Biomedical subjects

H H Lipowsky

Publications and source records attributed to H H Lipowsky.

At least 19 recordsLinked to original sources

PubMed2004

Inflammation- and ischemia-induced shedding of venular glycocalyx.

Alterations in the composition of the glycocalyx of venular endothelium in postcapillary venules (rat mesentery) were explored in models of inflammation and ischemia-reperfusion injury. Lectins were covalently linked to fluorescently labeled microspheres (0.1-microm diameter) or directly labeled with FITC. Adhesion of lectins specific for glucose and galactose residues of glycosaminoglycans (GAGs) and other components of the endothelial glycocalyx decreased dramatically after superfusion of the mesentery with the chemoattractant N-formylmethionyl-leucyl-phenylalanine and during reperfusion after 60-min ischemia. These reductions were significantly attenuated by superfusion with pertussis toxin (PTX), suggesting that shedding of glycocalyx was mediated by G proteins. Adhesion of microspheres linked with antibody for syndecan-1, a major proteoglycan to which GAGs are bound, revealed increased labeling as GAGs were lost and permitted greater numbers of spheres to adhere to the protein core, which was not shed. Induction of ischemia by occluding proximal microvessels for 60 min resulted in a 40% increase in galactosaminoglycans and a 15% increase in glucosaminoglycans on the endothelium, which was not inhibited by PTX. Reperfusion of vessels led to a rapid loss of GAGs that was inhibited by pretreatment with PTX, with 40% of galactosaminoglycans and 25% of glucosaminoglycans accumulated being removed by G protein-mediated shedding and the remainder freely convected away by fluid shear. We conclude that the composition of the glycocalyx results from a balance of the rate of biosynthesis of GAGs by the endothelial cell and their shedding, which may be mediated by intracellular and/or membrane-bound proteases or lyases released or activated by G protein signaling.

Animals↗

PubMed2002

Role of glycocalyx in leukocyte-endothelial cell adhesion.

The binding of fluorescently labeled microspheres (FLMs, 0.1-microm diameter) coated with antibody (1a29) to ICAM-1 was studied in postcapillary venules during topical application of the chemoattractant N-formylmethionyl-leucyl-phenylalanine (fMLP). FLM adhesion to endothelial cells (ECs) increased dramatically from 50 to 150 spheres per 100-microm length of venule after superfusion of the mesentery with fMLP and equaled or exceeded levels of leukocyte (WBC) adhesion. Removal of the EC glycocalyx by micropipette infusion of the venule with heparinase increased FLM-EC adhesion to levels attained with fMLP. Subsequent application of fMLP did not increase FLM adhesion further, suggesting that the FLMs saturated all ICAM-1 binding sites. Perfusion with heparinase after suffusion with fMLP significantly increased FLM-EC adhesion above levels attained with fMLP. However, WBC adhesion fell because of possible removal of selectins necessary to maintain WBC rolling at the wall. It is concluded that the glycocalyx serves as a barrier to adhesion and that its shedding during natural activation of ECs may be an essential part of the inflammatory response.

Animals↗

PubMed2001

Leukocyte rolling in rat mesentery venules: distribution of adhesion bonds and the effects of cytoactive agents.

A new method of analyzing in vivo measurements of leukocyte WBC rolling along venular endothelium (EC) has been developed to extract insightful information on the dynamics of WBC-EC bond formation and disruption. The rolling velocity of WBCs was obtained by intravital microscopy of rat mesenteric venules. For the "spontaneous" rolling observed following exteriorization of the mesentery, we estimated that the average distance between clusters of adhesion bonds which tether a rolling cell to the venular wall was about 2 microm, and that the average lifetime of a bond cluster at the trailing edge of the rolling cell, from its exposure to the tensile force to its release, was on the order of 0.05 s. Both the inter-cluster distance and the lifetime were significantly reduced by treatments with the chemoattractant N-formyl-methionyl-leucyl-phenylalanine and the cytokine interleukin-1, while the average lifetime of the stretched bond clusters was not significantly changed by treatment with the cytoskeleton-modifying agents cytochalasin B and colchicine. Each of the four treatments significantly reduced the heterogeneity in the cell rolling velocity, presumably by the selective recruitment of WBC subsets from the circulating WBC population or by a reduction in the heterogeneity of endothelial adhesiveness. These results were analyzed in the context of in vitro data in the literature on molecular bonds of cell adhesion. The findings suggest that, in the case of "spontaneous" rolling, there are on average approximately 2-3 clusters of adhesion bonds between a rolling cell and the vessel wall, and approximately five bonds in each cluster.

