128 Metabolism of Healthy Max. 



Factors Influencing Pulse-Rate. 



The pulse-rate is influenced by many factors, chiefly muscular activity and 

 the ingestion of food, and yet even with subjects who remain quietly sitting 

 and without food there may be considerable variations from day to day and 

 from hour to hour. Even the slight muscular activity incidental to sitting 

 up and to the quiet life in a respiration chamber may produce noticeable varia- 

 tions in pulse-rate from day to day. In a fasting experiment previously re- 

 ported, 1 the pulse-rate on the first day varied from 68 per minute at 7 h 30 m a. m. 

 to 51 at 10 p. m. These observations were taken by the subject himself, who 

 had had considerable experience in counting his own pulse. The general ten- 

 dency of the average pulse-rate during the 7-day fast was to fall noticeably, 

 and on the last day it was 57 at 7 h 30 m a. m. and 41 at 8 h 05 m p. m. It is thus 

 seen that eliminating the two most potent factors influencing the pulse-rate, 

 namely, the ingestion of food and muscular exercise, there is still opportunity 

 for considerable variation. 



Methods of Counting Pulse-Rate. 



In connection with the experiments here reported, a large number of obser- 

 vations of the pulse-rate were taken. In many instances they were recorded 

 by the subjects themselves, who were inside the respiration chamber, quietly 

 seated. These subjects were requested to count their radial pulse for 2 minutes 

 at frequent intervals during the day. At times an ordinary watch was used and 

 at other times they were given a stop-watch and a regular number of beats, 60, 

 was counted and the time required was noted. 



Believing there was some tendency to quicken or retard the pulse-rate by 

 having the subject take it himself, arrangements were made to record more or 

 less automatically the pulse-rate of the subjects by means of a pneumograph 

 so placed over the apex of the heart that the pulse-beat could be counted. The 

 apparatus and method of using it have been described in some detail else- 

 where. 2 With this apparatus, the pulse-rate could be counted by an observer 

 outside the chamber, whether the subjects were asleep or awake, and the air 

 transmission was so adjusted that a graphic record could be made if desired. 

 The larger amplitude of the pointer resting on the tambour indicated the 

 respirations, while the minor superimposed fluctuations indicated the pulse- 

 rhythm. Subsequently, it has been found desirable to utilize a stethoscope 

 attached to the body directly over the apex-beat of the heart, and this gives 

 results even more satisfactory than the pneumograph, for it frequently hap- 

 pened that the pneumograph became slightly displaced or the pulse-beat was 

 so feeble as to render accurate counting impossible. 



1 Benedict, Carnegie Institution of Washington Publication No. 77, 1907, p. 169. 



2 Benedict, loc. cit., p. 10. 



