CARBON-DIOXIDE CONTENT OF THE ALVEOLAR AIR AFTER MUSCULAR WORK.

A possible explanation for the low respiratory quotients usually found in the rest periods immediately following the muscular work might be that they were due to a storage of carbon dioxide in the body instead of to a change in the character of the katabolism. Thus, if the residual carbon dioxide in the body were larger at the end than at the beginning of the period, the amount of the carbon dioxide expired would not indicate the amount produced, so that the respiratory quotient would not be a true index of the nature of the material burned in the body. It is possible that during work organic acids (especially lactic acid) in the blood might replace in part the carbon dioxide as a factor stimulating the respiratory center; this would cause a smaller carbon-dioxide content of the arterial blood. After cessation of work, such acids would doubtless soon disappear so that the carbon-dioxide content of the blood would gradually return to a normal value. If there were a larger residual amount of carbon dioxide in the body at one time than at another, TABLE 131.-Determinations made on alveolar air with subject M. A. M. (without food).

1 The results for this day are post-absorptive values as usual but following 2 days with carbohydrate-poor diet (100 grams carbohydrates per day).

2 The results for this day are post-absorptive values as usual but following 3 days with carbohydrate-poor diet (100 grams carbohydrates per day).

3 The results for this day are post-absorptive values as usual but following 3 days with carbohydrate-rich diet (400 grams carbohydrates per day).

Lying.

.70

Lying..

5.78

40.9

.77

.77

it would be expected that the carbon dioxide in the alveolar air would also be relatively increased. Accordingly in a number of experiments with the subject M. A. M., samples of the alveolar air were taken at the beginning and end of some of the resting periods following the muscular work and analyzed by Mr. H. L. Higgins for carbon dioxide, the Haldane method being used." The results are summarized in table 131, together with the respiratory quotients which were obtained at approximately the same time.

By reference to the table, it will be seen that the data are given for six periods following work, these being lettered A to F. The only period in which there is a marked difference shown between the alveolar carbon dioxide found at the beginning and that found at the end of the period is B, but this difference is not seen in A or C for the same day, although the respiratory quotients for these two periods are much lower. The data for D and E, and especially F, also show clearly that the low respiratory quotient following work was not due to a storage of carbon dioxide in the body. Consequently one must look elsewhere for an explanation of these low quotients after work.

COLLAPSE FROM EXCESS OF CARBON DIOXIDE IN THE VENTILATING CURRENT.

During the first few experiments with this apparatus, two or three subjects shortly after the beginning of the severe riding utterly collapsed. At first we were at a loss to account for this, but it was soon found to be due to an excessive accumulation of carbon dioxide in the system, and the rebreathing by the subject of the carbon-dioxide rich air; measures were therefore immediately taken to remedy this defect.

One of the experiments in which this collapse occurred was that of November 22, 1911, with the subject J. E. F. The first three rest periods were uneventful, the pulse-rate averaging 59 per minute. The subject then rode the bicycle ergometer for some 20 minutes before the pulse-rate became reasonably regular at 122 per minute. After the mouth was placed to the mouthpiece and the valve was turned, he collapsed within 2 minutes. His face became pallid, almost cyanotic; he broke out into a cold sweat, and the pulserate rose suddenly from 124 to 184 per minute. The subject was neither able to retain the mouthpiece in the mouth nor to keep his feet on the pedals, having completely lost muscular control. As quickly as possible he was removed from the ergometer, placed upon the couch and allowed to rest. Twenty minutes later, the pulse-rate had almost returned to the normal and he reported himself as being quite comfortable. Indeed, somewhat later he was ready for a work experiment which was carried out without inconvenience.

