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Biomedical subjects

A R Pries

Publications and source records attributed to A R Pries.

67 records · Page 4Linked to original sources
PubMed1987

A versatile intravital microscope design.

A new intravital microscope system with a versatile arrangement of optical elements and different photosensitive detection devices is described. The image formed by the microscope modified for telescopic imaging is transferred to an optical platform. Through an arrangement of beam splitters and mirrors, the image can be projected simultaneously into three of four different recording systems, including video- and photocameras and a velocity measuring system. In contrast to earlier approaches, the presented system simultaneously generates images on several devices. These images have the same orientation and field of view as that seen through the oculars. This allows the parallel application of different measuring techniques to a given area of the microcirculation.

Humans↗
PubMed1986

Topological structure of rat mesenteric microvessel networks.

Microvascular lengths, diameters, and flow directions were determined in all vessel segments (n = 1303) between bifurcations in three complete rat mesenteric microvessel networks (25 mm2 each) using intravital video- and photomicroscopy. The classification of vessel segments as arteriolar, venular, or av-segments (all segments connecting the arteriolar to the venular tree) was based on purely topological criteria. The topological structure of the networks was analyzed using the Horton-Strahler technique and a new generation scheme. Generation numbers were assigned to the vessel segments on the basis of the number of upstream (in the arteriolar tree) and downstream (in the venular tree) bifurcations. The mean generation number of the av-segments, a characteristic parameter of the generation scheme, reflects the topological structure of the network more accurately than Horton's branching ratio Rb. Both the arteriolar and venular tree of the mesenteric networks were found to be dichotomous branching structures which were neither strictly symmetric nor strictly asymmetric. The topological information obtained was compared to network models generated by different random branching algorithms. The result of this comparison suggests that the network structure changes at a certain generation level. Distal to this generation level, the mesenteric networks resemble a model network generated by random branching at any segment, while the proximal portion is similar to a model allowing random branching at terminal segments only.

Animals↗
PubMed1986

Generalization of the Fahraeus principle for microvessel networks.

Microvessel hematocrits and diameters were determined in each vessel segment between bifurcations of three complete microvascular networks in rat mesentery. Classification of the segments as arteriolar, venular, or arteriovenular (av) was based on flow direction at branch points. Photographic and videomicroscopic mapping was used to obtain quantitative information on the architecture and topology of the networks. This topological information allowed the analysis of hematocrit distribution within a series of consecutive-flow cross sections, each of which carried the total flow through the network. The observed reduction of mean hematocrit in the more peripheral cross sections is explained by the presence of a "vessel" and a "network" Fahraeus effect. The vessel Fahraeus effect results from velocity difference between red cells and blood within the individual vessel segments due to the existing velocity and cell concentration profiles. The network Fahraeus effect is based on the velocity difference of red cells and blood caused by velocity and hematocrit heterogeneity between the vessels constituting any of the complete-flow cross sections. The network Fahraeus effect is found to account for approximately 20% of the total hematocrit reduction and increases toward the most distal cross sections.

Animals↗
PubMed1985

Radial distribution of white cells during blood flow in small tubes.

The radial distribution of white blood cells (WBC) in blood flowing through glass tubes (i.d. 69 micron) was studied as a function of wall shear stress (range 0.1-2.5 Pa) and suspending medium (plasma, buffered saline, high-molecular-weight dextran solution). It was found that, irrespective of the choice of suspending medium, the highest leukocyte flux at high shear stresses was found in the tube center. WBC redistribution was seen upon lowering the shear stresses: A significant shift of WBC flux toward the marginal fluid layers occurred at the expense of the axial region. After replacement of plasma by other media the flow-dependent redistribution of WBCs was qualitatively unaffected. However, suspension of cells in dextran solution (inducing strong red cell aggregation) resulted in enhanced WBC margination, while in saline (no red cell aggregation) axial accumulation was accentuated. The results support the concept of size-dependent radial distribution of particles in flow of mixed suspensions. If applied to the living microcirculation, the data serve to explain WBC margination in microvessels (the first step in the series of events leading to emigration) in terms of a hydrodynamic phenomenon resulting from red cell/white cell interaction. The pronounced flow dependence of WBC margination results primarily from the effect of shear on red cell aggregation which leads to an alteration of the effective particle size distribution in the flowing blood.

Blood↗
PubMed1983

Microphotometric determination of hematocrit in small vessels.

