Flying @ night, altitude, smoking and O2

[Squawk7777]

Hello!

I came across some med questions and can’t find the answer because I misplaced my areomedical books.

At night it is recommended that the pilot wears oxygen if he is flying unpressurized at an altitude of 5000 feet or above. From what I remember from ground school, the cones [or rods – always mixed those up :rolleyes: ] use more oxygen at night. Question is why? Why does the pilot need more oxygen at night at the same altitude than during the daylight?

Next question is about smokers. Why exactly do they need oxygen at a lower altitude than a non-smoker? What exactly happens in the lungs?

7 7 7 7

[redsnail]

Your eyes don't use more O2 at night. What the deal is, the cells used for colour are the cones (think cones for colour) have a higher O2 demand than the rods. It doesn't matter if it's day or night. At night it's dark so now the rods come into play. If you're at altitude (+8000' it starts being noticeable for a non smoker) O2 can help whether it be day or night. Hence the requirement for O2 above 10,000'. (In many countries)
Smokers are at a disadvantage. Carbon monoxide is the principle culprit here. As you know haemoglobin carries oxygen around the body in the blood. Carbon monoxide has a much greater afffinity for haemoglobin (something in the vicinity of at least 200x). That is, haemoglobin will favour picking up CO over oxygen. Since you're at altitude, there's less O2 for us to breathe, a smoker has less O2 than a non smoker because of the effects of CO. Even if you're not smoking at the time, the effects do last.

[the wizard of auz]

I think the factor you might be looking for is the atmospheric changes that happen when we change from day to night flying.
due to these atmospheric changes, there is even less o2 to be had at lower altitudes at night than during the day.
I personaly do notice the differance between 9500ft during the day and 9500 at night. not a problem as such, but noticable.
it makes your cigerette harder to smoke at night time. ;)

[camber]

Wizard are you under some sort of spell, or are you serious?

[the wizard of auz]

I'm serious...........Really

[Northern Chique]

Hey Wiz! what are you doing here? :D and what you doing flying that high anyways .... aint no cows up there! :))

Apparently the teaching is carbon monoxide has 100 times the affinity for haemoglobin than oxygen... still means youre screwed either way, and serious cases have been sent to hyperbaric for intensive treatment in the past. Nasty nasty stuff!

Cigarette smokers also have a problem in they scar lung tissue over a period of time, thus reducing the amount of usable cells to transfer Oxygen and carbondioxide at cell level in the lungs. (Alvioli) They have annectdotal evidence of smoking pilots faring better on less oxygen over a sustained period as their bodys have already learned to sustain function at a lower level of oxygen. They however will succumb to hypoxia at a great rate once decompensation levels are reached. By comparison, non smokers fair much better than their smoking counterparts.

The difference overall is thought to be a smokers Oxygen content would be that a nonsmoking person would have at 5 1/5 to 6 thousand feet asl. The change in available Oxygen as partial pressure decreases makes it more difficult to obtain adequate levels. As altitude further increases, partial pressure continues to decrease to a point where very little Oxygen transferance is taking place. Thus hypoxia (absence of available oxygen to the body) takes effect. The first instance this may be noted is affected night vision.

Night vision is impared by a number of factors, and Wiz is right on the money insofar as atmospheric changes occur, but the same changes are noticable with increased density altitude on a stinkin' hot day are they not? (or "oh hell Im back to the met books!")...

Its kinda cool getting onto a portable SPO2 monitor to see what happens to heart rate and Oxygen levels on the blood through various altitudes and conditions, as well as hypoxia affecting vision and decision making processes. I tell you, the lights get pretty dammed blurry after a bit.

[slim_slag]

Night vision is impared by a number of factors, and Wiz is right on the money insofar as atmospheric changes occur, but the same changes are noticable with increased density altitude on a stinkin' hot day are they not? (or "oh hell Im back to the met books!")...

Nope, atmospheric temperature changes don't really affect your lungs. You can safely assume the air in your alveoli is at 36.9C and 100% saturated at any place you might realistically find yourself at.

