CHAPTER XX
THE INFLUENCE OF OXYGEN ADMINISTRATION ON THE CONCENTRATION OF THE BLOOD WHICH ACCOMPANIES THE DEVELOPMENT OF LUNG EDEMA a
The enormous and rapid development of edema of the lungs which results from severe gassing of animals with the lung irritants used in warfare offers an unusual opportunity for studying the physiological effects accompanying this pathological condition. The rapidity with which the edema develops precludes the possibility of infection complicating the symptoms observed, anti the condition which may develop after exposure to high concentrations of poisonous gas is so severe that the correlated symptoms can hardly be overlooked.
Loss of water from the blood is one of the most characteristic phenomena accompanying the development of edema of the lungs in animals gassed with lung irritants. A concentration of the blood becomes evident at about the time when the edema of the lungs can be first demonstrated. Thereafter the loss of water from the blood and the increase in severity of the edema run roughly parallel. The conclusion was made, therefore, that the two are interrelated and that the pouring of water into the lungs is the cause of the concentration of the blood.
Other considerations, however, make it necessary to proceed with caution before accepting this hypothesis. During the acute period after gassing there develops a deficiency of oxygen carried by the blood. Probably due to the poor aeration of the blood in the damaged lung the oxygen content of arterial and venous blood may drop to levels much below normal. The transport of oxygen to the tissues may be still further reduced by the decreased rate of blood flow, with the probable result that the oxygenation of the tissues is seriously interfered with.
Physiologists have shown that muscle tissue imbibes water when supplied with insufficient oxygen. Based on this observation, the hypothesis may be presented that the concentration of the blood is due not primarily to the development of lung edema but to the imbibition of water from the blood by the tissues which are not sufficiently oxygenated. To throw some light on the validity of this hypothesis the experiments reported below were carried out.
Goats were gassed with lethal concentrations of chloropicrin. As soon as possible after gassing, half of the animals were fitted with masks and given oxygen continuously in known quantities by means of a Haldane oxygen apparatus.b The other animals were used as controls.
The hemoglobin content was used as an index of the concentration of the blood. Hemoglobin determinations were made frequently, using blood obtained by pricking an ear vein. Blood from the heart punctures was also used. The Haldane method was used for the hemoglobin determinations.
a This chapter, which deals with the experimental observations of Capt. D. W. Wilson, C. W. S., and Capt. S. Goldschmidt, C. W. S., made in the physiological laboratories of the Royal Engineers Experimental Station, Porton, England, is reprinted in full from the American Journal of Physiology. Baltimore, 1919, No. 1, 157-164.
b The Haldane oxygen apparatus furnishes oxygen to a mask fitted with valves for incoming and outgoing air. When the mask is worn by the animal, breathing is easy and the air in the mask may be enriched by varying amounts of oxygen.
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When the concentration of the blood was sufficiently marked in the animals to which oxygen was being administered, heart punctures were made and the percentage saturation of the hemoglobin of the bloods from the right and left hearts was determined by means of Barcroft's differential blood gas apparatus.c Some difficulty was experienced in obtaining blood from the hearts of animals in which the lungs were large and edematous, but the sample was considered satisfactory when it was obtained quickly and with little struggling on the part of the animal.
The following protocols give the results obtained in this series of experiments:
CHART
c We are indebted to Mr. Barcroft, Captain Dunn, and Captain Peters for these data.
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CHART
Curves showing the concentration of the blood are reproduced in Charts XXIX, XXX, XXXI. In the charts, the percentage variations from the normal are plotted to make all of the curves directly comparable.
The maximum concentrations observed in the control animals varied from 30 percent to 60 percent above normal (average 43 percent), while in the animals receiving oxygen the variation was from 28 percent to 75 percent above normal (average 48 percent). It is apparent that, on the whole, the blood of animals which received oxygen concentrated as rapidly and to as great an extent as that of the control animals.
In order to demonstrate the efficiency of the oxygen administration, samples of blood were taken from both sides of the heart at suitable intervals and analyzed for oxygen. In most of the experiments the venous and arterial blood samples were obtained from the heart without difficulty and contained hemoglobin which was normally saturated with oxygen. With the increased concentration of the hemoglobin the oxygen content of the blood was even above normal.
