Pulse and Respiration. 95 



not so clearly marked as is the beginning, partly because the contrac- 

 tion gradually decreased in vigor from second to second and the fall due 

 to the final relaxation was not so pronounced as was the rise at the 

 start. The period of muscular tension (tetanus) was approximately 5 

 seconds in duration. A clock beating seconds was in front of the oper- 

 ator, and by it the signals were given. Following the tetanus, the pulse 

 tracings became regular, all waves of the electro-cardiogram being dis- 

 cernible, and the record was continued for 20 to 25 seconds. We thus 

 have a continuous record approximately 35 to 40 seconds in length, 

 which makes possible the careful measurement of individual pulse 

 cycles during the following conditions: (1) subject comfortably resting; 

 (2) transition to severe muscular tension; (3) a section during which 

 muscular tension is continued ; (4) transition to rest ; and (5) a period of 

 recuperation. 1 



It is of course recognized that with condensers in series with the sub- 

 ject there is an alteration in the form of the waves of the electro- 

 cardiogram. The R wave is more prominent, while P and T are rela- 

 tively reduced. The condensers are necessary, however, to minimize 

 fluctuations of the base line, and these curves have been used solely for 

 determination of heart rate . With the technique as outlined, the P 

 wave is not always visible in the record ; it was therefore not practica- 

 ble to determine the length of pulse cycles by measuring from P to P. 

 As the peak of the R wave is always clearly marked in all the records, it 

 seems most practical to measure from one R peak to the next. Tech- 

 nically speaking, we are thus not measuring isolated individual pulse 

 cycles, but the duration obtained would represent the R-P of one pulse 

 cycle and the P-R of the next. Probably for our simple measurements 

 of rate this method does no great violence to the data, especially in 

 consideration of the fact that the duration between R and R can be 

 determined much more exactly than that from P to P. 



Pulse records such as those under discussion and illustrated in figure 

 11, A and B, are naturally considered in three divisions, which we have 

 termed for convenience (from left to right) pre-tetanus, tetanus, and 

 post-tetanus. As previously stated, it was not difficult in practice to 

 set the limit for the different parts, because of the disturbance in the 

 pulse and respiration tracings occasioned by the voluntary muscle con- 

 traction, although it was more difficult to mark the end of the tetanus 

 than its beginning. Each pulse cycle (from R to R, as previously 

 explained) was measured in tenths of millimeters. This distance, 

 divided by that which represents the corresponding second or seconds of 

 time on the time line made by a Jaquet clock below the pulse curve, 

 gives the length of the individual pulse cycle expressed in hundredths of 



1 In figure 31, p. 201 of Dodge and Benedict's report, it will be observed that frequently the 

 pulse at the end of post-stimulation had not reached the same level as that at the beginning of 

 pre-stimulation. For comments explaining this, see Appendix IV, p. 143, of this monograph. 



