Effects of Digitalis ox Vagus. 



37 



from vagus control might give relief, therefore, atropine gr. 1/30 

 was given by hypodermic injection. Record taken 27 minutes 

 later shows the ventricle beating irregularly at the rate of 150 

 per minute but uninfluenced by breathing. The patient became 

 comfortable and the cyanosis was less. 



Discussion. — As the slowing of the ventricular rate followed 

 the first inspiration after apnea and was maintained until the last 

 part of the hyperpnea stage, it was considered to be due to the 

 inhibition of the vagus which was stimulated by the reflexes from 

 the lung generated by the respiratory efforts of hyperpnea. The 

 average hyperpnea periods were of 37 sec. duration. The 

 reflex from the lung became much less effective as a stimulant to 

 the vagus during the descending phase of the hyperpnea; for, the 

 ventricular rate became accelerated several inspirations before 

 apnea began. 



This loss of vagus effect upon the heart rate was due, probably, 

 to the fact that reflex stimuli from the lung tissue when it is con- 

 tracting are not so strong as when the pulmonary tissue is being 

 distended, but not to true vagus escape of the heart. That the 

 vagus controlled the ventricular rate was shown by absence of 

 alterations of the ventricular rate while the atropine was effective. 

 During atropine effect the hyperpnea persisted for 47 seconds, a 

 ten second increase over the digitalis period. 



The distress of the patient was due to the diminished inter- 

 change of 0 2 and C0 2 between the lungs and blood. This inter- 

 change was least during apnea, when the pulmonary ventilation 

 was lowest though the heart rate was highest, but during hyper- 

 pnea, when the ventilation of the lung was greatest, the heart 

 rate was slowest. The sensitiveness of the vagus to the pul- 

 monary reflex was increased by digitalis to such a degree that the 

 number of ventricular contractions during hyperpnea were very 

 much less than when digitalis was not given. 



To state this in another way; it appears that without digitalis 

 the amount of interchange of 0 2 and C0 2 was sufficient, to keep 

 the patient comfortable, notwithstanding the inverse periodic 

 changes in rate of heart and breathing; but, when digitalis was 

 given, the vagus became much more susceptible to the lung re- 

 flexes slowed the circulation so as to diminish the interchange of 



