Respiration Calorimeters for Studying the Respiratory Exchange and Energy Transformations of Man Part 9

----- ------ (b) 19706 = 1.57 l. CO_{2} " O + N = 691.56 l.

" N = 552.96 l.

------ " O = 186.57 l.

ABBREVIATED METHOD OF COMPUTATION OF OXYGEN ADMITTED TO THE CHAMBER FOR USE DURING SHORT EXPERIMENTS.

Desiring to make the apparatus as practicable and the calculations as simple as possible, a scheme of calculation has been devised whereby the computations may be very much abbreviated and at the same time there is not too great a sacrifice in accuracy. The loss in weight of the oxygen cylinder has, in the more complicated method of computation, been considered as due to oxygen and about 3 per cent of nitrogen. The amount of nitrogen thus admitted has been carefully computed and its volume taken into consideration in calculating the residual oxygen. If it is considered for a moment that the admission of gas out of the steel cylinder is made at just such a rate as to compensate for the decrease in volume of the air in the system due to the absorption of oxygen by the subject, it can be seen that if the exact volume of the gas leaving the cylinder were known it would be immaterial whether this gas were pure oxygen, oxygen with some nitrogen, or oxygen with any other inert gas not dangerous to respiration or not absorbed by sulphuric acid or potash-lime. If 10 liters of oxygen had been absorbed by the man in the course of an hour, to bring the system back to constant apparent volume it would be necessary to admit 10 liters of such a gas or mixture of gases, a.s.suming that during the hour there had been no change in the temperature, the barometric pressure, or the residual amounts of carbon dioxide or water-vapor.

Under these a.s.sumed conditions, then, it would only be necessary to measure the amount of gas admitted in order to have a true measure of the amount of oxygen absorbed. The measure of the volume of the gas admitted may be used for a measure of the oxygen absorbed, even when it is necessary to make allowances for the variations in the amount of carbon dioxide or water-vapor in the chamber, the temperature, and barometric pressure. From the loss in weight of the oxygen cylinder, if the cylinder contained pure oxygen, it would be known that 10 liters would be admitted for every 14.3 grams loss in weight.

From the difference in weight of 1 liter of oxygen and 1 liter of nitrogen, a loss in weight of a gas containing a mixture of oxygen with a small per cent of nitrogen would actually represent a somewhat larger volume of gas than if pure oxygen were admitted. The differences in weight of the two gases, however, and the amount of nitrogen present are so small that one might almost wholly neglect the error thus arising from this admixture of nitrogen and compute the volume of oxygen directly from the loss in weight of the cylinder.

As a matter of fact, it has been found that by increasing the loss in weight of the cylinder of oxygen containing 3 per cent nitrogen by 0.4 per cent and then converting this weight to volume by multiplying by 0.7, the volume of gas admitted is known with great accuracy. This method of calculation has been used with success in connection with the large chamber and particularly for experiments of short duration. It has also been introduced with great success in a portable type of apparatus described elsewhere.[27] Under these conditions, therefore, it is unnecessary to make any correction on the residual volume of nitrogen as calculated at the beginning of the experiment. When a direct comparison of the calculated residual amount of oxygen present is to be made upon determinations made with a gas-a.n.a.lysis apparatus the earlier and much more complicated method of calculation must be employed.

CRITICISM OF THE METHOD OF CALCULATING THE VOLUME OF OXYGEN.

Since the ventilating air-current has a confined volume, in which there are constantly changing percentages of carbon dioxide, oxygen, and water-vapor, it is important to note that the nitrogen present in the apparatus when the apparatus is sealed remains unchanged throughout the whole experiment, save for the small amounts added with the commercial oxygen--amounts well known and for which definite corrections can be made. Consequently, in order to find the amount of oxygen present in the residual air at any time it is only necessary to determine the amounts of carbon dioxide and water-vapor and, from these two factors and from the known volume of nitrogen present, it is possible to compute the total volume of oxygen after calculating the total absolute volume of air in the chamber at any given time.

