International journal of microcirculation, clinical and experimental最新文献

The spatial pattern of capillaries is one of many factors important for the optimisation of oxygen and nutrient delivery in a specified region of tissue. One area of particular interest to the vascular specialist is the skin of the dorsum of the foot and toes, as these are especially prone to ulceration in patients with arterial disease. The aim of this study was therefore to establish the extent of capillary density (CD) heterogeneity in the normal skin of the dorsum of the foot and toes, since any great non-uniformity might produce regions of low perfusion, which may become vulnerable to ulceration. Using white-light (native) videomicroscopy at a magnification of x 40 in 15 healthy subjects (mean age 72 years), the dorsum of the foot and toes was systematically mapped by determining the CD at each of 25 sites on the dorsum of the foot, and at 2 sites on the distal phalanx of each toe. Off-line analysis of videoprints was then undertaken to determine CD at each site, according to a fixed protocol of measurement and data analysis. The mean value and spatial coefficient of variation of CD was then calculated for each foot. There was striking spatial heterogeneity of CD in the dorsum of the foot, some areas having low numbers of capillaries and other areas in the same foot having higher capillary numbers. This spatial heterogeneity of CD was observed in all the feet studied, and the mean coefficient of variability was 22.3%. The toes had a significantly higher mean CD (47.7/mm2) than the dorsum of the foot (33.5/mm2, p < 0.001). The finding of a significant spatial heterogeneity of CD in the foot of normal subjects has important implications in relation to function, methodology of CD measurement and the possibility that regional 'rarefaction' of CD may contribute to the pathogenesis of skin ulceration in arterial disease.

The long-term behavior of an arterial autograft was studied with special attention to the evolution of intimal hyperplasia. An arterial autograft measuring approximately 5 mm in length was implanted in the right common iliac artery of female Sprague-Dawley rats. Animals were sacrificed at 90, 120, 150, 180, 240, 360, 400, 540 and 730 days after implantation. Grafts were evaluated by optical microscopy, electron microscopy, and morphometry. Myointimal cells were marked using an antiactin monoclonal antibody and studied by transmission electron microscopy. In the long term, the myointima of the arterial wall appeared as a consolidated layer formed by smooth muscle cells of contractile phenotype, abundant extracellular material consisting of clumps of elastin and collagen fibers. Cell maturity and degree of differentiation were demonstrated by the incorporation of antiactin antibody. The medial layer of the grafted segment suffered a marked long-term loss of cells and became an acellular layer sustained by the elastic layers. The adventitial layer was markedly cellular and had abundant vasa vasorum. Morphometry showed that the myointimal layer in the operated territory was not uniform and consisted of tongues of varying thickness. The total thickness of the arterial wall did not differ significantly (p > 0.05) between the graft and the proximal and distal areas. The results suggest that the intimal hyperplasia originating during the repair process could assume some functions of the degenerated medial layer, maintaining long-term vascular homeostasis.

Microangiopathy of the skin has been recognized as an important factor in the development of skin diseases connected with chronic venous insufficiency (CVI). Here the relationship between postcapillary transmural pressure and precapillary vaso-constriction - we call it the postural feedback system - was examined in venous ulcers (n = 12) and compared to blood flow regulation in the inner ankle area of healthy controls (n = 12). Blood flow changes were measured by laser Doppler fluxmetry. Changes in the laser Doppler flux (LDF) minus the biological zero value were measured after 3 min of arterial occlusion, during 3 min of venous occlusion, while the leg was elevated and while it was lowered and expressed relative to the pretest resting value. In venous ulcers the LDF remained nearly unchanged after arterial occlusion (3 vs. 190%, p < 0.001), leg elevation caused an LDF decrease contrary to what was seen in the controls (-17 vs. +80%, p < 0.001), in the lowered leg an LDF decrease was found (-51 vs. -65%) and venous occlusion led to a profound reduction of flux (-78 vs. -84%). In severe CVI the precapillary arterioles seem to be dilated even with the leg at heart level. This finding means that the postural feedback system under resting conditions is upregulated, and 'luxus' hyperperfusion results. The upregulated postural feedback system contributes to the cutaneous microangiopathy due to chronic venous congestion.

