabolism in the body. As the outer retina (the photoreceptor layer) is avascular, the oxygen is provided by the high blood flow from the underlying choroid. Since this blood flow is not regulated by oxygen consumption, primary rod (97% of all photoreceptors in the mouse retina) degeneration leads to a huge increase in oxygen [27,28].
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Avascular means without blood vessels. Basically this points out that rods/cones use a large amount of oxygen, as already stated. With 97 percent being rods, it is obvious that at night, 97 percent of the eye must be supplied with oxygen where as during the day only 3 percent.

Source: http://www.biomedcentral.com/1471-2199/8/74


Oxygen Distribution (Retina)
This clearly indicates that oxygen consumption decreases in light adaptation, as has been reported for other vertebrates.
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The maximum (ie, dark-adapted) oxygen consumption of the outer half of the parafoveal primate retina appears to be approximately 75% of the oxygen consumption of the cat area centralis; however, because we have data from only two monkeys, this value must be considered somewhat preliminary.
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Despite some differences, it appears that the cat retina provides a relatively good model for
oxygen distribution and consumption in the parafoveal retina of primates and, presumably, humans.
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As can be seen, the required amount of oxygen for night versus day is vastly different. Granted, these are not human and studies of the human retina, from my research, are not common, in fact, I couldn't find any.

Source: http://www.iovs.org/cgi/reprint/34/3/516.pdf



***Change to Original Definition***

From my past knowledge, I was under the impression that a single rod used more oxygen than a single cone. After this research it appears it is more likely that they are even, if anything, rods need less oxygen per single rod versus the individual cone. However, due to the vast quantity of rods over cones, the oxygen requirements to utilize all rods (for night flying) versus using all cones (for day flying) is approximately twice as much.



Additional Information
One last source, which I found to have some interesting information in this area: http://www.ncbi.nlm.nih.gov/pubmed/11173251
 
That was actually a question on my CFI checkride. Its exactly what SHDW said. It's in one of the FAA books also that the eyes have 10,000 more rods than cones, therefore more to be fed with oxygen. That is the simple answer that worked for my checkride, If I run across the page I got that from I'll let you know (I would guess its in the PHAK). I also saw a similar statement in a Flight Physiology book for a class I was taking.
 
29.92inHg said:
the eyes have 10,000 more rods than cones
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Right, but the numbers are off, he likely didn't care or didn't know though. Here:

The rods are more numerous, some 120 million, and are more sensitive than the cones. However, they are not sensitive to color. The 6 to 7 million cones provide the eye's color sensitivity and they are much more concentrated in the central yellow spot known as the macula
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Rods = 120 million
Cones = 6-7 million sub-divided into:
"red" cones (64%), "green" cones (32%), and "blue" cones (2%) based on measured response curves.
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Source: http://hyperphysics.phy-astr.gsu.edu/hbase/vision/rodcone.html

It is what I used in my night seminar and ground school.
 
bdhill1979 said:
According to those recommendations I should be wearing a cannula in my house.
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Perhaps only at night lol :laff:

I used to wear the cannula in the Caravan all the time at night on long flights. It was fun with pax/ or "co-pilots" when they weren't wearing the Oxygen mask at 13,000' or so. It's quite a transformation in your night vision once you put the mask on.
 
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