While the apparent volume of the air remains constant throughout the whole experiment, by the conditions of the experiment itself the absolute amount may change considerably, owing primarily to the fluctuations in barometric pressure and secondarily to slight fluctuations in the temperature of the air inside of the chamber.

Although the attempt is made on the part of the observers to arbitrarily control the temperature of this air to within a few hundredths of a degree, at times the subject may inadvertently move his body about in the chair just a few moments before the end of the period and thus temporarily cause an increased expansion of the air. The apparatus is, in a word, a large air-thermometer, inside the bulb of which the subject is sitting. If the whole system were inclosed in rigid walls there would be from time to time noticeable changes in pressure on the system due to variations in the absolute volume, but by means of the tension-equalizer these fluctuations in pressure are avoided.

The same difficulties pertain here which were experienced with the earlier type of apparatus in determining the average temperature of the volume of air inside of the chamber. We have on the one hand the warm surface of the man's body, averaging not far from 32 C. On the other hand we have the cold water in the heat-absorbers at a temperature not far from 12 C. Obviously, the air in the immediate neighborhood of these two localities is considerably warmer or colder than the average temperature of the air. The disposition of the electric-resistance thermometers about the chamber has, after a great deal of experimenting, been made such as to permit the measurement as nearly as possible of the average temperature in the chamber. But this is at best a rough approximation, and we must rely upon the a.s.sumption that while the temperatures which are actually measured may not be the average temperature, the fluctuations of the average temperature are parallel to the fluctuations in the temperatures measured. Since every effort is made to keep these fluctuations at a minimum, it is seen that the error of this a.s.sumption is not as great as might appear at first sight.

However, the calculation of the residual amount of oxygen in the chamber is dependent upon this a.s.sumption and hence any errors in the a.s.sumption will affect noticeably the calculation of the residual oxygen.

Attempts to compare the determination of the oxygen by the exceedingly accurate Sonden apparatus with that calculated after determining the water-vapor and carbon dioxide, temperature and pressure of the air in the chamber have thus far led to results which indicate one of three things: (1) that there is not a h.o.m.ogeneous mixture; (2) that during the time required for making residual a.n.a.lyses, _i. e._, some three or four minutes, there may be a variation in the oxygen content in the air of the chamber due to the oxygen continually added from the cylinder; (3) that the oxygen supplied from the cylinder is not thoroughly mixed with the air in the chamber until some time has elapsed. That is to say, with the method now in use it is necessary to fill the tension-equalizer to a definite pressure immediately at the end of each experimental period.

This is done by admitting oxygen from the cylinder, and obviously this oxygen was not present in the air when a.n.a.lyzed. A series of experiments with a somewhat differently arranged system is being planned in which the oxygen will be admitted to the respiration chamber directly and not into the tension-equalizer, and at the end of the experiment the tension-equalizer will be kept at such a point that when the motor is stopped the amount of oxygen to be added to bring the tension to a definite point will be small.

Under these conditions it is hoped to secure a more satisfactory comparison of the a.n.a.lyses as made by means of the Sonden apparatus and as calculated from the composition of the residual air by the gravimetric a.n.a.lysis. It remains a fact, however, that no matter with what skill and care the gasometric a.n.a.lysis is made, either gravimetrically or volumetrically, the calculation of the residual amount of oxygen presents the same difficulties in both cases.

CALCULATION OF TOTAL OUTPUT OF CARBON DIOXIDE AND WATER-VAPOR AND OXYGEN ABSORPTION.

From the weights of the sulphuric-acid and potash-lime vessels, the amounts of water-vapor and carbon dioxide absorbed out of the air-current are readily obtained. The loss in weight of the oxygen cylinder increased by 0.4 per cent (see page 88) gives the weight of oxygen admitted to the chamber. It remains, therefore, to make proper allowance for the variations in composition of the air inside the chamber at the beginning and end of the different periods. From the residual sheets the amounts of water-vapor, carbonic acid, and oxygen present in the system at the beginning and end of each period are definitely known. If there is an increase, for example, in the amount of carbon dioxide in the chamber at the end of a period, this increase must be added to the amount absorbed out of the air-current in order to obtain the true value for the amount produced during the experimental period.

