Theoretical analysis of pressure pulse propagation in arterial vessels.

An original mathematical model of viscous fluid motion in a tapered and distensible tube is presented. The model equations are deduced by assuming a two-dimensional flow and taking into account the nonlinear terms in the fluid motion equations, as well as the nonlinear deformation of the tube wall. One distinctive feature of the model is the formal integration with respect to the radial coordinate of the Navier-Stokes equations by power series expansion. The consequent computational frame allows an easy, accurate evaluation of the effects produced by changing the values of all physical and geometrical tube parameters. The model is employed to study the propagation along an arterial vessel of a pressure pulse produced by a single flow pulse applied at the proximal vessel extremity. In particular, the effects of the natural taper angle of the arterial wall on pulse propagation are investigated. The simulation results show that tapering considerably influences wave attenuation but not wave velocity. The substantially different behavior of pulse propagation, depending upon whether it travels towards the distal extremity or in the opposite direction, is observed: natural tapering causes a continuous increase in the pulse amplitude as it moves towards the distal extremity; on the contrary, the reflected pulse, running in the opposite direction, is greatly damped. For a vessel with physical and geometrical properties similar to those of a canine femoral artery and 0.1 degree taper angle, the forward amplification is about 0.9 m-1 and the backward attenuation is 1.4 m-1, so that the overall tapering effect gives a remarkably damped pressure response. For a natural taper angle of 0.14 degrees the perturbation is almost extinct when the pulse wave returns to the proximal extremity.     

Volume rigidity of the capacitance vessels of rats in local arterial hypotension]

It was shown in experiments on rats that reduction of arterial pressure in the vessels of the posterior extremity for a period of up to three months was accompanied by a decrease of the volume stiffness of the capacitance vessels of this area.     

Patterns of regeneration in vessels of human diseased muscle and skin

Regenerating vessels from 36 muscle biopsies and 12 skin biopsies pertaining to patients with the clinical and histological diagnosis of dermatomyositis-polymyositis and other inflammatory myopathies were described ultrastructurally. The following characteristics of vascular regeneration were encountered: a) alternation of thin and thick endothelial cells, b) superimposed segments of endothelial cytoplasm with formation of twisted intercellular junctions, c) long and complex intraluminal endothelial projections, d) discontinuous and porous perivascular basement lamina or multilaminated basement lamina. Some vessels featured only two or three of the mentioned characteristics. Endothelial fenestrations were occasionally encountered in the skin capillaries and were an exception in the muscle capillaries. In the skin there were aspects suggesting that intercalation of perivascular cells in the regenerating endothelial wall may occur. Most capillaries were in the final stage of regeneration.     

Human tissue-engineered blood vessels for adult arterial revascularization

There is a crucial need for alternatives to native vein or artery for vascular surgery. The clinical efficacy of synthetic, allogeneic or xenogeneic vessels has been limited by thrombosis, rejection, chronic inflammation and poor mechanical properties. Using adult human fibroblasts extracted from skin biopsies harvested from individuals with advanced cardiovascular disease, we constructed tissue-engineered blood vessels (TEBVs) that serve as arterial bypass grafts in long-term animal models. These TEBVs have mechanical properties similar to human blood vessels, without relying upon synthetic or exogenous scaffolding. The TEBVs are antithrombogenic and mechanically stable for 8 months in vivo. Histological analysis showed complete tissue integration and formation of vasa vasorum. The endothelium was confluent and positive for von Willebrand factor. A smooth muscle-specific alpha-actin-positive cell population developed within the TEBV, suggesting regeneration of a vascular media. Electron microscopy showed an endothelial basement membrane, elastogenesis and a complex collagen network. These results indicate that a completely biological and clinically relevant TEBV can be assembled exclusively from an individual's own cells.     

Possibilities and limitations of histomorphometric studies of arterial vessels of the microcirculation

The choice of a procedure for measurements of blood vessels (b.v.) should depend on the type of b.v. investigated: For vessels defined anatomically and in respect to their function of organ supply the method of SUWA et al. (1961) is the most adequate one, provided that b.v. dilatations developing during lifetime and persisting after death as a result of special methods of fixation or shock-freezing or being generated by postmortal perfusion can be excluded. Changes in wall thickness of defined b.v. sectioned transversally can also be determined by measurement of the wall area and/or the maximal chord length. At undefined vessels procedures which measure the wall-to-lumen ratio are useless, because lumen changes are not quantifiable. Thus lumen changes can mask of mimick changes in wall thickness. The especially interesting b.v. either with a pathologically changed or without an elastic membrane are not measurable. The unsable method to detect changes in wall thickness at undefined b.v. is founded on the determination of the vessel wall area and/or the number of all the b.v. classified according to their diameter of a certain organ region. But the investigation of the smallest precapillary vessels presupposes their visualization by a special modification of the ATPase reaction.     