To better understand normal microvascular network growth, we conducted a longitudinal study on the spinotrapezius muscle of Sprague-Dawley rats of 3 ages: weanling (3-4 weeks), juvenile (7-8 weeks) and mature (11-12 weeks). Morphometric analysis revealed that despite dramatic growth of the muscle (from 117 +/- 60 mg in weanling to 417 +/- 112 mg in mature rats), there is no significant change in the total number of arcade arteriole segments per network over this period (from 140 +/- 35 to 181 +/- 51). The mean arcade segment length increased over this period (from 0.96 +/- 0.17 to 1.45 +/- 0.32 mm), but not in proportion to tissue growth. Consequently, the total arcade segment length per unit muscle volume significantly decreased (from 1.36 +/- 0.48 to 0.66 +/- 0.12 mm/mm3). The estimated number of transverse arteriolar trees per muscle (approximately 600) did not appreciably change with growth, leading to a decrease in the number of trees per millimeter arcade arteriole (from 4.4 +/- 1.2 to 2.3 +/- 0.6). Transverse arteriolar trees underwent age-dependent increases in the number of segments within each branch order and in mean segment length. These observations suggest that arteriolar network growth during juvenile maturation occurs by elongation of pre-existing arcade and transverse vessels with angiogenesis occurring in the distal segments of transverse arteriolar trees.

Oxygen and carbon dioxide are known to be heterogeneously distributed in tissues. Extracellular skeletal muscle tissue pH (pHt) also exhibits a spatial variability in vitro, but this has not been examined in vivo. pHt distributions in resting skeletal muscle and the effect of the dispersion of pHt on ischemia and normoxic hypercarbia was therefore studied in an animal model with a multichannel pH microelectrode. Under resting conditions and spontaneous breathing, local pHt (from all animals, n = 10) was found to vary between 6.96 and 7.68 (range), and 70% of the values were within a pH of 7.00-7.32. In each animal the maximum pHt differences (maximum range between the 6 channels of the microelectrode) found were 0.32 +/- 0.11 pH units (mean +/- SD). During tissue acidosis, induced by ischemia, no significant change in the local pHt differences in each animal was seen. During normoxic hypercarbia a 2-fold increase in pHt variability within each animal was noticed (p < 0.01), which suggests that carbon dioxide and buffering effects of the blood are significant factors for the pHt distribution. The pHt distribution range found is of similar magnitude as previously described in in vitro studies on skeletal muscle. Locally varying pHt levels may be of importance as they will affect cellular H+ extrusion, membrane potential and volume control of different cell populations differently.

Flow behavior of erythrocytes in microvessels and glass capillaries with an inner diameter of 10-50 microns was compared in relation to erythrocyte deformation and erythrocyte aggregation. This study was focused on the formation of a marginal cell-free layer, and the thickness was determined using an image processor. Human erythrocytes were perfused through a part of microvascular networks isolated from rabbit mesentery and through glass capillaries. Erythrocyte deformability was modified by treating erythrocytes with diamide, diazene-dicarboxylic acid bis[N,N-dimethylamide], and erythrocyte aggregation was accelerated by adding dextran (with a molecular weight of 70,400) to the perfusion medium. The thickness of the cell-free layer increased with an increase of the inner diameter of flow channel, with lowering the hematocrit, and with increasing the flow velocity of erythrocytes, in both microvessels and glass capillaries. Furthermore, the thickness of cell-free layer decreased with decreasing erythrocyte deformability, while it increased with accelerating erythrocyte aggregation. However, the alteration of the cell-free layer in response to the changes of these hemorheological conditions was more sensitive in microvessels than in glass capillaries. The present study concludes that flow behavior of erythrocytes in microvessels is qualitatively similar to, but quantitatively different from those in glass capillaries, as far as evaluated by the change of the thickness of the marginal cell-free layer.

