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Biomedical subjects

M Zamir

Publications and source records attributed to M Zamir.

At least 37 records · Page 2Linked to original sources
PubMed1988

Roots and calibers of the human coronary arteries.

The anatomical structure of the coronary-aortic junctions in humans is studied by using corrosion casts of the coronary network. A model is proposed for the specification of these junctions in terms of vessel diameters and branching angles, and the model is used to produce morphological data on these junctions which hitherto have not been available. This anatomical model correlates poorly with the accepted theoretical model of arterial bifurcations in the cardiovascular system. The results suggest that the structure of the coronary-aortic junctions is very different from the structure of typical arterial bifurcations and, by implication, that the flow conditions under which they function are very different. A good understanding of these junctions is important in coronary bypass surgery, where the coronary-aortic junctions are emulated by creating a new anastomosis for the graft at the base of the ascending aorta, and in coronary artery disease, where atherosclerotic lesions occur not far from the coronary-aortic junctions.

Aorta↗
PubMed1988

Network analysis of an arterial tree.

The arterial tree of a Sprague-Dawley rat was casted and carefully mapped with the aim of comparing its network characteristics with those suggested by the classical model of an arterial tree. It is shown that if the tree is to be measured accurately, the concept of 'whole vessels' on which the classical model is based must be abandoned since such vessels do not actually exist in the network, nor can they be accurately defined. The concept of 'vessel segments' is proposed instead and its use is demonstrated. A total of 1313 vessel segments in the arterial tree of the rat are mapped and divided into well defined 'levels'. The length and diameter of each segment are measured and the distribution and averages of these at different levels are presented as indicators of the branching characteristics of the tree.

Animals↗
PubMed1988

Distributing and delivering vessels of the human heart.

The branching characteristics of the right coronary artery, acute marginal, posterior descending, left anterior descending, circumflex, and obtuse marginal arteries are compared with those of diagonal branches, left and right ventricular branches, septal, and higher-order branches, to test a newly proposed functional classification of the coronary arteries in which the first group rank as distributing vessels and the second as delivering vessels. According to this classification, the function of the first type is merely to convey blood to the borders of myocardial zones, while the function of the second is to implement the actual delivery of blood into these zones. This functional difference is important in the hemodynamic analysis of coronary heart disease, as it provides an assessment of the role of a vessel within the coronary network and hence an assessment of the functional importance of that vessel in a particular heart. Measurements from casts of human coronary arteries are used to examine the relevant characteristics of these vessels and hence to test the basis of this classification.

Arteries↗
PubMed1987

Morphometric analysis of the distributing vessels of the kidney.

Branching angles and branch diameters of the distributing vessels in the renal networks of rats were measured and the results are compared with data reported previously from the coronary network of the same species. Comparison is also made with what is known to be optimum on theoretical grounds to determine to what extent the branching characteristics of the renal network are governed by considerations of optimality, and to what extent they are affected by other considerations, relating particularly to the role that the network plays in the blood processing function of the kidney.

Animals↗
PubMed1987

Segment analysis of human coronary arteries.

Detailed measurements of vessel lengths and diameters from the coronary network of the human heart are presented. To allow accurate definition of length and diameter, the measurements were made in terms of vessel segments rather than whole vessels. A vessel segment was defined to be the interval between two consecutive branching sites. The results provide the first quantitative description of the coronary network. The new concept of vessel segment and the method of analysis are proposed as a means for an accurate description of the branching characteristics of the coronary network, comparing the network with others in the cardiovascular system and comparing the vasculature in the normal versus that in the diseased heart.

Coronary Vessels↗
PubMed1986

Cost analysis of arterial branching in the cardiovascular systems of man and animals.

A new scheme is presented whereby data on arterial branching can be interpreted in terms of direct cost to the physiological system. The scheme makes it possible to assess, at a glance, the true degree of optimality of an arterial network. Departure from optimality is indicated in terms of cost, rather than in terms of the difference between theoretical and measured branching angles. The scheme is applied to several groups of biological data and new conclusions are reached with regard to their degrees of optimality.

Animals↗
PubMed1986

Branching characteristics of human coronary arteries.

Branching angles and branch diameters were measured in a total of 850 arterial junctions in the coronary networks of two human hearts. Comparison is made with similar data obtained previously from the coronary networks of rats, and with what is considered to be optimum on theoretical grounds. It is concluded that the branching characteristics of the human coronary arteries are closer to the theoretical optimum than those of the coronary networks of rats. While the human data exhibit some departure from optimality and a good amount of scatter, these are well within levels observed elsewhere in the cardiovascular systems of man and animals, and considerably better than those found in the coronary networks of rats. The departure from optimality, in terms of physiological cost to the system, is within 5% for most data points.

