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Biomedical subjects

G R Cokelet

Publications and source records attributed to G R Cokelet.

32 records · Page 2Linked to original sources
PubMed1982

Influence of wall surface on the flow of blood through endothelial-lined glass tubes.

It has been proposed that the presence of endothelial cells lining small vessels decreases resistance to microcirculatory blood flow. Results of previous investigations have been inconclusive when fibrin-coated glass tubes were used to approximate the endothelial layer. Estimates of the decrease in apparent viscosity for blood flow in these tubes have ranged from near-zero to 50% when compared to flow in unlined glass tubes. The present study was devised to determine the effect of endothelial cell layer on blood flow in vessels under in vitro conditions in which pressure--flow relationships can be monitored precisely. Monolayers of human endothelial cells were grown over the major portion of the inner surface of glass tubes (I.D. = 1130 microns, length = 7.5 cm), and differential pressure and flow in the tubes were measured for plasma and suspensions of erythrocytes in plasma. Controls of phosphate buffer solution and culture medium were used to calculate inner diameters for both tube types. Results show statistically insignificant differences between apparent viscosities calculated from pressure-flow data in unlined and endothelial cell-lined tubes. These data indicate that the presence of endothelial lining does not have a marked influence on apparent viscosity of either blood or plasma when flowing through tubes of this diameter.

Animals↗
PubMed1981

Electroviscous flow and electrophoretic motion during erythrocyte entry in a glass capillary in the presence of applied electric potential gradients.

One means of measuring an effect of erythrocyte deformability on red cell flow is to determine how long it takes erythrocytes to enter or flow through an aperture whose diameter is smaller than 8 micrometers. It is convenient to impose an electric potential difference across the aperture so that the passage of an erythrocyte can be monitored by electronic means. We report here that such electric potential gradients may have a large influence on red cell entry times, primarily through the mechanism of erythrocyte electrophoretic mobility.

Electrophoresis↗
PubMed1981

Vascularity of gastrointestinal staple lines demonstrated with silicone rubber injection.

Gastrointestinal stapling devices were applied across canine small intestine, and then the blood supply of the stapled segments was immediately filled with silicone rubber. After tissue clearing and microdissection, the outstanding vascularity of the staple lines was clearly demonstrated. The B configuration of the closed staple allows blood vessels of substantial size to pass through it. This might make staple technique especially advantageous whenever vascularity is critical.

Animals↗
PubMed1981

Dynamics of erythrocyte motion in filtration tests and in vivo flow.

The characteristics of low haematocrit erythrocyte suspension flow through the 5 micrometer pores of a nuclepore filter, under low pressure drops, are compared to those of red cell flow through the human spleen. (a) For suspension filtration when the haematocrit is less than 1.5% and the pressure drops are less than 1 cmH2O, the characteristic RBC transit time through a 5-micrometer pore filter is about 10 ms, with an overall average velocity of about 1 mm/s, with the fraction of the unplugged filter pores occupied by RBC about 3.5 times the haematocrit of the filtrate. (b) In the human spleen, the mean residence time in the red pulp is about 66 s or longer, with an average velocity of 0.25 micrometer/s or less. During transit through the sinus wall slits (about 1 micrometer by 6 micrometer rectangular openings, about 2 micrometers long, residence time is estimated to be 10 s or longer. Considering the differences in these flow situations (and assuming the human spleen provides the critical in vivo RBC deformability test), it would seem necessary to demonstrate parallelism of the results of the in vitro and in vivo tests.

Arteries↗
PubMed1981

The measurement of lymphocyte volume: importance of reference particle deformability and counting solution tonicity.

We have determined the influence of reference particle deformability and suspending buffer tonicity on the measurement of lymphocyte volume by an electronic particle volume analyzer. When the volume analyzer was standardized with latex spherules having a shape factor (fe) of 1.5, red cell volume was 96 cu micron and lymphocyte volume was 289 cu micron. The red cell volume corresponded closely to the true red cell volume; the true lymphocyte volume, however, was 218 cu micron when measured by the lymphocytocrit/lymphocyte count and 203 cu micron by wet lymphocyte weight and density (mean approximately 210 cu micron). The difference between the electronic volume (Ve) of 289 cu micron and true lymphocyte volume of 210 cu micron was due to the influence of lymphocyte deformability (shape factor) as it traverses the sizing aperture. Since the true volume equals the Ve/fe, the red cells with a shape factor near 1.0 were sized appropriately by this method. In contrast, the lymphocyte shape factor was 1.38; thus, the true lymphocyte volume was 289 cu micron/1.38 or 210 cu micron. The tonicity of the suspending solution also influenced the measurement of particle volume when osmotically inactive standard particles (e.g., latex spherules) were used as a reference. Whereas the true lymphocyte volume was 210 cu micron at 286 mosmole/liter, it was 194 cu micron at 330 and 229 cu micron at 250 mosmole/liter. The standard counting solution, Isoton, is hyperosmolar (330 mosmole/liter) and causes an 8% shrinkage of osmotically active cells.

Buffers↗
PubMed1968

Rheological comparison of hemoglobin solutions and erythrocyte suspensions.

Hemoglobin solutions prepared from hemolyzed human erythrocyte packs have Newtonian flow properties. Diluted solutions are also Newtonian. All solutions have a viscosity lower than the apparent viscosity of erythrocyte suspensions of equal oxygen-carrying capacity. The presence of cell debris in hemoglobin solutions causes non-Newtonian (pseudoplastic or rheopectic) flow behavior.

Blood Viscosity↗
PubMedDate not supplied

Model studies of leukocyte-endothelium-blood interactions. II. Hemodynamic impact of leukocytes adherent to the wall of post-capillary vessels.

Computational fluid dynamics (CFD) and large scale model experiments were used to analyze the hemodynamic impact of leukocytes adherent to the wall of post-capillary venules. Using a large scale model and, with the aid of a finite element package, solving the Navier Stokes equations for low Reynolds number flow in a cylinder past an adherent sphere, we have developed a dimensionless correlation which permits the estimation of the pressure drop across an adherent leukocyte in an in vivo vessel. This relationship is: f.Re = exp[2.877+4.630 (d/D)4] where f is the Fanning friction factor, Re is the Reynolds number and d/D is the leukocyte to vessel diameter ratio. The friction factor is proportional to the pressure drop across the leukocyte, and does not significantly increase until d/D is greater than 0.5, and then increases rapidly with increasing d/D. Computations indicate that the length of the disturbed flow region generated by an adherent leukocyte increases with decreasing vessel size. The average wall stress in the disturbed flow region remains constant, and equal to the wall stress in the undisturbed region for d/D less than approximately 0.5. For d/D greater than 0.5, the average wall stress in the disturbed flow region increases rapidly with increasing d/D. There is an even larger increase, up to five times greater than the average disturbed stress, in the peak wall stress in the disturbed flow region. This indicates that significant wall stress gradients can be generated by an adherent leukocyte in post-capillary size vessels.

Cell Adhesion↗