Evaluation and calibration of a microphotometric method for hematocrit determination in microvessels of transilluminated tissues is described. This method is based on the relation of the optical density (OD) of a microvessel to its hematocrit (Hct). The following requirements of the microphotometric system appear essential: narrow-band monochromatic light source with efficient false light suppression, high numerical aperture of the objective and low numerical aperture of the condensor. We used a video system to measure the intensities of incident (Io) and transmitted (I) light. For converting of Io and I into OD values, correcting procedures were evaluated to eliminate the influence of glare, shading, and fading. The calibration procedure was performed with glass tubes of inner diameter (ID) between 13 and 68 microns perfused with red cell suspensions. A function was fitted to the data, correlating OD to ID and Hct. The standard deviation of the original data from this function is +/- 0.02 units of fractional hematocrit. The presented method allows the continuous determination of the hematocrit in a microvessel as well as the off-line evaluation of the hematocrit distribution within a microvessel network.

Animals↗
PubMed1982

Analysis of the hematocrit distribution in the mesenteric microcirculation.

The hematocrit in the microcirculation of the rat's mesentery was determined either by using measurements of optical density (in 56 arterioles and 52 venules) or by counting the number of red cells per unit vessel length (in 63 capillaries) from photographs. The systemic hematocrit (Hsys) averaged 0.42 +/- 0.025. The mean microvessel hematocrit (Hmicro) decreased and its standard deviation increased with decreasing vessel diameter; in capillaries, Hmicro/Hsys ranged between almost zero and 0.86 with an average of 0.36 +/- 0.23. In order to correct Hmicro for the Fahraeus effect, additional experiments were carried out in vitro, in which the tube hematocrit was obtained by centrifugation of glass tubes (I.D. 13-95 micron) perfused with rat's blood of different feed hematocrit. Even after correction for the Fahraeus effect the in vivo data seem to suggest a 'loss of red cells' in the microcirculation. To reconcile the observed hematocrit distribution with the law of mass conservation, model calculations were performed, in which the presence of shunt vessels was assumed on the one hand, and a proportionality between single vessel hematocrit and flow rate on the other. The experimental data are best described by a model which combines the flow dependence of hematocrit and a small shunt component. The positive correlation between single vessel flow rate and Hmicro which is contained in this model also explains an increase of average capillary hematocrit resulting from a more homogeneous flow distribution associated with vasodilatation.

Animals↗
PubMedDate not supplied

OPS imaging of human microcirculation: a short technical report.

Despite the pivotal role of microcirculation in numerous diseases, techniques for the direct assessment of human microcirculation are limited. A new approach based on orthogonal polarization spectral (OPS) imaging (Cytoscan microscope) allows noninvasive observation of human microcirculation in all accessible tissue surfaces. Limitations remain: application of pressure with the instrument affects blood flow, lateral movement of tissue precludes continuous investigation of a given microvascular region, and blood flow velocities above 1 mm/s cannot be measured. We addressed these problems by (a) constructing an attachment to the probe, preventing direct contact of the instrument with the observed tissue area and allowing fixation of the tissue, and (b) implementing a double-flash spatial correlation technique extending the measuring range for blood flow velocities up to approximately 40 mm/s. The modified approach was tested in vitro and in vivo. Velocity readings correlated well with velocities of an external standard (r(2) = 0.99, range 1.9-33.8 mm/s). Pulsatile flow patterns synchronous with heart rate with maximal velocities of about 10 mm/s could be detected in arterioles of the human sublingual mucosa. The modified instrument may prove useful to investigate the microcirculation in the context of research, diagnosis and therapy control.

Adult↗
PubMedDate not supplied

Shear stress modulates the expression of thrombospondin-1 and CD36 in endothelial cells in vitro and during shear stress-induced angiogenesis in vivo.

Binding of thrombospondin-1 (TSP-1) to the CD36 receptor inhibits angiogenesis and induces apoptosis in endothelial cells (EC). Conversely, matrix-bound TSP-1 supports vessel formation. In this study we analyzed the shear stress-dependent expression of TSP-1 and CD36 in endothelial cells in vitro and in vivo to reveal its putative role in the blood flow-induced remodelling of vascular networks. Shear stress was applied to EC using a cone-and-plate apparatus and gene expression was analyzed by RT-PCR, Northern and Western blot. Angiogenesis in skeletal muscles of prazosin-fed (50 mg/l drinking water; 4 d) mice was assessed by measuring capillary-to-fiber (C/F) ratios. Protein expression in whole muscle homogenates (WMH) or BS-1 lectin-enriched EC fractions (ECF) was analyzed by Western blot. Shear stress downregulated TSP-1 and CD36 expression in vitro in a force- and time-dependent manner sustained for at least 72 h and reversible by restoration of no-flow conditions. In vivo, shear stress-driven increase of C/F in prazosin-fed mice was associated with reduced expression of TSP-1 and CD36 in ECF, while TSP-1 expression in WMH was increased. Down-regulation of endothelial TSP-1/CD36 by shear stress suggests a mechanism for inhibition of apoptosis in perfused vessels and pruning in the absence of flow. The increase of extra-endothelial (e.g. matrix-bound) TSP-1 could support a splitting type of vessel growth.

Adrenergic alpha-Antagonists↗