ISSN:0167-6865    

DOI:10.1159/000179018

出版商:S. Karger AG    

年代:1995

数据来源: Karger

ISSN:0167-6865    

DOI:10.1159/000179019

出版商:S. Karger AG    

年代:1995

数据来源: Karger

ISSN:0167-6865    

DOI:10.1159/000179020

出版商:S. Karger AG    

年代:1995

数据来源: Karger

摘要:

Capillary density has historically been an important issue, beginning with the discovery of the circulation and extending to the present day. Determination of capillary density provided key evidence supporting the concept that the entire cardiac output passed through microscopic channels in the tissue and returned to the heart. Subsequently, control of capillary density by contractility of the capillaries themselves was proposed by Krogh. Later investigators disputed the notion of capillary contractility and proposed that changes in capillary density were secondary to changes in arteriolar tone or to passive mechanical factors. While this is still the prevailing view, the concept that the capillaries are not totally passive and may, through shape changes of the endothelia, alter the distribution of flow through the capillary network is under active consideration. While views of underlying mechanism vary, there is agreement that capillary density and its control are of fundamental importance to our understanding of the function of the microcirculation.

ISSN:0167-6865    

DOI:10.1159/000179021

出版商:S. Karger AG    

年代:1995

数据来源: Karger

摘要:

This paper examines the authors’ research on capillary network morphology and the heterogeneity of capillary red cell (RBC) perfusion in skeletal muscle with the aim of demonstrating that capillary network structure plays a major role in determining flow distribution. Capillary network morphology was examined by quantifying the heterogeneity of capillary diameters, path and segment lengths, as well as the changes in configuration that occur as vessels accommodate themselves to continual changes of fiber length. Because of the network complexity and the two-phase nature of the perfusing blood, both spatial (i.e. among capillaries) and temporal heterogeneity of capillary perfusion were predicted to result. By means of computer analysis of video images of the microcirculation in vivo, we have demonstrated that more than 70% of the total spatial heterogeneity of capillary RBC perfusion arises from the capillary network as opposed to the arterioles, and that RBC flow continuously redistributes among capillaries. The spatial heterogeneity increases substantially as the arteriolar input to the network falls, and the data predict that during low-flow states, the network will fail to distribute blood properly among its constituent vessels. Thus passive rheological mechanisms and capillary network morphology are important determinants of functional capillary densit

ISSN:0167-6865    

DOI:10.1159/000179022

出版商:S. Karger AG    

年代:1995

数据来源: Karger

摘要:

We briefly summarize our findings on alterations in capillary structure in skeletal muscle and heart in response to up to 30 min of ischemia. In frog sartorius muscle, reactive hyperemia was absent in atrophy. Increased spatial heterogeneity of red cell velocity in individual capillaries was observed, as were increases in the percentage of capillaries with damaged endothelium and white cell volume density in capillaries. Examination of the effect of aging on the response of the vascular bed to 30 min ischemia in extensor digitorum longus muscle of Fisher 344 rats suggested that the lack of postischemic hyperemia and structural alterations in frog muscle were related to disuse rather than aging per se. However, the specific study of disuse in rat extensor digitorum longus muscle after chronic application of tetrodotoxin revealed both capillary damage and a postischemic hyperemic response. It suggested an effect of the degree of tissue deterioration on the hyperemic response after short-term disuse in rat muscle, compared to longer-term atrophy in frog. Morphometric data in isolated rabbit heart suggested a link between microvascular compression as a result of tissue edema and decreased perfusion after 30 min total ischemia.

