Carbon dioxide causes respiratory poisoning
(1) Low concentration of carbon dioxide can excite the respiratory center and accelerate the breathing. High concentration of carbon dioxide can inhibit and paralyze the respiratory center
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(2) Since the diffusion capacity of carbon dioxide is 25 times stronger than that of oxygen, carbon dioxide is easily diffused from the alveoli to the blood to cause respiratory acidosis.

It is rare to see simple carbon dioxide poisoning in the clinic. As carbon dioxide in the air increases, it is often accompanied by a decrease in oxygen concentration.
For example, vegetables and fruits stored in the cellar produce carbon dioxide when they breathe, and consume oxygen. Unprotected measures of poisoning into the mantle are caused by high concentrations of carbon dioxide and oxygen deficiency. The test proves that the concentration of carbon dioxide in the air with sufficient oxygen is not harmful to humans; however, if the oxygen concentration is less than 17%, the air contains 4% carbon dioxide, which can cause human poisoning. Hypoxia can cause pulmonary edema, cerebral edema, metabolic acidosis, electrolyte imbalance, shock, hypoxic encephalopathy, and the like.
If you are locked up in a completely sealed room, you will die first from carbon dioxide poisoning without first dying from hypoxia.