654 PHYSIOLOGY OF RESPIRATION. 



as modified respiratory movements, since the same group of muscles 

 come into play. These are all movements, with the exception of 

 yawning, which may be regarded as reflexes that have nothing to 

 do directly with the processes of respiration. A most interesting 

 variation of the normal type of respiration is known as the Cheyne- 

 Stokes respiration. It occurs in certain pathological conditions, 

 such as arteriosclerosis, uremic states, fatty degeneration of the 

 heart, and especially under conditions of increased intracranial 

 pressure. It is characterized by the fact that the respiratory 

 movements occur in groups (10 to 30) separated by apneic pauses, 

 which may last for a number (30 to 40) of seconds. After each pause 

 the respirations begin with a small movement, gradually increase 

 to a maximum, and then fall off gradually to the point of complete 

 cessation (see Fig. 260). Great variations, however, are shown in 

 the character and number of the respirations during the so-called 

 dyspneic phase. From observations made by means of the 

 sphygmomanometer Eyster* has shown that in this condition 

 there are also rhythmic waves of blood-pressure (Traube-Hering 

 waves), and according to the relation of these pressure waves to 

 the groups of respirations the Cheyne-Stokes cases fall into two 

 groups. In one group the dyspneic phase coincides with a fall 

 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 

 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. More or less rhythmical varia- 

 tions in the strength of the breathing movements have been de- 

 scribed also in normal sleep, hibernation, chloral narcosis, etc., 

 but nothing so definite and characteristic as in these very interesting 

 Cheyne-Stokes cases. 



* Eyster, "Journal of Experimental Medicine," 1906. 