Two days later, November 24, 1911, the same subject attempted another experiment. As in the first experiment, the three resting-periods were uneventful. After 10 minutes of preliminary work upon the bicycle ergometer, with an average per minute of 59 revolutions, it was found that the pulse-rate was regular at about 124. The first work experiment was then begun and lasted approximately 10 minutes, the work being done at the rate of 57 revolutions per minute. The pulse-rate rose to 146 and the respiration-rate to 24, but no abnormalities were noted. Ten minutes after the conclusion of the first period, a second period was begun, but within 4 minutes the subject showed all the symptoms of collapse, including pallor, gasping, lack of muscular cona Haldane and Priestley, Journ. Physiol., 1905, 32, p. 225.

trol of the hands, feet, and lips, cold sweat, giddiness, and rapid pulse-rate. The symptoms developed very suddenly, as the subject said before the beginning of the period that he felt perfectly well, this statement being corroborated by the fact that the pulse- and respiration-rates had both fallen in the intermission between the two working periods. He was immediately transferred to the couch and after 14 minutes was found to be in extremely good condition, the pulse-rate having fallen to 72 and the respiration-rate to 11 per minute. As it was thought that the subject might have a weak heart, an examination was made by E. P. C., who found no evidence of this. A confirmatory examination was made by Prof. D. L. Edsall who was at that time working in the Nutrition Laboratory, and his findings were also negative.

The experiment on December 13, 1911, with the professional subject M. A. M., likewise has an interest in this connection. The three restingperiods were without incident, as were also the three periods in which the subject rode without load. At 11h 05m a.m., the current was passed through the magnet and the work period began at 11h 21m a.m. The subject reported that he found moving the wheel with resistance very hard work, the effort required being more like that necessary for hill-climbing than for track-racing. One record of the pulse-rate made during the work showed 116 beats per minute. Soon after the period began, the subject looked flushed; a few minutes afterwards he perspired freely, and at 11h 25m a.m. he was obliged to discontinue his efforts as he was on the point of collapse. In appearance he was wild and scared, his face was pallid, his mouth twitching, and he had lost the control of his muscles, being unable to grasp the handle bars or to speak when he stopped.

The subject said that although he had collapsed in races, yet he had never felt so ill as he did at this time. He was much chagrined at his failure to continue and in order to convince the observers that the apparatus and not he was at fault, he again commenced riding, assuming what he called his "racing position," in which he lay over the handle-bars with his arms well back. With apparent ease and certainly without signs of collapse, he made 138 to 140 revolutions of the wheel per minute. In this test he did not breathe through the mouthpiece.

On the next day (December 14), the amount of work performed in the experiment was controlled by using a metronome, so as to restrict the subject to but 60 revolutions per minute. Before the experimental period began, the subject rode for a preliminary period of 22 minutes. Throughout the working period, while breathing through the apparatus, he was bathed in perspiration and at the end of 10 minutes signalled that he could not continue; he began to sway in his seat, and the experiment was immediately stopped. The records of the pulse-rate for the working period are extremely interesting. The experimental period began at 10h 29m a.m.; at 10h 31m a.m., the pulserate was 124 per minute; at 10h 33m a.m., it was the same; at 10h 35m a.m., it had risen to 128; at 10h 37m a.m., to 134; at 10h 39m a.m., to 142; and at 10h 39m 30 a.m. to 152 per minute, at which time he signalled for the experiment to be discontinued. The rapid rise in the pulse-rate is characteristic of impending collapse which was here present.

In a third experiment on December 15, the subject also showed signs of collapse in the third working-period, although the two preceding periods were

uneventful. The pulse-rate in the third period rose rapidly, the records being: 10h 50m a.m., 124; 10h 52m a.m., 128; 10h 54m a.m., 130; 10h 56m a.m., 132; 10h 58m a.m., 136; at which time the experiment was discontinued.

