The course of respiration and circulation in death by carbon dioxide poisoning.

To investigate the effects of very high concentrations of carbon dioxide (CO2) upon the course of respiration and circulation, dogs were allowed to breathe high concentrations of CO2 while intrathoracic pressure, blood pressure (BP) in the femoral artery, electrocardiogram and electroencephalogram readings were registered. The respiratory movements either increased just after inhalation of high concentrations of CO2 and then ceased in 1 min, or decreased and continued for a while according to the concentrations of CO2. The BP showed an initial depression, then returned to the original level, then fell again rapidly or maintained an appreciable level for a while until circulatory breakdown. In the dogs allowed to breathe the gas mixture of 80% CO2 with 20% O2, the respiratory movement ceased in 1 min, and the terminal respirations were seen with the circulatory breakdown after apnoea of several minutes. These findings showed that the cause of death in breathing high concentrations of CO2 is not hypoxia, but the CO2 poisoning.