摘要:

Force‐deformation curves are measured for individual human red blood cells by applying an equal and opposite force at diametrically opposite “points” on the red cell rim. Upon release of a cell, it rapidly recovers its unstressed disklike shape in approximately 0.3 sec. This deformation and subsequent recovery process is analyzed with a constitutive equation which describes the finite deformation at constant area of a two‐dimensional viscoelastic solid. From the analysis and the experimental results, values obtained for the “shear modulus of surface elasticity” and “coefficient of surface viscosity” are on the order of4×10−3 dyn/cmand5×10−4 dyn sec/cm(P cm), respectively.

ISSN:0148-6055    

DOI:10.1122/1.549540

出版商:The Society of Rheology    

年代:1979

数据来源: AIP

摘要:

A method is presented for filtering dilute red blood cell suspensions through polycarbonate filters which avoids buildup of deposits on the pores and allows the determination of relative resistance of flow, with and without cells. In the small size range (pores 2.6–3 μm), the relative resistance falls from a high value at lowΔPsto an asymptotic value that depends on hematocrit at highΔP.Using a model for cell flow in the pores, an estimate for the apparent membrane viscosity is attained which is a function of shear rate. The large pore sieves (4.15–5 μm) displayed little sensitivity of relative resistance to imposedΔP.The possible importance of the results for understanding precapillary sphincter control of red blood cell distribution in capillary beds is discussed.

ISSN:0148-6055    

DOI:10.1122/1.549541

出版商:The Society of Rheology    

年代:1979

数据来源: AIP

摘要:

The effects of erythrocyte rigidity on the steady flow viscosity and the oscillatory flow viscoelasticity are examined over a wide range of shear rates. It is found that by hardening the erythrocytes, both the viscosity and the viscoelasticity are generally increased. In addition, the shear rate dependence of the viscoelasticity undergoes an abrupt change in character at higher shear rates. This effect in the viscoelasticity is identified as dilatancy. The elastic component of the complex modulus of viscoelasticity is a particularly sensitive indicator of the rigidity of the cells. These rigidity effects are identified for normal cells, chemically hardened cells, aged cells, and osmotically modified cells.

ISSN:0148-6055    

DOI:10.1122/1.549506

出版商:The Society of Rheology    

年代:1979

数据来源: AIP

摘要:

Mechanical trauma during hemodialyses and heart‐lung bypass can result in shortened red cell life span. The nature of the membrane defect caused by these subhemolytic stresses is not known. The recent literature on the roles of ATP,Ca++,and membrane proteins in erythrocyte deformability is reviewed. New results by the luciferin‐luciferase assay show ATP levels as a function of subhemolytic shear stress for 2‐min exposure, and how ATP levels of normal cells vary when incubated in adenosine or 2‐deoxyglucose. The decrease in cell deformability accompanying mechanical trauma was measured by the increased pressure drop required for the cells to traverse the 3‐μm pores of a Nuclepore filter at a constant volumetric flow rate. Finally, a possible explanation for the observed partial recovery of deformability following adenosine incubation is presented.

ISSN:0148-6055    

DOI:10.1122/1.549507

出版商:The Society of Rheology    

年代:1979

数据来源: AIP

摘要:

Anin vitroperfusion system was used to investigate platelet interaction with subendothelium from rabbit aorta exposed to blood under controlled flow conditions. A morphological technique was used to measure platelet adhesion and thrombus formation. Classical mass transport theory modified to account for the dependence of platelet diffusivity on wall shear rate was used to analyze the results. Platelet adhesion increased with wall shear rate(10–650 sec−1),red cell concentration (10–70%), and platelet concentration(50–300 nl−1)and decreased with axial distance (0–20 mm) from the leading edge. Under these flow conditions platelet adhesion rate was determined predominantly by diffusional transport of platelets to the vessel surface. As shear rate increased to10,000 sec−1,a transition from diffusion to a more kinetic rate limiting adhesion was observed. Few thrombi were observed at low values of platelet concentration (<150/ml), red cell concentration (<25%), or wall shear rate(<200 sec−1).The formation of thrombi increased continuously with increasing wall shear rate to10,000 sec−1even in the region where values of platelet adhesion became relatively independent of shear rate. Thrombus formation was enhanced by an increase in red cell or platelet concentration and was significantly greater on the upstream portions of vessel segments.

ISSN:0148-6055    

DOI:10.1122/1.549542

出版商:The Society of Rheology    

年代:1979

数据来源: AIP

摘要:

Quantitative comparisons are made between calculations based on the best currently available predictive theories and experiments on the motions of rigid biomacromolecules and complexes through fluid media. Hydrodynamic properties calculated are translational diffusion coefficient, sedimentation coefficient, intrinsic viscosity, and rotational relaxation time. Structures for which calculations have been done are those representative of urease, polystyrene latex spheres with adsorbed γ‐globulin, aspartate transcarbamylase, and once‐broken rods. Conclusions are that sensitivity to structure in the hydrodynamic properties has the following order: first normal stress coefficient,Ψ1>rotationalrelaxation time,τ≫intrinsicviscosity,[η]>translationaldiffusion coefficient,DT∼sedimentationcoefficient,S20.w0;and that a model proposed by Abdel‐Khalik and Bird has good predictive capability except for structures which must be modelled by large numbers of subunits.

ISSN:0148-6055    

DOI:10.1122/1.549508

出版商:The Society of Rheology    

年代:1979

数据来源: AIP

摘要:

A Weissenberg rheogoniometer in the oscillatory mode was employed to determine the effect of fibrinolysis and fibrinogen degradation products (FDP) on the development of the dynamic shear moduli in coagulating platelet‐free plasma (PFP) and platelet‐rich plasma (PRP). While the FDP produced by incubation of PFP for 3 min with streptokinase (SK) increased the maximum  shear storage modulus(Gmax′)of PFP, these early FDP decreased theGmax′of PRP clots significantly. The FDP produced at longer incubation periods reduced theGmax′of PRP clots also. The decreasedGmax′in PRP containing FDP appears due to FDP inhibiting the binding of polymerizing fibrin to the platelet membrane. While 10 μ/ml of SK did not produce FDP or induce significant fibrinolysis, clot lysis was complete and rapid in the presence of 20 μ/ml SK. Experiments with crosslinking inhibitors indicate that poorly crosslinked clots are more susceptible to fibrinolysis. In addition, a model for coagulation is presented which accurately fits the entire storage modulus‐versus‐time curve for PFP.

ISSN:0148-6055    

DOI:10.1122/1.549546

出版商:The Society of Rheology    

年代:1979

数据来源: AIP