ANATOMY AND PHYSIOLOGY.
Upon the difference of Temperature between Venous and Arterial
Blood. By G. V. Liebig.—Former investigations upon this subject
have led to conflicting results. Most of the older observers, such as
Haller, Crawford, Kramer, Scudamore, &c., having declared, that the
arterial blood (in the left cavities of the heart) is warmer than the venous
blood of the right cavities by 1°; while A. Cooper, Coleman, Mayer,
Autenrieth, etc., either pronounce the temperature of both kinds of
blood equal, or give to the venous blood an excess of temperature over
the arterial of 0-5°. The author proceeds, in his attempts to explain
these differences, to inquire, whether the higher temperature be found in
the blood flowing from the lungs, or in that from the capillaries, and he
reverts to some of his former observations upon “ muscular respiration.”
The experiments .were conducted both upon living and recently-killed
animals. That death might be caused quickly, and without loss of
blood, the medulla oblongata was severed in some instances, and narcotin
was administered in others. The thermometer was introduced, either
by the jugular vein or the carotid artery, to the requisite depth of the
heart; or it was inserted into the crural vein, or the vena cava abdomi-
nalis. Respiration was prolonged after death, when necessary. The
experiments were performed upon dogs, and with every possible precau-
tion to avoid errors,
The results were—-1. That the temperature of the blood in the right
cavities of the heart exceeds that of the left cavities by 0-05°; 2. That
the blood flowing into the heart by the vena cava descendens is cooler
than that from the vena cava ascendens (probably because the blood
which the former vessel contains comes from parts which presents to the
atmosphere a very great extent of surface in which a process of cooling
takes place.)
In the venous system, there go on changes of temperature correspond-
ing with the respiratory act. In the vena cava superior it was re-
marked that at the end of each inspiration the temperature of the blood
rose ; between inspiration and expiration it attained its maximum; to-
wards the end of expiration it fell; and was at its lowest point after
expiration. When animals breathe, or rather expire, shortly and quickly,
and then inspire deeply, the variations of temperature are greater than
usual. When the thermometer is in the right auricle, the highest de-
gree corresponds with inspiration, and the lowest with the beginning of
expiration. When the breathing is very short and hurried, these changes
of temperature become diminished, or even cease altogether. In the
vena cava abdominalis the same phenomena were not observed ; in the
vena iliaca they were reversed, the maximum occurring after expiration,
and the minimum after inspiration.
The author then remarks upon the mechanical influence exerted by
the respiratory movements upon the circulation in veins. The enlarge-
ment of the thoracic, and the diminution of the abdominal cavities,
coincident with inspiration, cause the blood of the vena cava ascendens
to flow into the right auricle, during and especially at the end of inspira-
tion. The conteuts of the vena cava descendens are less than those of
the vena cava ascendens, and they are cleared out at the beginning of
inspiration. During expiration the abdominal cavity is widened, and the
vena cava abdominalis gains both in space and contents. Towards the
end of inspiration, the auricle will therefore be filled by the warm blood
of the vena cava abdominalis; and at this moment is observed the highest
degree of variation in the heart’s temperature. In expiration the blood
streams into the auricle chiefly from the vena cava descendens, and then
is remarked the minimum of temperature. As regards differences of
temperature in different parts of the same system, the author found the
blood of the vena cava sup. 0.16°, and that of the auricle 0.20°. Be-
tween the auricle, where the blood from two vessels of different tempera-
ture is not completely mixed, and the ventricle, the difference amounted
to 0.1—30,20°.
In the arterial system there are no variations dependent upon the
movements of respiration, or they are very slight, amounting to 0 01—»
0.06°, and connected with the changes in the right cavities of the
heart, and the cooling of the blood in its passage from the lungs.
In dead animals, the temperature of the blood of the right ventricle
exceeds that of the left by 0-16°. In two experiments, however, the
temperature was found the same in both cavities. The temperature of
the blood of the vena cava abdominalis was once, upon opening the chest,
found l’TS9 higher than that of the thoracic portion of the carotid dur-
ing life. The same observations were repeated in several experiments.
The blood of the vena, cava abdominalis, which comes from the capillaries
of the lower extremities, and of some of the abdominal viscera, is the
warmest blood in the body, even in animals where the heart has been
emptied by bleeding, and to this point the author attaches great im-
portance.
It would be desirable to know the amount of cooling which the blood
undergoes in its passage through the lungs ; but the subject is fraught
with difficulty. The fact, however, if established, is most important,
inasmuch as the source of animal heat has been referred by many to the
organs of respiration. As regards the warmth of the blood in the vena
cava abdominalis, it must be remembered, that the vessel lies imbedded
in soft, highly organised parts, where, under all circumstances, heat is
retained for a longer time than in other parts of the body ; and perhaps
this fact will explain the cause of the warmth of blood in that vessel as
satisfactorily as any theory of changes going on in the capillary system.
—Med. Times, from Schmidt’s Jahrb., 1853.