ISSN:0167-6865    

DOI:10.1159/000179023

出版商:S. Karger AG    

年代:1995

数据来源: Karger

摘要:

Functional capillary density is variable in both normal and diseased tissue. When this parameter is defined as the number of capillaries that possess red blood cell transit, changes in functional capillary density reflect mechanisms that modulate the entrance of red blood cells into the capillaries. These mechanisms have anatomical origin, whereby the capillary diameter changes, and may also be hydrodynamic, when flow conditions prevent red blood cells from entering a capillary branch. An intrinsic feature of both processes is that capillaries undergo lumenal changes. Capillary lumen is determined by a composite of mechanical and cellular factors, where intravascular pressure is one of the principal determinants affecting diameter as a consequence of the elastic properties of the capillary/tissue system. The hydration of the surrounding tissue and the cellular volume regulation of the endothelium are additional factors. There is increasing evidence that capillaries possess contractility and that this phenomenon has spontaneous components. Consequently, functional capillary density is the resultant of both passive and active processes present at the level of individual vessels.

ISSN:0167-6865    

DOI:10.1159/000179024

出版商:S. Karger AG    

年代:1995

数据来源: Karger

摘要:

Functional capillary density (FCD) is one of the parameters obtained by intravital microscopy using epi-illumination of the tissue surface or trans-illumination of thin tissue layers. FCD, defined as the length of red cell-perfused capillaries per observation area (cm-1), has been used as an indicator of the quality of tissue perfusion in various animal models. Quantitative analysis of FCD in randomly selected regions of the tissue is performed by means of a computer-assisted video analysis system which allows calculation of the length of RBC-perfused capillaries. Basically, two different mathematical approaches can be employed: the first approach is based on the addition of the distances between two neighboring points (pixels) on the video screen (Pythagorean principle). The second approach uses the superimposition of a grid system that allows estimation of the capillary length by counting the number of intersections between the capillaries and the grid lines (stereological approach). The immanent error has been calculated in our laboratory to be ± 1 % with the Pythagorean and ± 5% with the stereological method. Beside these systematic errors of computerized measurement, the individual (user-dependent) errors occurring during recognition and redrawing of the capillaries on the video image with use of a digitizing tablet are in the range of ± 10% (intraindividual) and ± 70% (interindividual) for the recognition and ± 3% (interindividual) for the redrawing procedure. Our studies indicate that the errors resulting from the use of a computer-assisted calculation (Pythagorean or stereological approach) or the user-assisted redrawing of the capillaries are negligible when compared to the errors made during recognition of the capillaries on the video screen. The methods are applied for assessment of FCD in two different microcirculation models of skin muscle and pancreas yielding highly reproducible, user-independent results under physiologic conditions and the pathophysiologic conditions of ischemia-reperfu

ISSN:0167-6865    

DOI:10.1159/000179025

出版商:S. Karger AG    

年代:1995

数据来源: Karger

摘要:

The relationship between red blood cell mechanics and functional capillary density is examined. Experimental observations of capillary recruitment in skeletal muscle have shown sequential recruitment and derecruitment of capillaries fed by a single arteriole, implying that flow may cease in individual capillaries at small nonzero driving pressures. Such behavior is not expected in uniform blood-perfused tubes, but could occur when moving red cells encounter geometrical irregularities in capillaries. From known elastic properties of the red cell membrane, a lower bound is computed for the pressure required to sustain red cell motion in irregular capillaries. This may be an underestimate of the pressure required, because it neglects the viscous resistance of the red cell membrane when it undergoes transient deformations. Simulations including membrane viscosity show that viscous effects can substantially increase flow resistance. It is concluded that the mechanical properties of red blood cells can play a significant role in the modulation of functional capillary density.

ISSN:0167-6865    

DOI:10.1159/000179026

出版商:S. Karger AG    

年代:1995

数据来源: Karger

摘要:

During disease, the flow of blood cells through the capillary network is one of the most perilous events in the microcirculation. Capillary distensibility, cytoplasmic activity of endothelial cells, red cells and leukocytes play an important role in capillary perfusion. Occlusion of capillaries is one of the early signs of vascular failure and is encountered in many different conditions and organs. Adhesion of leukocytes to the endothelium via expression of membrane adhesion molecules leads to microvascular entrapment with capillary occlusion.

ISSN:0167-6865    

DOI:10.1159/000179027

出版商:S. Karger AG    

年代:1995

数据来源: Karger