EFFECT OF HIGH CARBON DIOXIDE CONCENTRATION ON MENTAL PERFORMANCE AND SOME SENSORY FUNCTIONS

抄録

The present authors investigated the effect of CO₂ on human mental performance, critical fusion frequency of flicker, and hearing. In view of the results obtained, we conclude as follows:
1. The critical concentration of CO₂ to maintain the above stated functions almost unaltered for a long period is safely regarded as 4%. But 5% CO₂ shows practically no appreciable effect upon them for 2-3 hours. Subjective complaints due to the CO2 inhalation also appear above 5%.
2. This critical concentration coincides with that, in which steep rise of alveolar pCO₂ and remarkable respiratory acidosis begin to occur, and functions under bulbar or hypothalamic control (respiration, heart rate, vasomotor or sweating response) start with acceleration. It seems allowable, therefore, to ascribe the narcotic action of CO₂ to its effects exerted on nervous elements in general such as investigated by Lorente de Nó, and to be either narcotic for cortical centres or excitatory for subcortical ones, corresponding to their respective characteristics in formation of synaptic circuit.
3. Above 6%, its narcotic effect on mental performance or sensory functions and subjective symptoms become distinct. Concerning the mode of its action, Clark's formulation seems applicable for the effect-concentration relationship and an expression of Harber's type for the concentration-time relation.
4. It seems probable that not only the elevated pCO₂ due to CO₂ inhalation, but also magnitude of dpCO₂/dt affects the cortical functions, even though only transiently.