The sensitiveness of the respiratory centre to carbonic acid, and the dead space during hyperpnœa

IN a recent paper' attention has been drawn to the great sensitiveness of the respiratory centre to CO2. The actual experiments described in that paper indicated that a rise of about 03 0/0 in the alveolar CO2pressure was sufficient to cause the alveolar ventilation of the lungs to be increased by 1000/o above the resting value. At the same time arguments were advanced to show that in all probability this observed value was really too high, as, owing to the technique adopted, it was impossible to make allowance for any increase in the metabolism during the experiments, the alteration in the alveolar ventilation being deduced from a comparison of the differences of the concentration of CO2 in the alveolar and inspired airs. Supposing that the metabolism had been increased while air containing CO2 was being breathed the actual hyperpncea would have been greater than the calculated value indicated, and it was finally concluded that a rise of about 0-22 0/0 or 1-6 mm. of CO2-pressure in the alveolar air was really sufficient to cause an increase of 1000/0 in the alveolar ventilation. It was also shown that erroneous conclusions were likely to be drawn if the observations were made before the body had got into equilibrium with the particular 0O0 mixture breathed. In the course of some other experiments it became necessary to verify these conclusions as to the sensitiveness of the respiratory centre to C02, and to obtain some more precise quantitative relationship between the alveolar ventilation and the alveolar C02-pressure than is implied by the somewhat casual expression of 100 s/o increase above the resting ventilation.