A MILD DEGREE of pulmonary arterial hypertension associated with an increased pulmonary vascular resistance is a normal feature in people livinig at high altitudes.1-4It has been recently demonstrated that a considerable number of museularized pulmonary arterioles is present in these people at all ages.5 This fact gives indeed an anatomic substratum to the hemodynamic findings. The well-known occurrence of right ventricular hypertrophy in adults6 7 and children8 living at high altitudes can now be better understood.In the present paper, the evolution of the elastic configuration of the pulmonary trunk in people native to high altitudes is described.Heath, Wood, DuShane, and Edwards9 have pointed out that in cases of cardiac septal defects associated with pulmonary hypertension,from birth, the "aortic" type of pulmonary trunk could be maintained to the third and fourth decades. When pulmonary hypertension was secondary to an acquired cardiac disease, as in mitral stenosis, the already established "adult" type of pulmonary trunk did not change. Cases of pulmonarv stenosis with pulmonary arterial hypotension exhibited a pulmonary trunk media almost completely devoid of elastic tissue.The evolution of the elastic configuration of the pulmonary trunk at high altitudes strongly suggests that pulmonary hypertension is the determining cause of the differences found in relation to sea level cases.
V ARIATIONS in the thickness of the tunica media of the pulmonary trunk have been reported by Heath, Wood, DuShane, and Edwards,1 both in normal conditions and in response to pulmonary hypertension or hypotension. According to Heath et al., in the newborn the thickness of the media of the pulmonary trunk is the same as that of the aseending aorta. Normally in the course of life the pulmonary trunk increases its medial thickness at a minor ratio than the aorta. Thus, the relation:thickness of the media of the pulmonary trunk over that of the ascending aorta (P/A ratio) which is 1 at birth, falls to 0.6, with a range of 0.4 to 0.8, by the sixth month.These same values are observed for the rest of life.In cases of pulmonary hypertension, either present from birth or secondary to an acquired heart disease, Heath et al. found that the pulmonary trunk exhibited a media as thick as that of the ascending aorta. On the other hand, a pulmonary trunk media of just 0.2 to 0.3 of the thickness of the aortic media was reported by these authors in cases of pulmonary arterial hypotension.The evolution of the thickness of the media of the pulmonary trunk and aseending aorta, from birth to elderly life, in normal people from high altitudes and from sea level, is presented in this paper. This information is intended mainly to complement previous observations on Material and MethodTwo hundred cases were studied. One hundred were persons born and living permanently in places situated between 11,300 to 14,900 feet above sea level. One hundred subjects from Lima (500 feet above sea level) served as control. Both high altitude and sea level cases were selected from previously studied material.2 Selection of these eases was done exclusively on the basis of comparable ages between cases from both groups. The same histologic sections utilized for observations on the elastic structure of the pulmonary trunk and ascending aorta2 were used in the present study.Separation of high altitude cases in two level groups, as in a previous study,2 was not attempted because of the reduced number of cases suitable for measurements of the arterial media in certain ages.The ages of the cases varied from birth to 78 years in the high altitude group and fromi birth to 80 in eases at sea level. According to ages, the cases were distributed in five groups: from birth to 11 months (17 cases at sea level and 17 at high altitudes) ; 1 to 9 years (20 cases at sea level and 20 at high altitudes); 10 to 29 years (25 cases at sea level and 25 at high altitudes) ; 30 to 49 years (22 cases at sea level and 22 at high altitudes); and 50 to 80 years (16 cases at sea level and 16 at high altitudes).Measurements of the thickness of the media of the pulmonary trunk and ascending aorta, were made with the aid of an ocular scale. Those portions of arterial wall exhibiting a fair regularity in thickness were subjected to measurements. Since variations of the thickness of the media in a single pulmonary trunk or ascending aorta, may be frequently observed, a mean value fo...
have pointed out the morphologic characteristics of the elastic tissue in the trunk of the pulmonary artery in cases of congenital and acquired cardiopathies. Among 71 "control" cases that were studied, three types of elastic configuration of the pulmonary trunk were described. According to Heath et al., the presence of long elastic fibers, similar to those seen in the aorta,give the pulmonary artery of the fetus and newborn an "aortic " or " fetal " type of configuration. From the sixth month to the end of the second year the fibers appear fragmented and this characterizes the " transitional" pattern. The scantiness and irregularity of the elastic tissue are the main histologic features of the so-called "adult'" type.We have studied the normal variations of the elastic configuration of the pulmonary trunk in a large series of cases comprising both sexes and of all ages. Some differences from the earlier concepts and facts not previously referred to form the subject of the present report. For the understanding of the changes observed under abnormal conditions it is necessary to be familiar with these earlier concepts and the differences now to be described. The most frequent causes of death were accidents in adults and acute bronchopneumonic processes in children. In the majority of these cases the postmortem studies were performed for medicolegal purposes at the Central Morgue of Lima. Cases from the Loayza Hospital and the Children's Hospital of Lima were also included. Great care was taken to discard cases with cardiac malformations or cardiovascular disease.In 43 cases of the first decade of life the intact hearts were obtained. In these cases, for reasons of a different study,2 the right and left ventricular masses were separated and then the ratio left/ right ventricular weight (Herniann-Wilson index) 3 was obtained. This information has been taken into consideration in the interpretation of results. In the usual histologic preparations the elastic tissue of the media of the pulmonary trunk and the aorta appears in the form of fibers. It actually constitutes sheets or laminae, the sites of "fragmentation" of fibers representing holes or fenestrations of laminae.4 These facts, in the case of the aorta, have been excellently illustrated by Elias.5 Some previous observations were carried out to verify these structural characteristics. In six cases, most of them less than 1 year of age, several cuts in differently oriented planes to the axis of both pulmonary trunk and ascending aorta were made.In every case, the appearance of the elastic tissue, in both arteries, was essentially the same in transverse, longitudinal, and oblique sections. This fact agrees with a lamellar disposition of elastic material in the arterial wall. However, some accentuation in the degree of fenestration of laminae could be frequently noticed in the longitudinal sections. To exclude minor changes ascribed to the plane of sectioning, the samples of arterial wall were always obtained from transversal planes of the anterior wall of the...
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