[Potentiation of carbon dioxide for hypoxic hypoxia-induced death]

The circumstances in the hypoxic death cases are generally classified into pure hypoxic condition as replacement of O2 gas with N2 gas and hypercapnic hypoxic condition as replacement of O2 gas with CO2 gas. Although pure hypoxia and hypercapnic hypoxia should be distinguished, there are very few reports and data on their distinctive research. In order to evaluate the toxicity of both hypoxic gases in male mice, we determined the interaction range of O2 and CO2 gas concentrations, measured the spontaneous motility of mice exposed to various gases and investigated the effect CO2 gas on the hypoxic hypoxia-induced death. Gas toxicity was evaluated by the median lethal concentration (LC50) of O2 during 10 minutes' exposure to the gases, using a self-made simple experimental apparatus for acute inhalation gas toxicity. The LC50 of pure (nitrogen-replacement) hypoxic gas was 6.0% (95% Conf. L., 5.6-6.4%) in O2 and the LC50 of hypercapnic (CO2 gas-replacement) hypoxic gas was 8.8% (7.4-10.1%) which was significantly different (p less than 0.05) from that of pure hypoxic gas. From the result described above it is suggested that CO2 potentiates the hypoxic hypoxia-induced death. The potentiation of CO2 occurred in the range of 6 to 12% of O2 concentration. While there was no dead case in the normoxic gas (O2 not equal to 21.0%) even of which nitrogen was replaced with CO2 gas by 14.9%. Not only significant difference of the lethal O2 gas concentrations, but also a little differences of signs and symptoms were observed between pure hypoxia and hypercapnic hypoxia.(ABSTRACT TRUNCATED AT 250 WORDS)