Circulation / by Allen Thomson.

  • Allen Thomson
Date:
1836
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Licence: Public Domain Mark

Credit: Circulation / by Allen Thomson. Source: Wellcome Collection.

Provider: This material has been provided by The Royal College of Surgeons of England. The original may be consulted at The Royal College of Surgeons of England.

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    blood occasionally appears to exert within an aneurismal tumour; giving rise to its peculiarly hard pulsation on every side, and assisting the ravages by absorption which are frequently the consequence of the larger internal aneurisms. The pressure in an aneurism is obviously to be measured by the extent of its internal surface multiplied into the force with which the blood moves in the part of the artery where it opens into the aneurismal sac. c. Arterial pulse.—The arterial pulse, or suc- cession of beats felt by the finger placed over an artery, depends upon the impulse of the left ventricle being communicated along the arterial tube and tlie column of blood which It contains. When a ligature is put upon an artery, no pulse is felt beyond the place where the artery is obstructed, but it is distinct up to that place. This experiment at once shews the dependence of the pulse on the systole of the ventricle, and establishes that this phenomenon is not dependent on the progressive motion of the blood, since, in that part of the artery placed on the side of the ligature next to the heart in which the pulse is distinct, the blood is at rest. Nor does the pulse appear in ordinary circumstances to depend upon lateral distension of the arteries, for such distension occurs to so small a degree as is quite insufficient to account for the produc- tion of the pulse. Arthaud,* a French surgeon, was the first who sustained, in opposition to the opinion prevalent at the time he wrote, the view that the arteries are not laterally di- lated at each systole of the heart, and that the pulse is not to be explained by such dilatation. Arthaud shewed that when an artery is laid bare, no perceptible enlargement of its calibre takes place at the time when the heart con- tracts and the pulse is felt. We have already stated tliat the arterial system being fuller of blood at one time than another must be dilated to admit the blood propelled into the aorta from the ventricle; and it seems to follow from the observations of Arthaud, which have been ably confirmed by the interesting expe- riments of the late Dr. Parry,t that the en- largement of the capacity of the arteries is efliected principally by their elongation. Ac- cording to these experimenters, when one of the larger arteries is laid bare, the eye does not distinguish any lateral enlargement corres- ponding to the systole of the ventricle, and Parry measured with great care the ai'tery at the time of each pulse and between the beats without being able to detect the slightest differences in its size ; but though not percep- tibly distended laterally, the artery undergoes a certain change of place, for at each systole of the ventricle it is propelled in a direction outwards from the heart, and during the di- astole it returns to its former situation. This locomotion of the artery, as it is called, is * Dissert, sur la Dilatation des Arteres. Paris, 1770. t Dr. C. H. Parry’s Inquiry into the Nature of the Arterial Pulse. Hath and Lond. 1816. Dr. Chas. Henry Parry’s .Additional Experiments. Jjond. 1819. obviously produced by the distension and elongation of the larger arteries near the heart. A considerable elongation of the arteries may also easily be seen at all sudden incurvations of these vessels. The bend of the curved part is generally increased and projected further out- wards during the systole; and we observe that a straight part of an artery, if fixed at its opposite ends, is bent at the time of the pulse in conse- quence of its elongation. In many persons in a state of health the arteries may be seen to move under the skin, although not exposed. This motion is generally perceived at places where there is a sudden bend of an artery, or where the artery lies upon an unyielding part, as bone, &c., and in some individuals an ap- pearance of dilatation or lateral enlargement even may be perceived in some of the larger arteries. Although these circumstances shew that the pulse is not attributable to a lateial dilatation of arteries, yet it would appear that such an enlargement does occur in a small degree, for it is occasionally perceptible to the eye in the arteries when laid bare; and M. Poiseuille,* by means of a small apparatus, capable of being applied round a part of an artery, has proved distinctly the occurrence of lateral enlargement, and estimated its extent in the larger arteries at 1-11th of their dia- meter. The finger laid upon an exposed artery does not feel any pulse, unless the artery be com- pressed, and when the arteries are in their na- tural situation covered by the integuments, it is only when they lie upon a hard part, as a bone, and when the sides of the artery are brought nearer to one another by pressure, that the pulse is perceptible. Those instances in which this does not appear to be the case, as well as those in which the dilatation occasionally seems to occur below the integuments, may in like manner depend upon the artery being subjected to pressure of superjacent parts at the place ob- served. It is also sufficiently obvious that the pulse does not depend upon any active change of the artery itself, or upon any vital contraction and dilatation of the vessels,for the exact appear- ance of the living pulse maybe produced in the arteries of a dead animal by injecting water into the arteries with a syringe, if care be taken to imitate with the strokes of the piston the beats of the left ventricle of the heart. A fur- ther proof of this, and an excellent illustration of the nature of the pulse, is obtained from the curious experiment performed by Bichat of connecting the bloodvessels of a living animal with those of a dead one, the result of which is the production of a pulse in the vessels of the dead animal connected with the arteries of the living one. In those instances in which a communication has been established between an artery and a contiguous vein in conse- quence of a wound, or in what is called Aneu- rismal Varix, the vein pulsates exactly like an artery. Many have remarked that the pulse in the * Sur la dilatation des Arteres ; Magendie’s Journ. vol. ix. p. 44; and Breschet’s Repert. 1828.
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