Collection of facts illustrative of the morbid conditions of the pulmonary artery / by Norman Chevers, M.D.

  • Chevers, Norman, 1818-1886.
Date:
1851
Catalogue details

Licence: Public Domain Mark

Credit: Collection of facts illustrative of the morbid conditions of the pulmonary artery / by Norman Chevers, M.D. Source: Wellcome Collection.

Provider: This material has been provided by The University of Glasgow Library. The original may be consulted at The University of Glasgow Library.

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    structure appears to be far less fully de- veloped in the ascending pulmonary artery than in the aorta, and the latter vessel seems to owe its vertical elasticity principally to the tissues which are disposed upon the exterior of its middle coat. As I shall endeavour to shew, it is probably to the rudimentary development of the sub-epithe- lial fibrous tissue in the ascending pulmo- nary artery, that the comparative rarity of semi-cartilaginous and earthy interstitial de- posits in this portion of the arterial tract is due. The question of the comparative size of the pulmonary and aortic orifices has oc- cupied the attention of many anatomists, the results of whose researches have been so greatly at variance as to leave the matter altogether in an undecided position ; one or two authorities declaring that the pulmonary ostium is decidedly narrower than the aor- tic ; while the majority concur in the opi- nion that the former is naturally the vrider of the two. To ascertain the true natural relative size of these two vessels is certainly a matter of no slight difficulty. It will be found comparatively easy to discover the dimen- sions of the aorta, which may be readily measured without producing any extension of its tissues, but it will be seen that to take an accurate measurement of the width of the pulmonary artery, without stretching its thin and yielding coats, is a piece of manipulation which requires considerable tact and caution. It is almost impossible to measure this vessel either by compasses, a rule, or a cylinder, without either allowing it to remain in a partially collapsed state, or producing an amount of dilatation which, of course, does away with the accuracy of the experiment. In measuring the respec- tive width of these vessels in recent sub- jects a fallacy is also liable to arise, from the fact that, under ordinary circumstances, the right cavities and vessels of the heart are, at the moment of death, in a state of extreme distension, while those on the left side are comparatively empty,—under which condi- tions the pulmonary artery is, in a great measure, prevented from undergoing that degree of tonic contraction which is known to occur after death in the whole of the systemic arteries. Lastly, it appears to be certain that, in by far the larger number of individuals, the temporary ob- structions to which the pulmonary cir- culation is always liable, produce a cer- tain degree of permanent dilatation of the artery, which slight dilatation, notwith- standing the exceeding frequency of its oc- currence, the early age at which it is often established, and the unquestionably healthy condition of adjacent parts with which it is generally accompanied, must, in reality, be considered as a decidedly abnormal and mor- bid state. I have taken exact measurements* of four pulmonary arteries selected with the greatest caution from young well-formed adults (three males and one female), whose deaths had been produced by causes not directly influencing the cardiac and pul- monary functions : and in whose lungs and circulatory apparatus no disease could be discovered. In these specimens I found the average measurements of the pulmonary orifice to be as follows :—Circumference— immediately above the valves, 32^ English lines; directly below the valves, 38^ English lines. In eight cases, the average measurement of the upper (and narrowest) portion of the aortic orifice was also within a very small fraction of 32^ lines. The average width of the lower part of the aortic orifice is 36i lines—nearly two lines less than that of the corresponding portion of the pulmonary artery; but it is evident that in measure- ments of this kind, the width of the nar- rowest part of the outlet is the point of most importance, as it alone represents the dimensions of the orifice, by which the blood has exit from the ventricle. The greater width of the lower part of the pulmonary ostium must not be regarded as the effect of .dilatation—it is due to the peculiar form of the right ventricle, which is naturally rather broader at its upper part than the left. From the cau- tion which I employed in choosing these specimens with reference to the stature, age, and cause of death of the indivi- duals-—rejecting many scores of specimens to which more or less objection might have been made on account of the height of the subjects, the causes of dissolution, or the engorged or otherwise faulty state of the lungs—I have no hesitation in stating my conviction that the size of the two arterial outlets of the heart is naturally the same, and that every departure from this corre- spondence must be regarded as a diseased condition. PJ^J^^^ '° ^^i'^'i I l>ave always been in tde habit of measuring the orifices of the large arteries, and which I beUeve to be the least susceptible of error, is to lay the vessel open by a vertical incision, without removing it from the heart, or subjecting it to any rough manipulation, and to place across the part of which it is re- quirett to obtain a measurement, a piece of com- mon twine which has been previously sufficiently wetted to enable it to adhere to the whole inner circumference of the artery : when the string has been accurately applied in a direct line across the vessel, its ends are cut off on either side pre- cisely at the spot where they touch the divided edge of the middle coat of the artery, and the measurement of the portion of string thus sena- rated is immediately taken. This, of course precisely represents the width of the vessel to which it has been applied.