Occasionally the blood was obtained only after considerable struggling on the part of the animal, so that the reduced oxygen content of such bloods was to be expected. These observations are reported here merely to make the experimental record complete, as obviously the low oxygen content of such bloods is without bearing on the present problem.
These experiments demonstrated that, by breathing oxygen-rich atmospheres, oxygen could be absorbed through the damaged and edematous lungs in quantities sufficient to maintain a practically normal level of oxygen in the arterial blood. The high saturation of the hemoglobin of venous blood with oxygen
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CHART XXIX- Changes in hemoglobin of the blood after gassing with chloropicrin 1/8500 for twenty-five minutes. Solid line: Animals receiving oxygen. Broken line: Control animals
CHART XXX.- Changes in hemoglobin of the blood after gaesing with chloropicrin 1/8500 for thirty minutes. Solid line: Animal receiving extra oxygen. Broken line: Control animal
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would seem to prove that the blood flow was sufficiently rapid to normally oxygenate the tissues. Nevertheless, in spite of the normal oxygenation of the tissues in the animals receiving oxygen, the blood concentrated as rapidly and to as great an extent as in the control animals. The conclusion therefore seems justifiable that the lack of oxygen in the tissues and consequent imbibition of water is not an important factor in causing the concentration of the blood in animals developing edema after being gassed with lung irritants.
An indication of the severity of the lung edema was obtained by comparing the weight of the lung to the weight of the heart at autopsy. The high lung to heart ratios obtained in practically all of the animals studied show that a severe grade of edema had already developed. The extent of the edema as indicated by this method was as great in the animals receiving oxygen as in the
CHART XXXI.- Changes in hemoglobin of the blood after gassing with chloropicrin l/S54O for twenty-five minutes. Solid line: Animals receiving extra oxygen. Broken line: Control animals
controls. Although the data are necessarily few, it is apparent that the efficient oxygenation of the lung tissue in the animals receiving oxygen failed to diminish the tendency for the development of the edema of the lungs.
With the enormous accumulation of fluid in the edematous lungs and the loss of water from the blood running roughly parallel, it is a tempting study to estimate even in a rough way the possible water interchange. An attempt has been made with data which are more or less incomplete and with calculations involving gross errors but the relations are so striking that they are presented in Table 94. In this table are recorded data and calculations from animals in which the hemoglobin was not determined immediately before death but is estimated from the curve obtained from the various determinations. These estimated values are quite similar to average values obtained at death on other animals.
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TABLE 94.- Comparison of calculated amounts of fluid lost from blood and extra fluid in the lungs of gassed animals
Examining the last two columns of the table it is evident that in only one instance the amount of extra fluid in the lung was less than the calculated loss of fluid from the blood. In some instances the extra fluid in the lung was much greater than that lost by the blood. Little or no water was drunk by goats in this condition and the volume of urine excreted was small, so that the external factors did not confuse the picture. Even with the relatively large errors of calculation involved, the conclusion seems justified that the loss of fluid by the blood could be accounted for by the excess of liquid in the edematous lung.
The evidence suggests that the muscles, etc., do not imbibe water and cause the concentration of the blood. In fact it would appear that water may be drawn from some tissues to make up part of the volume of liquid in the lung. One is thus finally led back to the original point of view that the development of the edema of the lungs and the concentration of the blood are interrelated, and are the important factors in the pathological condition studied. With this fact established it is justifiable to conclude that the development of the edema of the lungs is the primary factor in the condition and that the development of the edema causes the concentration of the blood.
SUMMARY
The continuous administration of oxygen to goats gassed with chloropicrin did not inhibit the concentration of the blood.
The percentage saturation of the hemoglobin with oxygen was normal even after a considerable concentration of the blood had occurred.
The concentration of the blood is not caused by the imbibition of water by the tissues as the result of oxygen want.
The loss of water from the blood is therefore due to the development of the edema of the lungs.
