Lengths and Diameters of Peripheral Arterial Vessels in the Living Animal

Transcription

1 Lengths and Diameters of Peripheral Arterial Vessels in the Living Animal By Mary P. Wiedeman, Ph.D. In 1888, a histological study Avas made of blood vessels in dog mesentery by Mall. 1 Several decades later, the data were used by Schleier 2 to discuss the effects of branching of an arterial tree on the velocity and pressure of blood. Mall's data were again used by Green, 3 in 1944, to compute the approximate dimensions, numbers, lengths, and total crosssectional area of component parts of the circulation. No data, such as Mall's, were available from the living animal. It seemed that significant differences might be found in diameters and lengths of vessels in living material when compared to similar measurements in fixed material. Measurements of a major arterial vessel, and its ramifications down to the capillary nets, have been carried out in living animals. The site for microscopic observation was the subcutaneous area of the bat's wing. The length and inside diameter of an artery were measured, as were the branches from the artery, referred to here as small arteries. The branches of the small arteries, designated arterioles, were measured for length and diameter, and similar measurements were made of the arteriolar branches, the capillaries. From the data, the cross-sectional area of the individual vessels and the total cross-sectional areas of the vascular nets formed by the small arteries, arterioles, and capillaries were calculated. Comparisons of the values thus obtained are made with similar values from Schleier, 2 and from Green, 3 both of whom used Mall's 1 measurements on the fixed mesenteric vessels in the dog. From the Physiology Department, Temple University, School of Medicine, Philadelphin, Pennsylvania. This investigation was supported in part by Research Grant H-2880 (Co) from the National Heart Institute, TJ. S. Public Health Service. Received for publication November 8, Methods Common brown bats (Myotis) were prepared for observation by placing an unanesthetized animal in a, holder and extending' one wing over a glass plate. A drop or two of mineral oil was put between the wing and the glass plate and also on the upper surface of the wing for increased visual clarity. The artery and its branches selected for measurement are shown enclosed by the dotted line in figure 1. A suitable eyepiece micrometer was used to measure the length and the inside diameter of the vessels. A magnification of 400 X was used when measuring the larger vessels and a magnification of 1,200 X was used for the arterioles and capillaries. The length of the major artery was measured from its origin to its first bifurcation. A small artery was considered to end at the point where its forward flow was stopped by blood flowing from the opposite direction. Such a condition occurred where two small arteries, originating either from adjacent arteries or from the same artery, met to form an arcade. Bifurcating branches of the major artery, as well as some arterioles, also terminated in the formation of arcades. Various types of arcades are shown in figure 2. Arterioles, the branches from the small arteries, ended by branching to form a capillary net or by forming an arcade. Capillaries arose as side brandies from the arterioles. The end of an arterial capillary was considered to be the point where an inflowing tributary, or venule, joined the vessel being measured. Results The average length of eight major arteries was found to be 17.0 mm. and the average diameter was 52.6 p.. An average number of 12.3 small arteries originated from this vessel. No correlation was found between the length of the vessel and the number of branches which arose from it. The cross-sectional area of each artery Avas calculated and the average cross-sectional area was found to be 2,263.3 sq. p. The average length of 25 small arteries was found to be 3.5 mm. with an average diameter of 19.0 /x. The small arteries gave Circulation Research, Volume X, April 19G2