A similar calculation holds true with regard to the water-vapor and oxygen. For convenience in calculating, the amounts of water-vapor and carbon dioxide residual in the chamber are usually expressed in grams, while the oxygen is expressed in liters. Hence, before making the additions or subtractions from the amount of oxygen admitted, the variations in the amount of oxygen residual in the system should be converted from liters to grams. This is done by dividing by 0.7.

CONTROL EXPERIMENTS WITH BURNING ALCOHOL.

After having brought to as high a degree of perfection as possible the apparatus for determining carbon dioxide, water, and oxygen, it becomes necessary to submit the apparatus to a severe test and thus demonstrate its ability to give satisfactory results under conditions that can be accurately controlled. The liberation of a definite amount of carbon dioxide from a carbonate by means of acid has frequently been employed for controlling an apparatus used for researches in gaseous exchange, but this only furnishes a definite amount of carbon dioxide and throws no light whatever upon the ability of the apparatus to determine the other two factors, water-vapor and oxygen. Some of the earlier experimenters have used burning candles, but these we have found to be extremely unsatisfactory. The necessity for an accurate elementary a.n.a.lysis, the high carbon content of the stearin and paraffin, and the possibility of a change in the chemical composition of the material all render this method unfit for the most accurate testing. As a result of a large number of experiments with different materials, we still rely upon the use of ethyl alcohol of known water-content. The experiments with absolute alcohol and with alcohol containing varying amounts of water showed no differences in the results, and hence it is now our custom to obtain the highest grade commercial alcohol, determine the specific gravity accurately, and burn this material. We use the Squibb pyknometer[28] and thereby can determine the specific gravity of the alcohol to the fifth or sixth decimal place with a high degree of accuracy. Using the alcoholometric tables of Squibb[29] or Morley,[30]

the percentage of alcohol by weight is readily found, and from the chemical composition of the alcohol can be computed not only the amount of carbon dioxide and water-vapor formed and oxygen absorbed by the combustion of 1 gram of ethyl hydroxide containing a definite known amount of water, but also the heat developed during its combustion.

With the construction of this apparatus it was found impracticable to employ the type of alcohol lamp formerly used with success in the Wesleyan University respiration chamber. Inability to illuminate the gage on the side of the lamp and the small windows on the side of the calorimeter precluded its use. It was necessary to resort to the use of an ordinary kerosene lamp with a large gla.s.s font and an Argand burner.

Of the many check-tests made we quote one of December 31, 1908, made with the bed calorimeter:

Several preliminary weights of the rates of burning were made before the lamp was introduced into the chamber. The lamp was then put in place and the ventilation started without sealing the cover. The lamp burned for about one hour and a quarter and was then weighed again. Then the window was sealed in and the experiment started as soon as possible. At the end of the experiment the window was taken out immediately and the lamp blown out and then weighed. The amount burned between the time of weighing the alcohol and the beginning of the experiment was calculated from the rate of burning before the experiment and this amount subtracted from the total burned from the time that the lamp was weighed before being sealed in until the end, when it was weighed the second time. For the minute which elapsed between the end of the experiment and the last weighing, the rate for the length of the experiment itself was used.

During the experiment there were burned 142.7 grams of 92.20 per cent alcohol of a specific gravity of 0.8163.

A tabular summary of results is given below:

+----------------------+--------+-----------+ Found. Required. +----------------------+--------+-----------+ Carbon dioxide gms. 259.9 251.4 Oxygen " 278.5 274.8 Water-vapor " 165.8 165.6 Heat cals. 829.0 834.5 +----------------------+--------+-----------+

Thus does the apparatus prove accurate for the determination of all four factors.

BALANCE FOR WEIGHING SUBJECT.

