Ventilatory response to intermittent inspired carbon dioxide

The hypothesis that cyclic variation of CO2 tension of the arterial blood (PaCOCO2) about its mean produces an additional stimulus to ventilation was tested in the dog. Oscillations of alveolar carbon dioxide tension were produced by the intermittent administration of 20% CO2 for 1 breath every 7–12 breaths. The increment in ventilation per mm Hg rise in mean PaCOCO2 during the intermittent administration of 20% CO2 was compared to that during continuous administration of 3% CO2 in nine adult dogs anesthesized with sodium pentobarbital. Thirteen experiments with oscillating CO2 and eighteen with steady CO2 were performed. In all except one animal the increase in ventilation per mm Hg change in mean PaCOCO2 was greater during intermittent CO2 than during steady CO2. In three experiments intermittent administration of CO2 caused a ventilatory response sufficient to lower the mean PaCOCO2 below control values. The increment in total ventilation per mm Hg rise in arterial carbon dioxide tension for steady CO2 breathing was 0.58 liters/min per mm Hg and for intermittent CO2 was 2.00 liters/min per mm Hg. These findings support the concept that chemoreceptors are stimulated by oscillations of PaCOCO2 as well as by the mean level of PaCOCO2. The oscillatory stimulus appears not to be related to the amplitude of the oscillation or to the peak Pco2 attained, but rather to the rate of increase of arterial Pco2. respiration control; ventilation Submitted on October 17, 1963