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I am doing my PPL course in the Czech Republic and here they have the following question in tests: when during a day is the resistance of a human organism to hypoxia the best? There are 3 possible answers:

  • 3 am
  • 12 am
  • 5 pm

What is the correct answer and why? Is a human's ability to resist hypoxia connected somehow with the time of day? FAA book doesn't have a word about it.

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    $\begingroup$ If it's on the test, it stands to reason that it's in the study material you're expected to use, because that study material would be adapted to the test you'll be taking. What do your Czech books say on the matter? $\endgroup$ – a CVn Feb 11 at 8:52
  • $\begingroup$ @CVn couldn't find anything for now. I prefer the FAA book because it's generally much more detailed and better written than the local books. $\endgroup$ – Kirill Metrik Feb 11 at 17:06
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    $\begingroup$ Hmmm. In my experience, tests aren't designed to facts in general. They are designed to a specific curriculum, and that will most closely match the books they assigned. For instance, your course may make certain assumptions, e.g. European VFR operation, which the test questions will also assume. If you create a more general answer, it may not match the course. Thus, you can get burned by a "bad" test. $\endgroup$ – Harper Feb 11 at 22:59
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    $\begingroup$ Mildly reduced oxygen saturation can impair night vision without causing other noticeable symptoms. The FAA PHAK mentions this in chapter 17. Maybe this is what the test author was trying to get at with their poorly-worded question. $\endgroup$ – pericynthion Feb 12 at 0:25
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    $\begingroup$ I have not found a reference to answer this question other than a study of hypoxia resistance in rats at different times of the day. In Russian. $\endgroup$ – Juan Jimenez Feb 13 at 15:00
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I'd say the resistance to hypoxia changing with hour may depend on things such as Hemoglobin dissociation curve, glucose blood levels, levels of other hormones, and overall metabolic rate. I'd look for an answer in medical sites, physiology textbooks, and EntrezPubMed. Good luck! Salut +

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It depends upon what you mean by hypoxia resistance. Keep in mind you may have to take into account hypoxia’s effects on various organs and organ systems of the body and the effects their impairment at different hours. I’m not going to give away an answer for a test, but that is an additional clue for you to go on. Good luck.

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  • $\begingroup$ I've checked with the answers and the correct answer is 3am. Still have no idea why... $\endgroup$ – Kirill Metrik 5 hours ago
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Half of the challenge behind piloting exams is understanding what the question is asking. I think this is one example of many poorly-worded questions. AFAIK hypoxia doesn't care what time of day it is, it's all about absorbing oxygen. However, some of the symptoms of hypoxia include reduced colour and night vision, which is bad news for night flight.

If the question doesn't make sense, look at the answers for clues. Out of the 3 options here, 2 of them are very similar - times where it is nighttime year round, and one where it is daylight (varying with latitude and season of course).

So the exam is asking you to choose between day and night, essentially. The symptoms of hypoxia are more abundant at night, so I think you have your answer there.

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