1) Dramatic changes in glucose
and insulin in the blood (
diabetes) that displace oxygen.
2) Side effects from drugs, such as those for cholesterol, blood pressure and arthritis that change the metabolism of the nerves thus altering the way they use oxygen. (ex: Pravachol Amytriptyline)
3) Exposure to toxic compoundss that makes oxygen unusable. Especially solvents (ex: benzene, 1 1 1-Trichloroethane, M.T.B.E, chlorine, etc.) and metals (lead, arsenic, mercury, cadnium, etc.