Animals↗

PubMed2000

Influence of erythrocyte aggregation on leukocyte margination in postcapillary venules of rat mesentery.

The role of erythrocyte (red blood cell; RBC) aggregation in affecting leukocyte (white blood cell; WBC) margination in postcapillary venules of the mesentery (rat) was explored by direct intravital microscopy. Optical techniques were refined and applied to relate the light-scattering properties of RBCs to obtain a quantitative index of aggregate size (G), which, under idealized conditions, represents the number of RBCs per aggregate. WBC margination, defined as the radial migration of WBCs to the venular wall and their subsequent rolling along the endothelium, was measured as the percentage of the potentially maximal WBC volumetric flux within the microvessel lumen (F(WBC)(*)). In normal blood, F(WBC)(*) increased exponentially fourfold, and G increased from 1 to 1.15 as wall shear rates () were reduced from a steady-state value of approximately 600 to <100 s(-1) by proximal occlusion with a blunt microprobe. Enhancement of aggregation by infusion (iv) of dextran 500 (428 kDa), to attain a systemic concentration of 3 g/100 ml, resulted in a four- and sevenfold increase in G and F(WBC)(*), respectively, as was reduced below 100 s(-1). Inhibition of RBC aggregation by infusion of dextran 40 (37.5 kDa) caused F(WBC)(*) to fall to one-half of its steady-state level for < 100 s(-1). Thus it appears that the well-known increase of WBC margination with reductions in is strongly dependent on the occurrence of RBC aggregation. Increasing the extent of RBC aggregation during reductions in also increased the firm adhesion of WBCs to the endothelium because of an enhanced probability of contact between leukocytes and the postcapillary venular wall.

Animals↗

PubMed1999

Capillary recruitment in response to tissue hypoxia and its dependence on red blood cell deformability.

The effect of reduced red blood cell (RBC) deformability on microvessel recruitment attendant to a reduction in tissue PO2 was studied in rat cremaster muscle using indicator-dilution techniques. Transit times (TT) of fluorescently labeled RBCs (TTRBC) and plasma (TTPl) between functionally paired arterioles and venules were obtained from their dispersion throughout the microvascular network. Changes in PO2 were effected by superfusing the tissue with Ringer solution deoxygenated to different levels. Arteriolar blood flow (Q) was measured with the two-slit technique, and the vascular volume (V) occupied by RBCs and plasma was computed from the product of Q x TT during bolus infusions of rat and less deformable human RBCs to obtain VRBC and fluorescently labeled albumin to obtain VPl. Measurements of TTRBC and TTPl permitted computation of an average flow-weighted tissue (microvascular) hematocrit (HM) relative to systemic values (HS). During infusions of autologous rat RBCs, Q and total V increased threefold in response to hypoxia, whereas normalized RBC TT (TTRBC/TTPl) and normalized tissue hematocrit (HM/HS) did not show a significant trend, indicating an increase in the number of pathways through which the RBCs can traverse the network because of spatial recruitment of capillaries. In contrast, during infusions of human RBCs, TTRBC/TTPl and HM/HS decreased significantly in response to hypoxia. Although Q exhibited an increase similar to that during rat RBC infusions, VRBC exhibited a smaller increase compared with VPl, suggesting that reduced RBC deformability leads to a redistribution of RBCs through larger-diameter pathways within the network and exclusion of these RBCs from pathways normally recruited during hypoxia. Hence, reduced RBC deformability may adversely affect capillary recruitment and physiological mechanisms that ensure adequate delivery of oxygen to tissue.

Animals↗

PubMed1997

Shear rate dependency of red cell sequestration in skin capillaries in sickle cell disease and its variation with vasoocclusive crisis.

