CHAPTER XLI 

 THE CONTROL OF RESPIRATION (Cont'd) 



THE NATURE OF THE RESPIRATORY HORMONE 



The practical importance of the observations described in the foregoing 

 chapters in the investigation of the relationship between C H of the 

 blood and respiratory activity will now be plain, and it remains for us 

 to consider the physiological evidence that such a relationship exists. In 

 the first place, let us consider the behavior of the acid-base equilibrium 

 during conditions of abnormal breathing hyperpnea and dyspnea.* 



As C0 2 accumulates and O 2 becomes used up in a confined space, the 

 breathing becomes intensified. In searching for the exact cause of this 

 effect, we must first of all ascertain whether the hyperpuea is due to the 

 deficiency of 2 or to the accumulation of C0 2 or to both acting to- 

 gether. Many of the experiments bearing on these problems can be 

 more satisfactorily performed on man than on laboratory animals, be- 

 cause anesthesia is not necessary and the subjective symptoms experi- 

 enced are of great value in the interpretation of the results. If an in- 

 dividual is placed in a large air-tight chamber (2000 liters' capacity), 

 and the depth and rate of breathing observed as the C0 2 accumulates and 

 the 2 becomes used up in the air of the chamber, no distinct change in 

 respiration will be observed by the person himself until the C0 2 per- 

 centage of the air has risen to almost 3. Above this point, however, the 

 hyperpnea becomes more and more pronounced, until finally, when the 

 C0 2 percentage has risen to about 6 and the 2 percentage has fallen to 

 13.5, it becomes unbearable (dyspnea). From the results of the fore- 

 going observation alone we could not, however, decide whether the 

 excitation of the respiratory center is due to the deficiency of 2 or to 

 the increase of C0 2 . If the experiment is repeated with the difference 

 that the C0 2 as it accumulates is absorbed by soda lime, no perceptible 

 hyperpnea will develop even when the 2 is as low as in the previous 

 experiment. We may conclude, therefore, that in the first experiment 

 C0 2 accumulation must have acted as the main respiratory stimulus, and 

 that oxygen deficiency, if it stimulates at all, must do so to a less degree 

 than increase in C0 2 . 



*Hyperpnea means slightly increased breathing; dyspnea, labored breathing, but yet with suffi- 

 cient ventilation to maintain life; asphyxia, the results of insufficient breathing. 



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