No abstract

The diameter, area, and volume of individual human erythrocytes (of 8 subjects, newborn to age 71) were determined by photographing the cells hanging on edge. Measurements from high magnification prints were processed by computer. The distributions of diameter, area, and volume are described statistically, with the unexpectedly linear regression equations for their interrelations. The plot of area vs. volume for the 1016 normal cells from seven subjects (newborn excluded) was remarkably linear with a "straight-line" boundary restricting the distribution. Shape was characterized by a dimensionless "sphericity index" (4.84.volume 2/3 /area). Cells of larger volume tended to be thinner than the smaller cells. The red cell can easily be deformed at constant volume, but an increase in membrane area results in hemolysis. A theoretical geometric parameter, the "minimum cylindrical diameter" (MCDiam), in microns, the thinnest cylindrical channel through which each individual cell could pass, predicts the linear boundary of the plot of area vs. volume. The MCDiam value of 3.66 µ ± 0.04 SEM accurately represents the thinnest channel through which 95% of the cells can pass. In two splenectomized patients with hereditary spherocytosis the MCDiam was increased to approximately 4.0 µ, suggesting that the severest restriction is located in the spleen.

Measurements on the directional organization of collagen are necessary for relating the structure and mechanical function of blood vessels. The birefringent optical property of collagen has enabled us to assess the collagen architecture for brain arteries, which are prone to spasm and aneurysm formation. Using the universal stage and polarizing microscope, we measured the three-dimensional organization of the collagen of the main layers of the artery wall, and examined the effect of distending pressure on that organization. Adult arteries obtained from autopsy were fixed at one of three distending pressures, 30, 120 and 200 mm Hg; they were embedded in paraffin and sectioned parallel to the vessel axis at 4 µm thickness. Sections were stained with picrosirius red, a birefringent enhancement stain specific for collagen. Orientation data were obtained from tangential sections from thirteen arteries. We chose to use tangential sections that graze the curving surface of individual layers, to permit measurements that are equally sensitive to fibres in the mechanically meaningful range of directions including longitudinal, helical and circumferential. Each measurement was from a single fibre or group of fibres at a specific location; the mean direction and its variation of alignment within each artery layer were calculated. In some arteries, the adventitia and subendothelium measurements were separated into sublayers, distinguishable by the birefringent optical appearance. Main findings included a substantial component of longitudinal fibres in the adventitia and subendothelium, highly varied in coherence and mean direction, and a thin collagen layer of the adventitia, radially outside the medial muscle cells, that was highly organized circumferentially (circular standard deviation of 9°). At higher pressures, the collagen fabric of all the layers was increasingly coherent and more circumferential in direction.

With the long term goal of improving our understanding of the mechanisms involved in coronary artery spasm, we have undertaken a two part study of the artery structure. We have made a comparison of the relative proportions of the different layers in proximal and distal regions of the main coronary arteries, and have quantitatively assessed their three dimensional structural fabric. Major coronary arteries from nine hearts were prepared for histological examination after fixation at a transmural pressure of 120 mm Hg. Measurements from 14 proximal and distal pairs of the cross sectioned arteries showed a dominant subendothelial layer, which diminished in thickness distally, with a small fraction of muscle cells interspersed with collagen. Three dimensional orientation measurements of the collagen and muscle components, which are birefringent, were obtained from one pair of segments from each of the left anterior descending, circumflex and right coronary arteries, using the polarising light microscope and Universal stage. Findings showed (1) a single circumferential order of adventitial collagen, with a mean circular standard deviation (CSD) of 22.3 degrees; (2) very highly ordered medial smooth muscle, mean CSD of 5.0 degrees (both findings are quantitatively similar between proximal and distal segments of artery, and between arteries); and (3) a multilayered fabric of collagen in the subendothelium in all vessel segments. The principal contributor to functional differences between proximal and distal regions may be the prominent and structurally varied subendothelial layer of the coronary arteries.

No abstract

Background and Purpose-Unruptured saccular aneurysms are relatively common, occurring in 4% to 9% of autopsies.Their development at the apex region of brain artery bifurcations is attributed to a combination of structural factors and the effect of blood pressure. Collagen is a primary tension-bearing fabric of the vessel wall, and our purpose was to examine its 3-dimensional alignment at arterial branches. Methods-Sixteen segments of arteries from the circle of Willis, including bifurcations, were pressure distended, fixed, and sectioned in 1 of 3 orthogonal planes. We measured the 3-dimensional organization of collagen at the flow divider by using the polarized light microscope. An electron microscopy study performed in tandem provided measurements on the collagen fibril diameters and packing density. Results-Orientation data of the collagen fabric were obtained from sections from 3 different cutting planes. The tunica media of all bifurcations had an alignment that was primarily circumferential, and the medial gap (medial defect) was distinguishable at the apex of all bifurcations. The subendothelial layer was thin at the apex but thicker and more disorganized distally. Adventitial collagen showed little organization except for a high degree of alignment along the apex. Results from the electron microscopy study showed densely packed collagen fibrils of uniform diameter at the apex, compared with slightly smaller and less densely packed fibrils nearby. Conclusions-In the region of the medial gap, a narrow band of highly aligned tendonlike collagen running in the direction of the ridge of the flow divider was a consistent finding. This structure would provide strength and stability to the vessel and is inconsistent with the concept of an inherent defect in the structure of bifurcations. (Stroke. 1998;29:1595-1601.)

No abstract

The aneurysm wall, which must withstand arterial blood pressure, is composed of layered collagen. Wall strength is related to both collagen fiber strength and orientation. When the aneurysm enlarges, the amount and organization of the collagen fibers change, potentially increasing the risk of rupture. We studied the directional organization and molecular strength of the collagen fibers layer by layer across the walls of four aneurysms in order to measure their mechanical integrity. The technique incorporates the birefringent properties of collagen, enabling us to use linearly polarized light for measuring the orientation of the fibers, and the Sénarmont compensator to measure the birefringence and thus mechanical strength. Intact aneurysms were obtained at autopsy, fixed at physiological pressure, sectioned at 4 microm, and stained with 0.05% picrosirius red. By combining birefringence and orientation data we estimated tensile strength as a function of direction on the aneurysmal wall. The average breaking strength of the wall ranged from 0.73 to 1.9 MPa. Comparing the weakest to the strongest direction, the breaking strength varied by a factor of up to 2X, implying a significant degree of mechanical anisotropy.