OBJECTIVE: To develop techniques for assessing the sequestration of red blood cells (RBCs) in skin capillaries of sickle cell disease (SCD) patients due to RBC adhesion to endothelium (EC) and RBC aggregation, and to determine the extent to which these processes correlate with onset of painful vasoocclusive crisis. METHODS: Video recordings of nailfold capillaries in the skin of patients with SCD were made during steady-state periods and episodes of painful crisis. A transient low-flow state was induced with a pressure cuff and reductions in RBC velocity were measured by spatial cross-correlation of light intensity along arterial and venous capillary limbs. An RBC accumulation index (AI) was calculated from RBC flow to represent the percentage of arterial in-flow sequestered in a capillary. An index of hematocrit (HI) was derived from axial distributions of light intensity, and a sequestration index (SI) was calculated to represent the relative increase of venous limb HI relative to that in the arterial limb with onset of stasis. RESULTS: Both AI and SI increased dramatically from zero at steady flow to a maximum as shear rates within the capillary were reduced to zero. The increase was small until shear rates (gamma) fell below a transition value (gamma T), following which both AI and SI increased sharply with onset of stasis. For 20 < or = gamma < gamma T the transient increase in AI was significantly elevated in the order AICRISIS > AISTEADY STATE > AICONTROL, thus reflecting increasing RBC sequestration in the venous limb due to either adhesion or aggregation. Compaction of RBCs in the venous limb was evidenced by increased SI that was greater than control for both steady-state and crisis subjects, but insignificantly elevated during crisis compared to steady state, thus supporting a lesser role of RBC aggregation. CONCLUSIONS: Transient sequestration of sickle RBCs in the low-flow state appears to be dominated by RBC-EC adhesion, which becomes enhanced during crisis. Although aggregation may enhance adhesive contact of RBCs with EC, it does not increase to the same extent as the rate of sequestration, thus reflecting a greater role of RBC-EC adhesion.

Anemia, Sickle Cell↗

PubMed1996

Effects of leukocyte-capillary plugging on the resistance to flow in the microvasculature of cremaster muscle for normal and activated leukocytes.

The effects of leukocyte (WBC) sequestration in the capillary network on resistance to flow (RA-V) were obtained during bolus infusions of WBCs in cremaster muscle (hamster). RA-V was calculated from simultaneous measurements of arteriole to venule pressure drop and arteriolar red cell velocity. Bolus infusions of red cells (RBCs) alone resulted in a 5% decrease in RA-V, due to the clearance of circulating WBCs from the network. Infusions of RBCs with leukocrits of one to nine times systemic resulted in insignificant transient increase in RA-V of 5 to 10%. The effect of WBC activation was studied by their incubation in N-formyl-methionyl-leucyl-phenylalanine (FMLP) to activate (and stiffen) the polymorphonuclear WBCs (PMNs) or phorbal myristate acetate (PMA) to activate all WBCs in the bolus. Compared with normal WBCs, infusions of mixtures of RBCs and activated WBCs had no significant effect on the transient increase in resistance as the bolus traversed the capillary network. However, mixtures with either normal or FMLP-treated WBCs increased the steady state RA-V in proportion to the cumulative number of WBCs infused, due to residual capillary plugging following washout of the bolus. The cumulative infusion of 20 x 10(6) normal or FMLP-activated WBCs resulted in a 25% increase in RA-V above baseline. With PMA activation, cumulative infusions of only 5 x 10(6) WBCs in the RBC suspension also resulted in a 25% increase in RA-V, which was three times the increase obtained for an equal number of FMLP-activated WBCs. Following the cumulative infusion of 12 x 10(6) PMA-activated WBCs, RA-V increased inordinately to approximately 250% of baseline. These substantially greater increase in capillary plugging and RA-V with PMA activation were in accord with the threefold greater number of stiffened lymphocytes (which do not respond to FMLP) relative to PMNs in the boli. Thus, capillary plugging by activated WBCs may have a far greater detrimental effect on blood flow through the microvasculature compared to normal WBCs, and the extent of this effect is strongly dependent on the number of activated WBCs in the circulation.

Animals↗

PubMed1996

Leukocyte rolling velocity and its relation to leukocyte-endothelium adhesion and cell deformability.