The loss or gain in body-weight has always been taken as indicating the nature of body condition, a loss usually indicating that there is a loss of body substance and a gain the reverse. In experiments in which a delicate balance between the income and outgo is maintained, as in these experiments, it is of special interest to compare the losses in weight as determined by the balance with the calculated metabolism of material and thus obtain a check on the computation of the whole process of metabolism. Since the days of Sanctorius the loss of weight of the body from period to period has been of special interest. The most recent contribution to these investigations is that of the balance described by Lombard,[31] in which the body-weight is recorded graphically from moment to moment with an extraordinarily sensitive balance.

In connection with the experiments here described, however, the weighing with the balance has a special significance, in that it is possible to have an indirect determination of the oxygen consumption. As pointed out by Pettenkofer and Voit, if the weight of the excretions and the loss in body-weight are taken into consideration, the difference between the weight of the excretions and the loss in body-weight should be the weight of the oxygen absorbed. With this apparatus we are able to determine the water-vapor, the carbon-dioxide excretion, and the weight of the urine and feces when pa.s.sed. If there is an accurate determination of the body-weight from hour to hour, this should give the data for computing exactly the oxygen consumption. Moreover, we have the direct determination of oxygen with which the indirect method can be compared.

In the earlier apparatus this comparison was by no means as satisfactory as was desired. The balance there used was sensitive only to 2 grams, the experiments were long (24 hours or more), and it seemed to be absolutely impossible, even by exerting the utmost precaution, to secure the body-weight of the subject each day with exactly the same clothing and accessories. Furthermore, where there is a constant change in body-weight amounting to 0.5 gram or more per minute, it is obvious that the weighing should be done at exactly the same moment from day to day.

It is seen, therefore, that the comparison with the direct oxygen determination is in reality an investigation by itself, involving the most accurate measurements and the most painstaking development of routine.

With the hope of contributing materially to our knowledge regarding the indirect determination of oxygen, the special form of balance shown in fig. 9 was installed above the chair calorimeter. This balance is extremely sensitive. With a dead load of 100 kilograms in each pan it has shown a sensitiveness of 0.1 gram, but in order to have the apparatus absolutely air-tight for the oxygen and carbon-dioxide determination, the rod on which the weighing-chair is suspended must pa.s.s through an air-tight closure. For this closure we have used a thin rubber membrane, weighing about 1.34 grams, one end of which is tied to a hard-rubber tube ascending from the chair to the top of the calorimeter, the other end being tied to the suspension rod. In playing up and down this rod takes up a varying weight of the rubber diaphragm, depending upon the position which it a.s.sumes, and therefore the sensitiveness noted by the balance with a dead load and swinging freely is greater than that under conditions of actual use. Preliminary tests with the balance lead us to believe that with a slight improvement in the technique a man can be weighed to within 0.3 gram by means of this balance. A series of check-experiments to test the indirect with the direct determination of oxygen are in progress at the moment of writing, and it is hoped that this problem can be satisfactorily solved ere long.

During the process of weighing, the ventilating air-current is stopped so as to prevent any slight tension on the rubber diaphragm and furnish the best conditions for sensitive equilibrium. After the weighing has been made and the time exactly recorded, the load is thrown off the knife-edges of the balance, and then provision has been made to raise the rod supporting the chair and simultaneously force a rubber stopper tightly into the hard rubber tube at the top of the calorimeter, thus making the closure absolutely tight. It is somewhat hazardous to rely during the entire period of an experiment upon the thin rubber membrane for the closure when the blower is moving the air-current.

To raise the chair and the man suspended on it in such a way as to draw the cork into the hard-rubber tube, we formerly used a large hand-lever, which was not particularly satisfactory. Thanks to the suggestion of Mr.