2 PERIPHERAL ARTERIAL VESSELS 687 MAIN ARTEf t r FIGURE 2 Various types of arterial arcades. FIGURE 1 Area in the bat wing used for measurements, of a major arterial vessel and its ramifications. rise to an average number of 9.7 branches, the arterioles. An average of the individual cross-sectional area of small arteries was found to be sq. /x and the total crosssectional area of these vessels was calculated to be 4,144.5 sq. J X. The average values for arterioles, based on measurements in 15 vessels, were 0.95 mm. for length, 7.0 JX for diameter, and 42.7 sq. JX for individual cross-sectional area with a total cross-sectional area for the vessels of 5,101.2 sq. jx. Arterioles gave rise to an average number of 4.6 capillaries. The average values for the capillaries, based on measurements of 24 vessels, showed the length to be 0.23 mm. and the diameter to average 3.7 p.. The individual cross-sectional area was 11.7 sq. /X, while the total cross-sectional area was 6,548.1 sq. JX. The relationships between the lengths and diameters of the vessels can be seen in figure 3. The arterioles are roughly twice the diameter of the capillaries and almost one-half the diameter of the small arteries. The small arteries are less than one-half the diameter of their parent vessel. Comparison with the diameters of similar vessels, reported by Schleier, 2 show a different relationship. The arterioles have a diameter roughly three times that of the capillaries and are many times smaller than the terminal branches from which they arise (see fig. 4). The total cross-sectional areas produced by division of the vessels in the various portions of the arterial bed of the bat wing show a linear increment from artery to capillary (see fig. 5). These values differ greatly from those obtained when Mall's 1 data were used for computation by Schleier, 2 and by Green? There is a very small increment in total crosssectional area between artery and small arteries, a slightly larger increase in area between small arteries and arterioles, and a very marked increase in area between arterioles and capillaries. It is very likely that the measurements on fixed sections of the dog mesenteric vessels included many more capillary vessels than were counted in the living bat wing. The tremendous number of capillary vessels reported for the dog mesentery would be a possible result if the termination of arterial capillaries could not be established due to the absence of blood flow. The great difference in the number of vessels reported for the various types results in a wide variance in the calculated total cross-sectional area. A comparison of the calculated total crosssectional areas from Schleier, 2 and from Green, 3 and from the bat wing at the level

3 688 WIEDEMAN r\ FIGURE 3 Lengths and diameters of various arterial blood vessels in the living bat. i- UJ Z FIGURE 4 Comparison of the diameters of blood vessels in the living bat (MPW) and fixed tissues in the dog (JS). of the artery, small arteries, arterioles, and capillaries is shown in figure 6. Discussion It was an expected finding that the actual values of length and diameter of the various arterial vessels would be different in the bat wing and the dog mesentery. However, it is the disagreement in the relationship between the vessels that is of importance. The basis of the disagreement is certainly to be found in the difference between measurements made in the fixed preparation and the living animal. There are many difficulties associated with

4 PERIPHERAL ARTERIAL VESSELS 689 FIGURE 5 Increase in total cross-sectional area from artery to capillary. Comparative lengths of the vessels are also shown. TOTAL CROSS-SECTIONAL AREA 2 < g = < o FIGURE 6 Comparison of computed total cross-sectional areas from the living bat (MPW), from Schleier (JS), and from Green (HDG), who used Mall's measurements on fixed mesenterie vessels in the dog. Circulation Hcsaarch, Volume X, April 1962

5 690 WIEDEMAN measuring vessels in a fixed preparation, for there is undoubtedly much distortion in the size of vessels subjected to histological preparation. A further difficulty is the inability to classify accurately a vessel in which there is no blood flow. It is also reasonable to assume that the figures given by Schleier, 2 and by Green, 3 for the numbers of small arteries, arterioles, and uapillai-ies in the fixed preparation are hardly more than a rough estimate. However, this value is important in calculating the total cross-sectional areas formed by these vessels. The selection of the subcutaneous area of the bat's wing as a representative site for vascular measurements may provoke criticism. In defense, the vascular pattern seen in the bat wing is comparable to subcutaneous beds described in other animals. Actually, the pattern is a familiar one, being very similar to vascular beds seen in a variety of tissues. Also, it is possible to follow blood flow in this preparation in its complete circuit from distributing artery to collecting vein. Green 3 has pointed out that his data obtained from computing the dimensions, numbers, lengths, and total cross-sectional area of the component parts of the circulation from Mall's 1 original work on the dog's mesenteric vessels are very rough, since many assumptions were necessary. The values reported here are the result of direct microscopic observation in living tissue. Assumptions are limited to the use of average values obtained from a large sample. Summary Measurements of the length, diameter, and number of branches of arterial vessels were made from a distributing artery to the capillaries in a living bat. From the values so obtained, cross-sectional areas in various portions of the arterial bed were calculated. An almost linear decrease in the diameters of successively smaller vessels was found. There was also a linear relationship in the calculated total cross-sectional areas formed by the various vessels. The results are not in agreement with similar reports made by others using measurements from vessels in a fixed preparation. References 1. MALL, F.: Die Blut und Lymphwege im Dunndarm des Hundcs. In Koniglich Sachsschen Gesellschaft der Wissenschaft. Abhandlungen der Mathematisch-physischen Classe. Vol. XIV, SOHLEIEE, J.: Der Energievebriuich in der Blutbahn. Arch. ges. physiol. 173: 172, GKEEN, H. D.: Circulation; physical principles. In Medical Physics, edited by 0. Glasser. Chicago, Tear Book Publishers, 1944.