To explore the relationship between the rolling velocity of leukocytes (VWBC) and wall shear rates (gamma), measurements of VWBC were made along the length of rat mesenteric venules in which a gradient in gamma was induced by compressing the venule with a blunted microprobe to form a stenosis in which gamma varied from 300 to 1500 s-1. For individual WBCs that rolled through stenosis, VWBC was proportional to gamma for its entire range, in contrast to previous studies that have shown a plateau in VWBC vs. gamma for the ensemble population. Comparisons of the slope of VWBC/gamma for individual cells with ensemble values of VWBC obtained in the entrance region of the stenosis were made during suffusion of the tissue with the chemoattractant N-formylmethionyl-leucyl-phenylalanine (FMLP), to increase WBC-EC adhesion and WBC stiffness, or colchicine and cytochalasin B to increase WNC deformability. Under control conditions, the slope of individual cells was significantly 20% greater than VWBC/gamma, whereas it was significantly reduced by 48% during suffusion with FMLP. With exposure to colchicine, the slope was 78% lower than VWBC/gamma and compared with control was similar in magnitude to that obtained with FMLP. Cytochalasin also reduced the slope by 22% compared with control and 34% compared with VWBC/ gamma. The diminished slopes of VWBC vs. gamma were consistent with published theoretical models that suggest a reduced slope with increased strength of adhesion of WBC deformability. It is thus concluded that the apparent plateau in VWBC vs. gamma arises due to the heterogeneity of adhesive and/or deformability properties in the ensemble population of circulating WBCs.

Animals↗

PubMed1994

Leukocyte sequestration in the microvasculature in normal and low flow states.

Techniques of indicator dilution were applied to determine the relative transit times (TTs) of fluorescently labeled leukocytes (TTWBC), red blood cells (TTRBC), and plasma (TTpl) between functionally paired arterioles and venules in hamster cremaster muscle in normal and low flow states. In the normal flow state, paired measurements of TTWBC/TTpl in arteriovenous (A-V) pairs bounding the true capillaries averaged 0.75 +/- 0.08 (SE) s and were not significantly different from an average TTRBC/TTpl of 0.78 +/- 0.06 (SE) s as WBCs appeared to traverse the capillary segment through more centralized preferential pathways. In larger-diameter A-V pairs, significantly larger (10%) values of TTWBC/TTpl were found compared with TTRBC/TTpl due to margination of WBCs in postcapillary venules. To assess the relative effects of WBC-capillary plugging and WBC adhesion in venules on flow resistance, TTWBC was measured in normal and low flow states, with the latter induced by systemic administration of sodium nitroprusside, which resulted in an increase in TTpl from a norm of 1.08 +/- 0.16 to 2.62 +/- 0.44 (SE) s (P < 0.05). With onset of the low flow state, TTWBC/TTpl, the number of plugged capillaries, and the duration of capillary plugs did not change significantly from the norm. In contrast, the rate at which WBC-endothelium (-EC) adhesion increased with successive bolus injections increased approximately eight-fold during hypoperfusion. Estimates of the percentage increase in segmental resistance at the capillary level (due to plugging) and in postcapillary venules (due to EC adhesion) revealed that venous resistance may increase at a threefold greater rate due to WBC sequestration with each successive bolus infusion. Inasmuch as hemodynamic resistance in capillary and venular segments is of the same order of magnitude in the normal flow state, it appears that WBC adhesion in venules may have a far greater deleterious effect on microvascular blood flow in the low flow state.

Animals↗

PubMed1994

The mean filtration pressure of leukocyte suspensions and its relation to the passage of leukocytes through nuclepore filters and capillary networks.