Determination of arterial wall thickness variations of vessels in the microcirculation by the ATPase-Quantimet method

The use of the Quantimet for measurements of structural wall reactions of blood vessels (b.v.), visualized selectively by a modification of the ATPase reaction, requires that changes in wall thickness are not mimicked by differences in deposition of the reaction product, by changes of the b.v. lumen, and/or by b.v. elongations, especially meanderings occurring independently of thickenings of vessel walls and caused solely by increase of the intravascular pressure or by vasoconstriction. The article has substantiated the conclusion that these requirements are fulfilled.     

The neurogenic component of the tone of capacitance vessels in regional arterial hypotension]

It was shown in experiments on rats that lowering of the volume stiffness of the capacitance vessels in the area of the chronic regional arterial hypotension occurred only after their denervation. Experiments on the innervated hind limb showed that the volume stiffness of the capacitance vessels in the area of hypotension failed to differ from the corresponsing indices in control rats.     

Estrogen modulates the mechanical homeostasis of mouse arterial vessels through nitric oxide

We have recently shown that estrogen causes vessel dilation through receptor-mediated stimulation of nitric oxide (NO) production. Here, we hypothesize that estrogen modulates the mechanical homeostasis in the blood vessel wall through NO production. The mechanical properties of female ovariectomized (ovx) mice, female mice lacking the gene for endothelial NO synthase (eNOS(-/-)), and control female and male mice were studied to test the hypothesis. The femoral and carotid arteries and aorta were cannulated in situ and mechanically distended. The stress, strain, elastic modulus, and wall thickness of vessels in ovx and eNOS(-/-) mice, as well as intact female and male mice, were determined. Western blot and immunohistochemistry were used to assess eNOS protein expression in the aorta. Moreover, NO by-products of the femoral and carotid artery were determined by measuring the levels of nitrite and nitrate. Our results show that ovariectomy and eNOS(-/-) significantly decrease the strain in all arteries. Furthermore, the eNOS protein was significantly reduced in ovx mice. Finally, the NO metabolites were significantly decreased both in ovx and eNOS(-/-) mice. We found statistically significant correlations between the structural (wall thickness), mechanical (stress, strain, and elastic modulus), and biochemical parameters (NO by-products). These novel results connect NO to the structural and mechanical properties of the vessel wall. Hence, the effect of endogenous estrogen on the arterial mechanical properties is mediated by the regulation of NO derived from eNOS.     

Thyroid status and response to endothelin-1 in rat arterial vessels

We have previously reported that changes in thyroid status are associated with significant alterations in skeletal muscle blood flow during exercise and that changes in endothelium-dependent vasodilation may contribute to these blood flow abnormalities. The purpose of this study was to test the hypothesis that altered endothelium-dependent vasoconstriction is also associated with changes in thyroid status. To test this hypothesis, rats were rendered hypothyroid with propylthiouracil (Hypo, n = 14) or hyperthyroid with triiodothyronine (Hyper, n = 14) over approximately 3 mo. Treatment efficacy was confirmed by altered (P < 0.05) citrate synthase activity in several hindlimb skeletal muscles from Hypo and Hyper, compared with that in muscles from euthyroid rats (Eut, n = 12). Vascular rings were prepared from abdominal aortae, and responses to several vasoactive agents were determined in vitro. As found previously, maximal acetylcholine-induced vasorelaxation was modulated by thyroid status (Eut, 47 +/- 9; Hypo, 28 +/- 6; Hyper, 68 +/- 5%; P < 0.05). Contractile responses of vascular rings with intact endothelium to the endothelium-derived constrictor endothelin-1 (ET-1), however, were similar among groups across a range of ET-1 concentrations. In addition, maximal responses [Eut, 3.75 +/- 0.47; Hypo, 2.72 +/- 0.25; Hyper, 3.22 +/- 0.42 g; not significant (NS)] and sensitivities (Eut, 8.12 +/- 0.09; Hypo, 8.10 +/- 0.06; Hyper, 8.28 +/- 0.09 -log M; NS) to ET-1 were similar among groups. If these findings from the conduit-type abdominal aorta extend into resistance vasculature, it appears that changes in endothelium-dependent vasoconstriction do not contribute to skeletal muscle blood flow abnormalities associated with thyroid disease states.     