Auz, what's that you been smoking?

[the wizard of auz]

Do some study dude!!!.
I'll give you a small hint. do you remember when you were doing met?. Do you also remember when you were told about why radio nav aid range changes at night?.
or why radio wave propegation is better at night?.
I'll give you another hint...........Ionesphere lowering.
there ya go dude, have a number and do some pondering. ;)

I wasn't going to bite, but I just couldnt help meself. :}

[palgia]

Not sure if you guys are serious or just kidding around. (Maybe I don't get the joke)

But just to make sure nobody gets confused or learns anything incorrectly, I just want to clarify a few things.

As a meteorologist, I can assure you that there is NO difference between day or night, as far as partial pressure of oxygen at a given altitude.

Think about it. When you are flying at say, 9,500 ft, what you are actually flying is a given pressure level. The pressure depends on what setting you have on the Kollsman window of your altimeter. In the case of a standard atmosphere, at 9,500 ft with 29.92 set on the altimeter (or 1013) you will be flying at a pressure level of about 710 hPa. This will not change regardless of time of day, or day of the year.
Since we are talking about altitudes in the heterosphere (the part of the atmosphere with near-constant gas composition), 21% of the atmospheric pressure will be exerted by Oxygen. In the case of a standard atmostphere at 9.500 ft, this would be about 150 hPa. This is what determines how much oxygen you breathe: the partial pressure of oxygen.
How much of this pressure actually gets diffused into the blood, transported to the tissues and utilized in respiration, depends on many other factors.

Bottom line is that the amount of partial pressure depends only on atmospheric pressure. It would be true to say that flying at 9.500 ft from an area of surface high pressure to an area of surface low pressure (assuming you are updating the alt setting) would reduce the partial pressure of oxygen, but this difference would be difficult to notice.



The "ionosphere lowering" has nothing to do with this phenomena.
In fact, as far I was taught, the ionosphere does not lower (except for the upper part) at night. If it did lower, we would have a DECREASE in radio range. Instead, the bottom of the ionosphere shifts to a higher altitude.
This is because the ionosphere itself is nothing more than charged ions created daily by the dissociation of ozone into oxygen caused by the UV rays. During the day, UV rays "thicken" the ionosphere. At night, when there is virtually no UV radiation, the oxygen atoms and molecules re-combine back together to form ozone. Because the rate at which this process occurs depends on the local atmospheric pressure, the lower part of the ionosphere will disappear more rapidly than the upper part of the ionosphere. (lower altitude = higher pressure = faster rate) Therefore this means the average height (midpoint) of the ionosphere is raised to a higher altitude, allowing for increased radio wave propagation range. (different frequency of radio waves bounce off at different altitudes, but I think its safe to assume that most do so in the lower part of the ionosphere)

Back to the original question, I was not aware that the rods needed more O2 than the cones.
I was taught that the amount of vision degradation due to hypoxia was the same, day or night (at a given altitude, or rather pressure level:8). However, since both visual acuity and color vision are normally a lot worse at night than during daylight (even at sea level), the degradation due to hypoxia becomes significant at night at a lower altitude. Any AMEs out there, please correct me if I am wrong.

Squawk 777,

an easy way to remember which one is which as far as rods/cones and day/night is to memorize that
Pilots use their rods at night... :}

[redsnail]

Palgia,
Doh, fair cop mate. I guess I meant to say that cones are more light dependant to operate. That is, they need light and plenty of it to see the nice colours. Rods on the other hand aren't used for colour perception, more peripheral vision. Since there's plenty of light during the day, the degradation in vision isn't as obvious as it is at night (and at altitude).

[the wizard of auz]

I hate it when sensible people come on and ruin a good wind up.
I could almost hear pages being turned and books being thumped around in a research flurry.
Oh well, I got a couple of bites. I was going to drag iyt out for a bit longer with some more scientific baffle.
Good pick up on the direction the Ionsphere travels at night. ;)

It was fun for a little while. :} ;)