INFLUENCE OF VARIOUS CONDITIONS ON RESPIRATION. 717 



of blood-pressure and a slowing of the pulse-rate. In the other 

 group the reverse relations hold, the blood-pressure and pulse-rate 

 both rising during the dyspneic phase and falling during the apnea. 

 This latter group consists of cases in which there is evidence of 



Fig. 282. Record showing typical Cheyne-Stokes respiration (from a case of aortic and 

 mitral insufficiency with arteriosclerosis). The time record gives seconds. 



increased intracranial tension. Under experimental conditions 

 the author was able to show on dogs that an artificial increase in 

 intracranial tension calls forth Cheyne-Stokes respirations, whenever 

 it happens that rhythmic changes in blood-pressure are produced 

 of such a character that the blood-pressure rises and falls alternately 

 above and below the line of intracranial pressure. It is probable, 

 therefore, that in the clinical cases associated with a rise of intra- 

 cranial pressure the blood-pressure likewise rises and falls above 

 and below intracranial tension, and that the alternating periods 

 of apnea and dyspnea are due to this fact in this class of cases. 

 When the blood-pressure falls below intracranial pressure there 

 is a condition of deep anemia of the medulla sufficient to suspend 

 the activity of the respiratory center. The following rise of blood- 

 pressure by forcing more blood through the medulla calls forth a 

 group of respiratory movements. 



By examination of the expired air Pembrey* has shown 

 that during the dyspneic phase the percentage of CO 2 in the 

 alveolar air is markedly diminished (2 per cent.), and he believes, 

 therefore, that the following phase of apnea is due entirely to 

 this washing out of the CO 2 , that is, to the removal of the normal 

 stimulus to the respiratory center. Practically he finds that 

 the apneic phase can be removed by the administration of 

 either pure oxygen or carbon dioxid (2.2 to 11.2 per cent.). 

 Pembrey does not give the clinical histories of his patients, but 



* Pembrey, "Journal of Pathology and Bacteriology," 12, 258, 1908. 