OBJECTIVE: To quantitatively evaluate the deformability of bulk suspensions of leukocytes (WBCs), account for the variance of individual cell mechanical properties, and deduce the potential for WBC entrapment within the capillary network in response to alterations in cell properties. METHODS: The transient washout of WBCs initially trapped under low perfusion pressure in 5-microns pores of Nuclepore filters was analyzed for a 0.2-ml bolus of WBCs (derived from hamsters) with equal numbers of filter pores and cells, to characterize the statistical distribution of pressures, Pyield, required to dislodge the cells. Contributions of the variance in WBC diameter, pore diameter, and cremaster muscle capillary diameter to Pyield were estimated with a WBC cortical shell model and an analysis of the probability function of the ratio of WBC to pore diameter, lambda. RESULTS: For normal WBCs, Pyield exhibited a log-normal distribution with mean (Pyield) of 0.59 cmH2O. Incubation of cells in cytochalasin-B reduced (Pyield) almost 50%, whereas phorbol myristate acetate increased (Pyield) twofold. Incubation in N-formyl-methiolnyl-leucyl-phenylalanine had no significant effect on (Pyield), as polymorphonuclear cells became permanently trapped in the filter. The fluorescent dyes acridine orange, acridine red, and tetramethylrhodamine isothiocyanate increased (Pyield) as much as 10-fold, whereas steady-flow filtration methods showed no alteration. Analysis of the distribution of lambda revealed that due to their smaller pore diameters, in vitro filtration methods may overestimate in vivo values of (Pyield) by almost twofold. CONCLUSIONS: The transient filtration of WBC suspensions appears to be much more sensitive to subtle alterations in WBC deformability than steady-flow methods and may provide greater insight into the determinants of capillary perfusion. Estimates of (Pyield) are comparable to those obtained with micropipettes and permit analysis of substantially greater numbers of cells within a sample. Fluorescence labeling techniques should be used with caution, as they may dramatically alter cell properties to an extent undetectable by direct in vivo observations.

Animals↗

PubMed1993

Effect of erythrocyte deformability on in vivo red cell transit time and hematocrit and their correlation with in vitro filterability.

Indicator dilution techniques were applied to measure mean transit time of fluorescently labeled red blood cells (RBCs) (TTRBC) and plasma (TTpl) between functionally paired arterioles and venules (A-V) in cremaster muscle (rat) for normal RBCs and cells hardened by in vitro incubation in graded concentrations of glutaraldehyde. Dispersion of a bolus introduced into the contralateral femoral artery permitted computation of TT by cross-correlation of fluorescence intensity-time curves in A-V pairs. Parallel in vitro assessments of RBC deformability were made by filtration through 5-microns pore Nuclepore filters to express deformability in terms of the ratio of resistance to flow through a pore with RBCs present to that with suspending medium alone, beta. The average microvascular hematocrit (Hmicro) normalized with respect to systemic hematocrit (Hsys) was calculated from TTRBC and TTpl. For 26 A-V pairs of the third and fourth orders of branching, TTRBC averaged 0.63 sec for normal control cells (beta = 2.61), and TTpl averaged 0.85 sec with an average TTRBC/TTpl equal to 0.85. The corresponding value of Hmicro/Hsys was significantly < 1 and averaged 0.87. This greater value of Hmicro/Hsys compared to direct measurements in the literature was attributed to the unique ability of the indicator dilution technique to account for red cell flux throughout the network. For hardened RBCs with beta < 10, TTRBC/TTpl and Hmicro/Hsys increased on average 30%, but were weakly correlated with increasing beta due to redistribution of RBCs throughout pathways of lesser resistance. However, as beta rose from 10 to 20, these pathways became overwhelmed by hardened RBCs and TTRBC/TTpl increased threefold due to retardation of the RBC flux, with a concomitant rise in Hmicro/Hsys. These results clearly demonstrate the extent to which diminished RBC deformability of a magnitude found in clinical disorders may affect microvascular perfusion.

Animals↗

PubMed1991

Dynamics of leukocyte-endothelium interactions in the splanchnic microcirculation.

In vivo dynamics of the interaction between leukocytes and the endothelium following direct activation of the white blood cells (WBCs), apart from possible endothelial cell activation, were studied in arterioles, capillaries, and venules of splanchnic tissue (rabbit omentum). WBCs were isolated using either density gradient or centrifugation techniques, labeled with fluorescent dyes, and exposed to physiological solutions with or without the chemoactivator N-formyl-methionyl-leucyl-phenlyalanine (FMLP). WBCs isolated using standard density gradient separation techniques rapidly disappeared from the circulating pool following a bolus injection and were sequestered in lung microvessels. The centrifugation technique produced cells that circulated for at least 60 min. WBCs directly activated with FMLP adhered to venular endothelium but not to arteriolar endothelium, suggesting that differences in hydrodynamics in the arteriolar and venular network or fundamental differences between arteriolar and venular endothelia may explain the lack of leukocyte-endothelium adhesion (LEA) in arterioles. WBCs pretreated with FMLP had significantly longer attachment times than nontreated cells, 13.4 and 2.5 sec respectively, which may be indicative of specific receptor chemistry. Similarities in the LEA attachment-detachment process for splanchnic tissue with that previously reported for lymphoid tissue suggest that a fundamental process of cell to cell interaction may exist in all tissues.

