The pulse-rate data, which have been presented and discussed in preceding pages, were in all cases recorded from counts at the wrist. During the collection of these data, no subject or observer ever noted irregularity at the time of making the pulse counts. There were no apparent cardiac symptoms, even after hard muscular work. (See page 453.) The pulse-rate appeared to decrease with fair regularity with the progress of the experiment. It seemed highly improbable that the slow rates of 35 or less were due to disturbances in conduction such as a regular 2:1 heart block, i. e., failure for every other auricular impulse to get through to the ventricles, or to the complete dissociation of auricles and ventricles characteristic of the Stokes-Adams syndrome. In the latter case, it is well known that the independent rate of the ventricles is usually about 32 per minute. Convincing proof in this matter of the normality of heart action in these slow pulse-rates associated with reduced diet could of course be had through graphic records, such as electrocardiograms taken under standard conditions.

It was desirable to interfere as little as possible with the Boston experimental program. This work could not be done in Springfield, and rather than take electrocardiograms from every subject, it appeared more satisfactory to take such tracings from only the 4 or 5 subjects who showed the slowest pulse-rate. Connections were therefore arranged from the string galvanometer in the main psychological laboratory to the group respiration chamber in the calorimeter room. The electrodes used in the respiration chamber were of the non-polarizable, wick form. A long strip of cotton gauze soaked in a saline solution was wrapped about the arm and the end of this dipped into a vessel of the saline solution. The distance between the arm and the vessel was about 7 inches. A porous clay cup containing the amalgamated zinc electrode and zinc sulphate was also placed in the vessel of saline solution. Such electrodes were connected with each arm, while the left foot of the subject was placed in a vessel of saline solution. On the morning of December 20, when the subjects were in the post-absorptive condition and before any of them were awake, the observers entered the chamber to connect them in turn to the string galvanometer. They had, of course, previously been informed what was to be done. It was, however, impossible to connect a subject without waking him and without stimulating the circulation more or less. The men remained very quiet; most of those who were not used as subjects continued sleeping. Tracings from the three standard leads were taken for Kon, Pea, and Pec. Even though the arms and left foot were bathed in an alcohol solution to reduce the tissue resistance, this remained, in general, quite high, i. e., from 4,000 to 9,000 ohms, in spite of the fact that an interval was allowed for the skin to become soaked and in good conducting condition.

Even with three observers cooperating it required some time to secure satisfactory tracings from a subject, and since tissue resistance under these conditions was higher than desired, it was decided to continue taking the records with the subject reclining in a steamer chair rather than lying on his back. Both arms and the left foot were placed in large pans of saline solution, which were arranged as non-polarizable electrodes. In this way a minimum of time was required in adjusting the subject to the electrodes, and there was a good opportunity for him to become relaxed and indifferent to the conditions. Thus, in the later records of the morning of December 20, the subject walked up the steps out of the respiration chamber and down another stairway to the level of the floor, stopped at the urine jar, and then came directly to the psychological laboratory, where he reclined in a steamer chair. Tracings from the three standard leads were taken in this position for Bro, Kon, Moy, Pec, and Yea. The tissue resistance under this condition ranged from 600 to 3,500 ohms.1

On February 2 at 4 p. m. - i. e., just before the standard evening meal - three of the subjects on whom electrocardiograms had previously been taken came to the Laboratory again for this purpose. These men, Kon, Pea, and Vea, were selected as their pulse-rates were as low as those of any in the squad, if not, indeed, the lowest; furthermore, as these subjects had served in this capacity previously, they would be but little affected by the novelty of the procedure. Arrangements were made on the balcony in the psychological laboratory so that the men could recline upon cote for about 20 minutes before the tracings were taken. The immersion electrodes were again used, and the men reclined in a steamer chair for the measurements. The tissue resistance ranged from 800 to 2,000 ohms; in general the conditions seemed very favorable.

1 Duplicate records were taken (or Pec and Kon, since those made when these subjects were in the respiration chamber were under conditions of 9,000 and 8,000 ohms tissue resistance, respectively.

Fig. 90. - Electrocardiograms for Kon and Pec. A, B, and C, from L1 L2, and L3 for Kon in group chamber, resistance 9,000 ohms; D from L2 for Pec, in group chamber, resistance 8,000 ohms.

The tracings for the two days from the standard leads designated L1, L2, and L3 are shown in table 83 as pulse-rates per minute. These range from 35 to 54; in the case of every subject lower pulse-rates were found at some other time during the investigation. This would naturally be expected. The subjects were thoroughly accustomed to having the pulse counted at the wrist, but this was not the case with the electrocardiographic tracings. Furthermore, both of the dates, December 20 and February 2, came at the end of a period of weight maintenance, during which time the amount of food was somewhat larger than at other periods. Since there was a noticeable correlation between the height of the pulse-rate and the energy intake, it could not be expected that the pulse would be as low here as it was, for example, at the middle of November. Nevertheless, the pulse-rates in the tracings which were made are mostly on a definitely lower plane than is commonly accepted as the normal pulse-rate for men of this age. The records taken in the chamber before the men got out of bed show especially slow rates, being 35 to 38 for the three men, Kon, Pea, and Pec.

If there were any pathological conditions to be found in the electrocardiographic tracings with the subjects on whom we took records in this low diet investigation, we would deem it necessary as important data of the experiment to publish all the tracings. Several of the tracings with explanatory legends are presented in figures 88, 89, and 90. In selecting the illustrations our only preference was to show those tracings which demonstrated the slower pulse-rates. Only normal electrocardiograms were shown by all of the subjects in every lead.

The usual chief deflections, P, R, and T, are present in their normal sequence and with no appreciably altered time relations. The waves are regular and of usual amplitude, and in no case is any certain wave absent or present in excessive number, that is, there are no extra systoles. There is no pathological arrhythmia, and absolutely no indication of heart block. Thus it is certain that the standard electrocardiograms demonstrate no abnormality other than the slow rate. The condition would appear to be classifiable as a sinus Bradycardia. This condition of slow, regular pulse-rate is known to occur normally in convalescence, old age, and pregnancy. These standard electrocardiograms taken in connection with our research seem to demonstrate that sinus Bradycardia may also normally occur with a lowered metabolism resulting from reduced diet. Since the electrocardiograms indicate normal heart action, it would appear that in addition to such factors as sex and age we must also add nutritional level as exercising a prominent influence upon the pulse-rate level. It is important that the conditions found in this experiment may exist with no cardiac discomfort or dyspnea.

Table 83. - Pulse-Rates Shown By The Standard Electrocardiograms