QUOTE(GolfrGuy7 @ Feb 6 2012, 07:46 PM)
Hey guys. I'm working on my CFI right now and ran into something that I hadn't heard of. In one of my Gleim books it says that the body is more susceptible to hypoxia at night. I understand that the effects of hypoxia are usually more prevalent at night (especially deterioration of vision), but I do not understand why our bodies would be more susceptible to becoming hypoxic at night.
The only thing reason I could come up with is that fatigue might be a factor. But then again, everyone is on different sleep cycles, so some people may be less fatigued at night than they are in the day.
Anyone care to enlighten me?
I do not think hypoxia is any more prevalent at night, just its effect on vision.
The effect of altitudinal hypoxia on night vision is primarily one of an elevation of the rod and cone threshold. Although decreased cone function is clearly demonstrated by the loss of color vision at hypoxic altitudes, the decrement in central VA is usually insignificant. However, scotopic night vision at altitude can be significantly reduced. Scotopic vision has been reported to decrease by 5% at 3,500 feet, 20% at 10,000 feet, and 35% at 13,000 feet, if supplemental oxygen is not provided. Thus, the use of oxygen, even at low pressure altitudes, can be very important at night.Good reading
on the subject.