Rhythmic change in respiratory frequency has been observed in the pneumograph of CO gas breathing dogs. On the pneumograph of hyperpneic dog induced by CO breathing, rebreathing 1.8% of CO as initial concentration in 16 liters of oxygen, 4 to 10 (6 in average) rapider breathings were followed by 5 to 9(6 in average) slower breathings. The duration of 6 rapider breathings showed range of from 6.3 seconds to 12.2 seconds, averaging 8.8 seconds and the duration of about 6 slower breathings ranged from 11.2 seconds to 17.2 seconds, averaging 13.5 seconds.
To elucidate the possible mechanism of this rhythmic change in respiratory rate observed in 15 CO poisoning dogs, pneumographs were recorded with deep intention on the rhythmic rate changing respiration in 14 hypoxic dogs. In 6 dogs breathed CO₂ removing low O₂gas - rebreathing 16 liters of airthrough closed circuit- the phenomenon of rhythmic change in respiratory rate has had precisely observed. The unusual respiatory pattern of hyperpnea was also observed in 7 out of 8 dogs rebreathed air through closed circuit allowing accumulation of CO₂in the system.
In all CO poisoning or low O₂breathing groups, and during the course of the experiment in each case, the incidence of change of respiratory rate from slower to rapider rate is 3 times per minute even though the duration of rapider and slower breathing period showed slight changes according to the progress of CO poisoning or hypoxia and to the breathing condition of low O₂, CO₂ removing or CO₂ accumulating circuit.
Number of rapider breathings became greater making duration of the period longer by the increase in the degree of CO poisoning or of hypoxia. Particularly in the group of low O₂breathing with accumulation of CO₂the duration of rapider breathing period or number of rapider breathings is greater than those of slower breathings.
The appearance of the rhythmic change in respiratory frequency was most clear and prominent in CO poisoning group and was some-what obscure in CO₂accumulating low O₂breathing group.
The phenomenon of rhythmic change in respiratory rate is clearly observable only at the recorder speed of about 20 mm per minute. At the slower speed of recorder each respiratory curve fuses toand at the higher speed the cycle of change in respiratory rate appeared indistinctly.
At the moment of the rhythmic change in respiratory rate became to be observable prominently, the arterial CO saturation was 34.5% in average of 15 CO breathing dog Arterial O₂saturation was 67.2% in average of 6 CO₂removed low O₂breathdogs and was 51.6% in average of 7 CO₂acculow 02 breathing dogs.
The rhythmic change in respiratory rate appeared only in hyperpneic dogs and the phenomenon is abolished by intra-venous injection of anesthetics and was not observable in one dog in which tidal volume was very much increased (up to 1 liter) by rebreathing of CO₂accumulating low 02 gas.
As possible factors causing the rhythmic change in respiratory rate, hypoxia hypocapnea, pH chunge and some dis arrange-ment is respiratory center are considered. Most likely it seemed that no single factor can induce the rhythmic breathing by itself, but several factors, such as disarrangement in neural controland change in chemical stimuli, are responsible for the changes in respiratory frequency.
Possibility of that different part of respiratory center might predominantly controls respiratory rate or depth separately has been suggested. More likely it seemed that the part which might controls predominantly respiratory depth (tidal volume) is more sensitive to the increase in arterial pCO₂.
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