Asphyxia due to oxygen deficiency by gaseous substances

The determination of the cause of death in asphyxiation gas cases is very difficult because of the variation in circumstances surrounding such deaths. To clarify the cause of death and to identify the factors involved in asphyxia, the symptoms during asphyxia, the concentration of gases at the respiratory arrest, the time to death and the concentration of the gaseous substances in the tissues were studied using rats and six gases. Three inhalations were used: (1) rapid asphyxia (2-3 min) in the exposure chamber in which the oxygen was depleted completely, (2) prolonged asphyxia (20-25 min) by gradually depleted oxygen, and (3) asphyxia by the inhalation of gases saturated with a critical gas concentration, maintaining the O2 at 20% (60 min). In the rapid asphyxia groups, respiratory arrest occurred within 30 to 40 s, followed by cardiac arrest 2 or 3 min thereafter. Severe convulsions were observed only with the use of nitrogen. In the prolonged asphyxia groups, respiratory arrest occurred at the concentration of 4-5% O2 with non-toxic gases (N2, CH4, N2O, and propane). The toxic gases CO2 and Freon-22 produced respiratory arrest at the concentration of 6.6-8.0% O2 (60-67% CO2) and 13-14% of O2 (30-35% Freon-22), respectively. Variations in the concentrations of the gases among the tissues was observed according to the type of asphyxia, type of gas and the duration of exposure. The concentration of the fat-soluble gases in the adipose tissue showed marked variation according to the duration of the exposure. The distribution pattern of methane was different from those of the other gases, in which the variation of concentrations among the tissues except lung were little in both rapid and prolonged asphyxia. These phenomena were considered to be attributable to the solubility of the gaseous substances in blood and tissues. Atrophy in the alveoli was observed after the rapid asphyxia with CO2 and N2O. Local hemorrhaging in the lungs was also observed, especially in CO2 asphyxia. The risks of oxygen-depletion asphyxia are the rapid reaction of loss of consciousness and respiratory and cardiac arrest. This paper presents valuable findings for the diagnosis of the cause of death and estimating the situation of the accident in cases of asphyxia.