E. H. Metcalf, we have been able to attach a pneumatic lift (fig. 9) in that the cross-bar above the calorimeter chamber, to which the suspension rod is attached, rests on two oak uprights and can be raised by admitting air into an air-cus.h.i.+on, through the central opening of which pa.s.ses the chair-suspending rod. As the air enters the air-cus.h.i.+on it expands and lifts a large wooden disk which, in turn, lifts the iron cross-bar, raising the chair and weight suspended upon it. At the proper height and when the stopper has been thoroughly forced into place, two movable blocks are slipped beneath the ends of the iron cross-bar and thus the stopper is held firmly in place. The tension is then released from the air-cus.h.i.+on. This apparatus functionates very satisfactorily, raising the man or lowering him upon the knife-edges of the balance with the greatest regularity and ease.

PULSE RATE AND RESPIRATION RATE.

The striking relations.h.i.+p existing between pulse rate and general metabolism, noted in the fasting experiments made with the earlier apparatus, has impressed upon us the desirability of obtaining records of the pulse rate as frequently as possible during an experiment.

Records of the respiration rate also have an interest, though not of as great importance. In order to obtain the pulse rate, we attach a Bowles stethoscope over the apex beat of the heart and hold it in place with a light canvas harness. Through a long transmission-tube pa.s.sing through an air-tight closure in the walls of the calorimeter it is possible to count the beats of the heart without difficulty. The respiration rate is determined by attaching a Fitz pneumograph about the trunk, midway between the nipples and the umbilicus. The excursions of the tambour pointer as recorded on the smoked paper of the kymograph give a true picture of the respiration rate.

Of still more importance, however, is the fact that the expansion and contraction of the pneumograph afford an excellent means for noting the minor muscular activity of a subject, otherwise considered at complete rest. The slightest movement of the arm or the contraction or relaxation of any of the muscles of the body-trunk results in a movement of the tambour quite distinct from the respiratory movements of the thorax or abdomen. These movements form a very true picture of the muscular movements of the subject, and these graphic records have been of very great value in interpreting the results of many of the experiments.

ROUTINE OF AN EXPERIMENT WITH MAN.

In the numerous previously published reports which describe the construction of and experiments with the respiration calorimeter, but little attention has been devoted to a statement of the routine. Since, with the increasing interest in this form of apparatus and the possible construction of others of similar form, a detailed description of the routine would be of advantage, it is here included.

PREPARATION OF SUBJECT.

Prior to an experiment, the subject is usually given either a stipulated diet for a period of time varying with the nature of the experiment or, as in the case of some experiments, he is required to go without food for at least 12 hours preceding. Occasionally it has been deemed advisable to administer a cup of black coffee without sugar or cream, and by this means we have succeeded in studying the early stages of starvation without making it too uncomfortable for the subject. The stimulating effect of the small amount of black coffee on metabolism is hardly noticeable and for most experiments it does not introduce any error.

The urine is collected usually for 24 hours before, in either 6 or 12 hour periods. During the experiment proper urine is voided if possible at the end of each period. This offers an opportunity for studying the periodic elimination of nitrogen and helps frequently to throw light upon any peculiarities of metabolism.

Even with the use of a long-continued preceding diet of constant composition, it is impossible to rely upon any regular time for defecation or for any definite separation of feces. For many experiments it is impracticable and highly undesirable to have the subject attempt to defecate inside the chamber, and for experiments of short duration the desire to defecate is avoided by emptying the lower bowel with a warm-water enema just before the subject enters the chamber. Emphasis should be laid upon the fact that a moderate amount of water only should be used and only the lower bowel emptied, so as not to increase the desire for defecation.

The clothing is usually that of a normal subject, although occasionally experiments have been made to study the influence of various amounts of clothing upon the person. There should be opportunity for a comfortable adjustment of the stethoscope and pneumograph, etc., and the clothing should be warm enough to enable the subject to remain comfortable and quiet during his sojourn inside the chamber.

The rectal thermometer, which has previously been carefully calibrated, is removed from a vessel of lukewarm water, smeared with vaseline, and inserted while warm in the r.e.c.t.u.m to the depth of 10 to 12 centimeters.