Animals↗

PubMed1991

In vivo mechanical properties of leukocytes during adhesion to venular endothelium.

Transient deformations of leukocytes (WBCs) were studied during their saltation along post-capillary venous endothelium (EC) in mesentery of the rat. During intermittent adhesion of WBCs to EC, prevailing fluid shear stresses, tau wall, resulted in a stepwise loading of the WBC upon attachment with a transient increase in length, L(t), and reduction in height, H(t). Measurements of L(t) and H(t) from frame-by-frame analysis of video recordings were modelled as the simple shear of a standard linear viscoelastic solid to facilitate calculation of the elastic (k1, k2) and viscous (mu) elements with k1 in parallel with serial elements k2 and mu. The magnitude of tau wall was determined from measurements of red cell velocity within the venule. During the spontaneous adhesion of WBCs, a value of cell viscosity (mu) of 45 Poise was determined. Stimulating adhesion by topical application of the chemoattractant FMLP resulted in a 15-fold increase of mu to 668 Poise. Transient deformations during topical application of cytochalesin B to disrupt actin fibers within the WBC, yielded a 40% reduction in k1, compared to an 80% reduction with colchicine which disrupts the microtubule structure. Thus, colchicine treated cells appear to be twice as deformable as cells treated with cytochalesin. During adhesion stimulated by the cytokine Interleukin-1, mu increased 50% without changes in k1 and k2, possibly due to slight activation of the WBC.

Animals↗

PubMed1989

Quantitative assessment of microcirculation in the rat dental pulp in response to alpha- and beta-adrenergic agonists.

Responses to intra-arterial injections of the alpha-agonist, norepinephrine, the beta-agonist, isoproterenol, and to selected blockers were investigated in vivo by intravital microscopy. Luminal diameters (D) of pulpal microvessels and red cell velocities (Vrbc) were measured simultaneously to facilitate calculation of volumetric blood flow (Q). Norepinephrine caused a decrease in D, mean red cell velocity (Vm) and Q within individual microvessels. These responses were blocked by the alpha-antagonist, phenoxybenzamine. In response to the arteriolar D increase and venular D and Q decrease with isoproterenol, a transient increase in arteriolar Q was followed by a decrease within the first 60 s. No such effects were observed when the beta-antagonist, propranolol, was administered before the isoproterenol injection. The biphasic response in Q in response to isoproterenol is most likely related to the low compliance of the pulp. In the low-compliance environment a passive compression of venules could result from an active dilation of arterioles with an attendant rise in extravascular tissue pressure.

Animals↗

PubMed1989

In vivo and in vitro measurements of red cell velocity under epifluorescence microscopy.

Studies of blood flow in mesentery, cremaster muscle, and small bore glass tubes were performed to obtain a relationship between mean velocity (Vmean) and red cell velocity using the two-slit method under epifluorescence (Vepi) and transillumination (Vtrans) microscopy. The velocities Vepi and Vtrans obtained in vivo for 47 measurements in arterioles and venules (12- to 51-micron internal diameter) were linearly related by Vepi = 0.83 Vtrans + 0.074, and the ratio Vepi/Vtrans decreased gradually with increasing vessel diameter (P less than or equal to 0.05). In vitro studies in tapered glass tubes (diameter 30-70 micron) were conducted for feed hematocrits (HF) from 10 to 40%. Under transillumination, Vtrans/Vmean was nearly constant with an average of 1.56 +/- 0.16 (SD) for all hematocrits and diameters. The velocity ratio, Vepi/Vmean, however, decreased with HF from 1.8 to 0.8 as HF was increased from 10 to 40%. Theoretical considerations suggest that the variations of Vepi/Vmean with tube hematocrit and diameter might result from attenuation of the excitation light by absorption and scattering by red cells, and also due to a finite depth of field of the microscopic objective.