Patterns of pollen dispersal in a small population of the Canarian endemic palm (Phoenix canariensis)

The genetic diversity of small populations is greatly influenced by local dispersal patterns and genetic connectivity among populations, with pollen dispersal being the major component of gene flow in many plants species. Patterns of pollen dispersal, mating system parameters and spatial genetic structure were investigated in a small isolated population of the emblematic palm Phoenix canariensis in Gran Canaria island (Canary Islands). All adult palms present in the study population (n=182), as well as 616 seeds collected from 22 female palms, were mapped and genotyped at 8 microsatellite loci. Mating system analysis revealed an average of 5.8 effective pollen donors (N_ep) per female. There was strong variation in correlated paternity rates across maternal progenies (ranging from null to 0.9) that could not be explained by the location and density of local males around focal females. Paternity analysis revealed a mean effective pollen dispersal distance of ∼71 m, with ∼70% of effective pollen originating from a distance of <75 m, and 90% from <200 m. A spatially explicit mating model indicated a leptokurtic pollen dispersal kernel, significant pollen immigration (12%) from external palm groves and a directional pollen dispersal pattern that seems consistent with local altitudinal air movement. No evidence of inbreeding or genetic diversity erosion was found, but spatial genetic structure was detected in the small palm population. Overall, the results suggest substantial pollen dispersal over the studied population, genetic connectivity among different palm groves and some resilience to neutral genetic erosion and subsequently to fragmentation.     

Architecture of the media of the arterial vessels in the dog brain: A scanning electron-microscopic study

Summary The architecture of the media of arterial vessels in dog brain was investigated using scanning electron microscopy. The arrangement and shape of the circularly-oriented smooth muscle cells varied with vessel diameter: The arteries (>100 m in diameter) had 4–10 layers of spindle-shaped smooth muscle cells; the muscular arterioles (30–100 m), 2–3 layers of spindle-shaped smooth muscle cells; the terminal arterioles (10–30 m), a compact layer of spindle-shaped smooth muscle cells with more dominant nodular or rod-like processes and thin lateral processes; and the precapillary arterioles (5–15 m), a less compact layer of branched smooth muscle cells.Longitudinally-oriented muscles were observed in the medio-adventitial border. The distribution and arrangement of these muscles varied with vessel size: in the large arteries (> 300 m in diameter), at the branching sites only; in the small arteries (100–300 m), at both the branching and non-branching sites; in the muscular arterioles, at both the branching and non-branching sites in a reticular arrangement with some muscle cells having an asteroid appearance; in the terminal aterioles, only asteroid-like muscle cells were found at the branching and non-branching sites.     

Adrenergic responses of arterial and venous vessels in the cat skeletal muscle in hypoxia and hypothermia

In 12 anesthetized cats both hypoxia and hypothermia enhanced the shifts in arterial resistance against blood flow in response to noradrenaline and diminished the shifts in response to isoproterenol. Combination of both stress factors considerably weakened the adrenergic vasoconstriction and rather little affected the adrenergic vasodilatation. The findings suggest that protective effect of hypothermia against the background of a hypoxic stress might be a mechanism preventing disorders in the tissue metabolism.     

Morphological aspects of age-related adaptation of the arterial vessels of the human kidneys in various cardiovascular diseases

The investigation has been performed in 190 normal kidneys and at certain cardiovascular diseases (atherosclerosis of the abdominal aorta, hypertension, chronic ischemic cardiac disease and their combination). Principally similar morphological structures are mobilized in the process of the renal arterial bed adaptation both normal and at the cardio-vascular diseases studied. Transition from certain functional changes to the organic ones in the muscular tunic and in the elastic membranes of large arteries, in correlation of afferent and deferent glomerular arterioles of all cortical layers is stated, as well as adaptive rearrangement of the microvessels and of the juxtamedullary shunt.