As the result of a careful examination of the results of the experiments in which the indications of collapse appeared, it was decided that these symptoms were due to an accumulation of carbon dioxide in the ventilating system, caused either by using defective soda-lime or too slow a rate of ventilation. Furthermore, the possible discomfort and strain on the part of the subject in holding his head in the position required by the rigid brass pipe to which the mouthpiece was attached should if possible be avoided. Several modifications were therefore made in the apparatus and in the experimental routine. Since these have already been noted in the description of the apparatus (see p. 29), a brief description will suffice here.

To insure complete absorption of the carbon dioxide by the soda-lime, the composition of this absorbent was somewhat modified in accordance with the results of a series of experiments which had recently been made for testing it; furthermore, two soda-lime containers were used in series so that any carbon dioxide which might pass the first container would be completely absorbed in the second; finally, the efficiency of the soda-lime was tested in every experiment by deflecting a small part of the air-current after it passed the carbon-dioxide absorbers and sending it through a solution of barium hydroxide before returning it to the system, the presence of excess carbon dioxide being readily detected by this method. Since it was found that the rate of ventilation was not rapid enough to remove the expired air as fast as the subject breathed into the pipe, a larger pulley was placed upon the armature shaft of the motor by means of which the rate of ventilation was increased from 35 to 60 liters and later to 85 liters per minute, this being found amply sufficient. To give more freedom of movement for the head in riding, a flexible tube was attached to the valve-piece through which the subject breathed. As this addition increased the dead air-space, a supplementary piece of rubber tubing was attached and the air-current was deflected through this so that it passed directly by the mouthpiece, thus eliminating the possible effect on the respiration of so large a dead air-space. This modification of the apparatus is clearly shown in fig. 3, page 29. After these changes in the apparatus and in the experimental routine had been made, practically all of the experiments were performed without any indications of collapse except on one or two occasions when the subject suffered some distress owing to the use of a defective soda lime bottle.

In the so-called fatigue experiment with M. A. M. on March 15, a collapse seemed imminent, although not actually occurring; this, however, was not in any way due to the presence of excess carbon dioxide in the ventilating system or to deficient ventilation, for not only was the absence of carbon dioxide proved by the barium hydroxide test but the amount of oxygen in the air was determined and found to be 22.5 per cent. The impending collapse was unquestionably due to the excessive muscular activity and the onset of fatigue.

Possible criticism may be made that the collapse in the earlier experiments was due not to an accumulation of carbon dioxide in the system but to a lack of oxygen. This was not true, as an analysis of the air in the apparatus

after each experiment showed that there was a sufficient supply of oxygen to meet the needs of the subject.

The observations of the pulse-rate in the experiments in which this collapse occurred are particularly noteworthy, the pulse rising in at least one experiment from 124 to 184 per minute inside of 2 minutes. Although the unusual conditions under which these pulse-rates were obtained do not make for the highest degree of accuracy, the records are not far from the actual values at the time the observations were made, as special care was taken to secure accurate records.

PULSE-RATE.

The intimate relationship between the pulse-rate and the muscular activity, or the degree of muscular rest, which has been observed so frequently in this laboratory not only with normal individuals but with pathological cases, with athletes and, indeed, with infants, emphasizes the importance of securing accurate records of the pulse-rate as an integral part of each experiment. When the subject is lying quietly on the couch, this may readily be done by means of a Bowles stethoscope lightly attached to the chest. During severe muscular work, however, these records were much more difficult to secure, and counts were therefore made of the radial pulse. When the subject rode at a high rate of speed with considerable lateral motion, accurate records even of the radial pulse were difficult to make so that only an experienced observer could be relied upon for these; accordingly, the records of the radial pulse were almost invariably taken by one of us (E. P. C.). Unfortunately, while the values obtained for the rest periods and subsequent to the work give admirable indications of the pulse-rate of the subject when at

0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 FIG. 6. Curves showing the pulse-rate when the external muscular work was equivalent to 1.05 calories per minute.

rest, those taken during work, especially if the work were of a high intensity, were of necessity more intermittent and can only be looked upon as general indices of the rate of the heart-beat. It soon became apparent that the pulse