Animals↗

PubMed1989

Role of leukocyte-endothelium adhesion in affecting recovery from ischemic episodes.

The role of the inflammatory process in the onset of sickle cell crisis has not been fully elucidated, although there is evidence for leukocytosis and enhanced leukocyte to endothelium adhesion. The elevated LEA typical of inflammation may impede recovery from transient ischemic episodes by increasing the resistance to blood flow, which in the case of sickle cell disease may exacerbate the "vicious cycle" of HbS deoxygenation which leads to microvascular stasis. Recent studies on the mechanics of white blood cell margination and adhesion in postcapillary venules of laboratory animals, either in the low-flow state or following tissue exposure to chemoattractants, reveal a marked rise in intravascular resistance with LEA. Such increases may be as great as twofold with as few as 6 WBCs adhering per 100 microns of venule length. In human subjects, leukocytosis attendant to crisis has been correlated with increased time to recover from induced periods of ischemia in skin capillaries. Thus, further definition of the role of the inflammatory process in crisis is needed in light of microvessel obstruction in the low-flow state.

Anemia, Sickle Cell↗

PubMed1989

Leukocyte margination and deformation in mesenteric venules of rat.

White blood cell (WBC) margination and rolling were studied in venules (20-60 microns in diameter) in rat mesentery to examine the relationship between WBC rolling velocity (Vwbc), flux (Fwbc, cells/min), and deformation; and red blood cell (RBC) velocity (Vrbc), wall shear rate (gamma), and microvessel hematocrit (Hmicro). For a range of 1.0 less than or equal to Vrbc less than or equal to 5.0 mm/s, Vwbc remained constant (congruent to 50 microns/s). The volume flux of WBCs rolling along the venular wall (normalized to systemic WBC concentration) decreased nonlinearly from 30 to 5% of total luminal flux as gamma ranged from 50 to 800 s-1 and was more strongly correlated with gamma compared with Fwbc vs. gamma. As indicated by the rolling volumetric flux, margination was weakly affected by Hmicro, except for Hmicro greater than 50% where margination increased. Deformation of WBCs was quantitated during their rolling contact with the endothelium (EC) in terms of their length and height. As gamma increased from 50 to 800 s-1, WBCs elongated to 140% of their estimated undeformed diameter, and the contact area between WBC and EC increased 3.6-fold. These data suggest that with increased gamma rolling of WBCs along the EC decreases, since only the most deformable WBCs of the circulating population persist in maintaining contact with the endothelium. It is concluded that Vwbc is invariant with elevations in gamma, since the greater deformations of rolling WBCs at high shear result in greater adhesive forces attendant to increased WBC-EC contact area, which attenuate increases in Vwbc.

Animals↗

PubMed1988

Leukocyte endothelium adhesion and microvascular hemodynamics.

In the present study we have attempted to provide quantitative details of hemodynamic determinants of leukocyte to endothelium adhesion in the microvasculature. To this end, several hypotheses have been advanced to suggest that the preferential adhesion of leukocytes in the larger venules (30-50 microns diameter) rests upon the inherent ability of the microvasculature to compensate for small perturbations in resistance and that WBC deformability may play a significant role in this process. Flow redistribution and attendant arteriolar vasomotor adjustments may forestall LEA in the larger collecting venules of the network, where venous obstruction may be countered by bringing the full weight of the arteriovenous pressure gradient to oppose WBC adhesion. Direct measurements of the force of adhesion suggest that with diminishing vessel diameter, as for example in the immediate post-capillary venules, WBC dispersal forces will be greatest due to dramatic increases in the proportionality between force and wall shear stress. This event would tend to preclude adhesion in the smallest venular microvessels. It has also been shown that there is a strong potential for WBC deformability to affect the adhesion process by modification of the shear stresses acting on the WBC surface, as evidenced by an inverse relationship between force and wall shear stress and direct observations of WBC shape changes with increasing shear.

Animals↗