Using direct visualization techniques, we recently confirmed earlier histologic studies that leukocytes accumulate primarily in the coronary capillaries of ischemic hearts during early reperfusion. The purpose of this study was to determine if pentoxifylline (PTX) would reduce leukocyte trapping in postischemic hearts. Isolated rat hearts were subjected to 30 min of 37 degrees C, no-flow ischemia. Hearts were initially reperfused with diluted whole blood containing fluorescent leukocytes. At 5, (R5), 20, and 35 min of reperfusion, the deposition of leukocytes in the coronary capillaries and venules was observed directly using intravital fluorescence microscopy. Three groups were studied: a non-ischemic control group (group I) and postischemic groups reperfused with diluted whole blood treated with vehicle group II or PTX (5 mM; group III). Postischemic reperfusion with unactivated blood caused a significant trapping of leukocytes in coronary capillaries throughout reperfusion (R5, group I = 2.0 +/- 0.3 vs. group II = 5.7 +/- 0.6 leukocytes/capillary field, p < 0.05). The addition of PTX reduced capillary leukocyte trapping below control values throughout reperfusion (R5, group III = 1.6 +/- 0.2 leukocytes/capillary field, p < 0.05). At R5, there was no statistically significant difference in leukocyte accumulation in venules for all groups (group I = 1.5 +/- 0.6, group II = 3.2 +/- 0.4, group III = 3.3 +/- 0.4 leukocytes/100 microns venule). During the reperfusion period, leukocyte persistence in the capillaries of postischemic hearts (36%) was greater than in the venules (13%). These data indicate that early in reperfusion after myocardial ischemia, leukocyte trapping occurs primarily in the coronary capillaries. PTX reduced early leukocyte trapping in the capillaries. The results also demonstrate that during reperfusion, the mechanisms affecting capillary retention are more persistent than those in the venule. These findings suggest that attempts to attenuate the damaging potential of early leukostasis in capillaries consider the biophysical properties of the leukocyte.

In vivo suppression of neovascularization by in situ administration of human recombinant interferon alpha 2a (hrIFN-alpha 2a) was tested on the chick embryo area vasculosa (AV). Methylcellulose discs, each containing 5 IU of hrIFN-alpha 2a were implanted onto the AV at Hamburger-Hamilton (HH) stage 13, and inhibition of blood vessel growth was morphometrically evaluated between HH stages 20 and 27. Our results show: (i) a decreased extent of the AV; (ii) a decreased AV total vessel length; (iii) modified percent ratios of different classes of AV vessels having a definite length. The observed effects of treating with hrIFN-alpha 2a are likely attributable to inhibition of endothelial cell proliferation.

The assessment of completeness of a sympathectomy can be objectively recorded and documented by dermofluorography. This method enables measurement of increased skin perfusion which leads to an earlier appearance time and steeper initial rise in fluorescence of intravenously administered sodium fluorescein. The most significant parameters are the quotients of the average appearance time and the initial rise in fluorescence of the untreated versus treated leg. Following a successful lumbar sympathectomy, these parameters were outside 3 standard deviations of the values obtained from healthy test persons.

The microcirculation of inflamed human skin was assessed non-invasively using the techniques of laser Doppler flowmetry, hydrogen clearance flowmetry, visible-light spectrophotometry and transcutaneous oximetry. Increases in red cell flux (from a mean of 1.1 in normal skin to 11.5 V in inflamed skin) and haemoglobin saturation (from 49 to 87 and from 38 to 60% with macro- and micro-light-guide spectrophotometry, respectively), contrasted with decreases in transcutaneous pO2 (from 86 to 39 mm Hg). The more intense reactions tended to lead to a lower value of oxygen tension at the surface of the skin than the weaker reactions. A barrier to oxygen diffusion, presented by the infiltrating inflammatory cells, has previously been suggested as the reason for this. The oxygen extraction rate was estimated from spectrophotometry and blood flow measurements, using the Fick principle, and this showed an increase (from 42 to 130 arbitrary units, AU). When the skin was heated to 44 degrees C there was no change seen in this parameter in inflamed skin compared with normal skin (from 114 to 133 and from 14.1 to 14.5 AU), although it tended to increase in the stronger reactions while decreasing in the weaker ones. Extraction measured by a cuff occlusion method (with the same skin temperature) did show an increase however (from 28 to 57 and from 3.2 to 7.2 AU), and this was more pronounced in the stronger reactions. It is suggested that there may be a critical transit time for a red cell, during which it is able to effectively off-load its oxygen. In conditions of very high flow the transit time is reduced and oxygen extraction may be compromised further when diffusion is already limited.