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H H Lipowsky

Publications and source records attributed to H H Lipowsky.

45 records · Page 3Linked to original sources
PubMed1977

Quantitative studies of microcirculatory structure and function. III. Microvascular hemodynamics of cat mesentery and rabbit omentum.

We made simultaneous measurements of intravascular pressure and red blood cell velocity for vessels which make up the modular configuration of microvascular networks in mesentery and omentum. An analysis of these variables and the computed volumetric flow rates is presented for arterioles which had a maximum diameter of 56 micrometer through the "true capillaries" (typically 7 micrometer for mesentery and 8 micrometer for omentum) to 56-micrometer venules. The spatial variance of pressure and flow is related to topographical features of each network. Vascularization statistics for each network are presented and demonstrate a unique ratio of potential microvascular exchange area to module planar area, with values of 0.71 +/- 0.22 (SD) for omentum and 0.19 "/- 0.03 (SD) for mesentery. Analysis of the volumetric flow rate for each module demonstrates a linear relationship to the planar area of tissue serviced by each modular network. In situ perfusion rates of 1180 ml/min per 100 g and 105 ml/min per 100 g were determined for omentum and mesentery, respectively. The hemodynamic resistance of the omental and mesenteric circuitry was evaluated, and in the case of the omentum, found to be inversely proportional to the planar area of the module. The arterial to venous distribution of pressure and flow for the mosaic of contiguous modules in omentum and mesentery is described and related to the deployment of parallel and serial microvessels of each network.

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PubMedDate not supplied

Testicular hemodynamic changes after the surgical creation of a varicocele in the rat. Intravital microscopic observations.

The present study investigated the effect of a surgically induced varicocele on the dynamics of testicular blood flow. The surface vasculature of the normal and the varicocele-affected testis was examined utilizing intravital epi-illumination microscopy. Application of this technique to the study of the varicocele is new. Blood flow characteristics in surface veins were studied as the surface temperature of the testis was varied. Periodic, reproducible stoppages in blood flow, determined by direct observation of the red blood cells, were seen in seven of eight sham animals at the lower temperatures. These stoppages were abolished and blood flow increased at higher temperatures; stoppages reappeared at lower temperatures. The periodic stoppages were present in only one of eight rats with a proven varicocele (P less than 0.025) at any temperature studied. This loss of blood flow regulation may be the result of a loss of testicular arteriolar tone and may explain the increase in testicular blood flow and temperature elevation observed in association with a varicocele. These findings may provide new insights into the pathophysiology of the varicocele and highlight the need to study the microvascular sequelae of this vascular abnormality.

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PubMedDate not supplied

Image enhancement of the in vivo leukocyte-endothelium contact zone using optical sectioning microscopy.

A major determinant of the strength of leukocyte [white blood cell (WBC)] to endothelium [endothelial cell (EC)] adhesion is the contact area formed between the two cells, which is often obscured by out-of-focus information inherent to intravital microscopy. To improve visualization of the WBC-EC contact zone, techniques of optical sectioning microscopy were developed to enhance brightfield images of WBC-EC adhesion in postcapillary venules of the mesentery of the rat. A 50x/1.0 NA objective was held in a piezoelectric mount that was computer-driven, and video images were obtained by digitizing images from a CCD camera while focusing through the vertical direction in 1 micron steps over a depth of 16 microns. Using measurements of the microscope's optical transfer function, deconvolution of the central image was performed in the Fourier domain using the technique of singular value decomposition with Tikhonov-Miller regulation to remove out-of-focus information. Measurement of the length of the WBC-EC contact zone (LC) in the original images yielded values on the order of 4.32 +/- 1.08 microns (mean +/- SD). The enhanced images showed a significantly 35% smaller LC equal to 2.78 +/- 0.70 micron. Topical application of the chemoattractant f-met-leu-phe resulted in a 26% increase in LC to 3.49 +/- 0.72 micron, thus suggesting that upregulation of adhesion molecules on the WBC membrane results in the recruitment of additional membrane area from surface ruffles into the zone of adhesion. Other advantages of the deconvolution were to visualize structural characteristics of the microvascular wall and parenchymal tissue in greater detail. Thus, brightfield optical sectioning microscopy may provide a valuable tool for in vivo studies of the microvasculature, and serves as a useful alternative to fluorescence microscopy without the undesirable effects of exogenous fluorophores and exposure to ultraviolet radiation.

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PubMedDate not supplied

Mechanics of leukocyte deformation and adhesion to endothelium in shear flow.

The mechanics of leukocyte [white blood cell (WBC)] deformation and adhesion to endothelial cells (EC) in shear flow has been investigated. Experimental data on transient WBC-EC adhesion were obtained from in vivo measurements. Microscopic images of WBC-EC contact during incipient WBC rolling revealed that for a given wall shear stress, the contact area increases with time as new bonds are formed at the leading edge, and then decreases with time as the trailing edge of the WBC membrane peels away from the EC. A two-dimensional model (2D) was developed consisting of an elastic ring adhered to a surface under fluid stresses. This ring represents an actin-rich WBC cortical layer and contains an incompressible fluid as the cell interior. All molecular bonds are modeled as elastic springs distributed in the WBC-EC contact region. Variations of the proportionality between wall shear stress (tau(w)) in the vicinity of the WBC and the resulting drag force (F(s)), i.e., F(s)/tau(w), reveal its decrease with WBC deformation and increasing vessel channel height (2D). The computations also find that the peeling zone between adherent WBC and EC may account for less than 5% of the total contact interface. Computational studies describe the WBC-EC adhesion and the extent of WBC deformation during the adhesive process.

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