Animals↗
PubMed1985

Vasculature in the walls of human coronary arteries.

Casts were produced of the arterial networks of 25 human hearts obtained at autopsy from subjects who were not diagnosed as having cardiovascular disease. Many casts showed imprints of atherosclerotic plaques, remnants of calcified masses, and fine vascular meshes near the lumen of the major coronary arteries. Of 25 casts produced, 14 contained one or more of these anomalies, seven contained vascular meshes, and five of these related to imprints and/or calcified masses. Analysis of these findings in the context of atherosclerosis, intramural hemorrhage, and vascular spasm, suggests possible relationships between them. The findings support the hypothesis that neovasculature in the walls of coronary arteries may play a role in the pathogenesis of vascular disease and malfunction.

Adult↗
PubMed1984

Cost of departure from optimality in arterial branching.

Measurements of branching angles in the arterial tree have in the past indicated a great deal of scatter away from what is expected to be optimum on theoretical grounds. In this study the cost penalty of nonoptimum branching angles is calculated for the first time to determine how far from optimum these angles are. The results lead to the remarkable conclusion that while the scatter of the measured branching angles is fairly large, they represent deviations from optimum angles which correspond to only 2% or so penalty in cost.

Arteries↗
PubMed1984

Branching characteristics of coronary arteries in rats.

The purpose of this study is to examine quantitatively the branching characteristics of the coronary arteries. Branching angles and vessel diameters were measured in a total of 175 arterial bifurcations in the coronary beds of rats, and the results are compared with those of 350 bifurcations in other parts of the cardiovascular system of the same species. Significant differences are found in the values of branch diameters and branching angles, both being found generally lower in the coronary bed than in other parts of the system. On statistical grounds these differences are found to have very high significance levels, with P values less than 0.02 in the case of branching angles and much less than 0.001 in the case of branch diameters. On physiological grounds, the differences are such as to place the coronary arteries further away from the "theoretical optimum" than are vessels in other parts of the cardiovascular system. The theoretical optimum represents branching angles and branch diameters which make arterial bifurcations more efficient physiologically.

Animals↗
PubMed1984

Pressure rise at arterial bifurcations.

The increase in cross-sectional area within an arterial bifurcation is shown to be much larger than that predicted by the conventional area ratio beta. Modified area ratios which better describe this increase are presented and their values are assessed both from theoretical considerations and from physiological data. The results suggest that the pressure rise within an arterial bifurcation may be much more severe than that suggested by the conventional area ratio beta, and that local flow separation may be far more common. These conditions may adversely affect endothelial tissue and orderly flow within the bifurcation region.

Animals↗
PubMed1983

Internal geometry of arterial bifurcations.

The internal geometries of 137 arterial bifurcations were measured, using enlarged angiographic pictures, to determine the position of the apex of each bifurcation in relation to the ostium of the parent artery. The measurements, relating to different parts of the cardiovascular system of man and some to that of rabbit and pig, were compared with each other and with a theoretical model of an 'optimum' arterial bifurcation. The results were found to be consistent with a position of the apex which is optimum from the point of view of local hemodynamics. In that position, the apex lies on a straight dividing streamline which divides the flow in the parent artery in the proportion required by the two branches.

Animals↗
PubMed1983

Arterial bifurcations in the cardiovascular system of a rat.

Arterial bifurcations in the cardiovascular system of a rat were studied, using a resin cast of the entire arterial tree. At each bifurcation, measurements were made of the diameters of the three vessels involved, the two branching angles, and the angle delta, which the parent artery makes with the plane containing the two branches. The results were found to be consistent with those reported previously in man and monkey. In addition, measurements of delta in the present study indicate that arterial bifurcations are mostly two dimensional.

Animals↗
PubMed1982

Arterial branching in various parts of the cardiovascular system.

Angiographic pictures of vascular beds in various parts of the cardiovascular system were analyzed to study the geometrical structure of arterial bifurcations. The sites of arterial bifurcations were enlarged individually, and measurements were made of the branching angles and branch diameters at each site. Results from various parts of the cardiovascular system of man, and some from rabbit and pig, were compared with each other. The measurements were also compared with "optimum" values of branching angles and branch diameters which have been predicted by various theoretical studies. In general the measurements were found to give support to the theoretical premise that branching angles and branch diameters in the cardiovascular system are dictated by certain optimality principles which aim to maximize the efficiency of the system in its fluid-conducting function. In some parts of the system, however, the measured angles and diameters were found to be decidedly lower than those predicted by theory.

Animals↗
PubMed1982

Arterial branching in man and monkey.

Vessel diameters and branching angles are measured from a large number of arterial bifurcations in the retina of a normal human subject and in that of a rhesus monkey. The results are compared with each other and with theoretical results on this subject.

Animals↗