Biorheology - Volume 25, issue 3

Article Type: Editorial

DOI: 10.3233/BIR-1988-25321

Citation: Biorheology, vol. 25, no. 3, pp. I-III, 1988

Authors: Copley, Alfred L. | Silberberg, Alex

Article Type: Editorial

DOI: 10.3233/BIR-1988-25301

Citation: Biorheology, vol. 25, no. 3, pp. 403-405, 1988

Authors: Copley, Alfred L. | Silberberg, Alex

Article Type: Other

DOI: 10.3233/BIR-1988-25302

Citation: Biorheology, vol. 25, no. 3, pp. 407-408, 1988

Authors: Copley, Alfred L.

Article Type: Obituary

DOI: 10.3233/BIR-1988-25303

Citation: Biorheology, vol. 25, no. 3, pp. 409-427, 1988

Authors: Isogai, Yukihide

Article Type: Obituary

DOI: 10.3233/BIR-1988-25304

Citation: Biorheology, vol. 25, no. 3, pp. 429-433, 1988

Authors: Ohayon, J. | Chadwick, R.S.

Article Type: Research Article

Abstract: The mechanical effects resulting from the normal transmural delay of electrical depolarization of the myocardium are investigated. An activation sequence having a finite radial propagation velocity is introduced into the equations of ventricular mechanics. The resulting system of coupled integral equations is solved using a perturbation method based on the small ratio of transmural propagation time to cardiac period. Numerical calculations are performed using cavity pressure and volume waveforms characteristic of the canine left ventricle (LV), for both simultaneous and delayed activation of fiber layers. The results show that a finite transmural electrical propagation velocity tends to: (i) equalize the …transmural distribution of sarcomere length during systole; (ii) equalize the transmural distribution of fiber external work/vol; and (iii) insignificantly affect myocardial tissue pressure. Calculations are also performed to investigate the mechanical effects resulting from the application of an externally applied moment that prevents LV torsion. Those results are highly dependent on the transmural distribution of sarcomere length in the stress-free reference state (unloaded diastole). When we assume a uniform distribution, then normal torsion acting with normal activation delay tends to: (i) increase the magnitude of fiber strain in the subendocardium and decrease it in the subepicardium; (ii) equalize the transmural distribution of fiber external work/vol; and (iii) lower myocardial tissue pressure. The normally occurring transmural delay of activation tends to lessen endocardial O2 demand, while the normally occurring torsion further lessens that demand and improves O2 supply. Show more

Keywords: Models, Theoretical, Models, Cardiovascular, Myocardial Contraction, Stress, Mechanical, Torsion, Heart Ventricle

DOI: 10.3233/BIR-1988-25305

Citation: Biorheology, vol. 25, no. 3, pp. 435-447, 1988

Authors: Sutera, S.P. | Nowak, M.D. | Joist, J.H. | Zeffren, D.J. | Bauman, J.E.

Article Type: Research Article

Abstract: Described is a special purpose cone-plate viscometer that is capable of acceleration or deceleration through a step change in speed in less than 0.7s. The speed of the rotating cone is controlled by a microcomputer which can be programmed to generate speed vs time ramp functions of variable slope. Prior calibration of motor power required to shear Newtonian fluids of known viscosity at various speeds provides the basis for determination of apparent suspension viscosity and enables the viscometer automatically to compensate for changing sample viscosity during shear. The viscometer was used to carry out a series of preliminary studies in …which platelet-rich plasma (PRP) was subjected to continuous and pulsatile shear stress at 37°C. Shear-induced platelet aggregation (SIPAG) was significantly greater in response to pulsatile versus continuous shearing except at the lowest applied stress (10 dyn/cm2 ). Increases ranged from about 40 percent at a stress amplitude of 25 dyn/cm2 to nearly 55 percent at dyn/cm2 . This increasing trend with stress amplitude might be interpreted as a positive correlation between SIPAG and the loading rate. Dense granule release, as indicated by serotonin release, was dependent on both stress amplitude and number of pulses even at the higher stress where SIPAG was independent of pulse number. Show more

Keywords: platelets, pulsatile shear stress

DOI: 10.3233/BIR-1988-25306

Citation: Biorheology, vol. 25, no. 3, pp. 449-459, 1988

Authors: Nomura, Hideshi | Ishikawa, Chiharu | Komatsuda, Teruhiko | Ando, Joji | Kamiya, Akira

Article Type: Research Article

Abstract: To study the effect of fluid shear stress on cultured endothelial cells, we have developed an apparatus for the stress creation, which consists of a stainless steel disk driven by an electric DC motor and a stage to place a culture dish and to adjust the distance between the disk and the dish. When the disk is rotated, a concentric fluid movement occurs in the culture medium in the dish and exerts the shear stress on the endothelial cells cultured on the bottom of the dish. A theoretical analyses concerning the induced concentric flow velocity predicted that when the angular …velocity of the disk rotation (ω ) is slow enough to maintain a Reynolds’ number of the order of 10, the exerted wall shear stress τ w on the endothelial cell monolayer is given for a constant as τ w = μ r ω / d where μ is the viscosity of the medium, d the distance from the plate to the monolayer and r the radial distance from the center of the dish. When ω is varied in a sinusoidal mode τ w also becomes sinusoidal, thus allowing to apply a pulsatile stress. In vitro experiments carried out to examine the validity of the theoretical results, using a suspension of polystyrene as a tracer with the ordinary culture medium and 99% ethanol, revealed excellent agreement of the measured velocity profiles with the predicted ones. The results demonstrated that the present apparatus can create both the steady and pulsatile wall shear stress on the culture cell layer as expected, unless Reynolds’ number greatly exceeds the level of 10. Show more

Keywords: shear stress, cell culture, endothelial cell, rotating plate, steady flow, pulsatile flow

DOI: 10.3233/BIR-1988-25307

Citation: Biorheology, vol. 25, no. 3, pp. 461-470, 1988

Authors: Gaspar-Rosas, A. | Thurston, G.B.

Article Type: Research Article

Abstract: Both the transmission of light through a confined layer of blood and the reflection from the surface of that layer have been utilized for studying the rheology of erythrocyte aggregates. The two methods do not necessarily provide the same information. The light reflected from the blood layer relates to the rheological behavior of erythrocytes near the blood surface, whereas the light transmitted relates more to the properties of blood in bulk. This investigation makes direct comparison between the transmitted and reflected light methods with regard to the kinetics of aggregation in thin and thick layers of blood as well as …following shear flow excitation steps of different sizes. Also, the transmission and reflection for static blood layers of varying thicknesses were determined. The kinetics of aggregation from transmitted and reflected light measurements are compared both graphically and by equations containing multiple characteristic aggregation times. The number of characteristic times required for accurate description increases with the time over which the aggregation process is monitored. The first 40 seconds of the aggregation process are precisely described by two characteristic times. For normal blood the characteristic times from reflection measurements are shorter than those from transmission measurements. Show more

Keywords: Erythrocyte aggregation, light transmission, light reflection, kinetics of aggregation, optical attenuation in blood, characteristic aggregation times

DOI: 10.3233/BIR-1988-25308

Citation: Biorheology, vol. 25, no. 3, pp. 471-487, 1988

Authors: Ovadyahu, D. | Eshel, D. | Priel, Z.

Article Type: Research Article

Abstract: Ciliary metachronism and motility were examined optically in tissue cultures from frog palate e:Rithelium as. a func.tion of extracellular ATP concentration in the range of 10−7 –10−3 M. The main findings were: a) upon addition of ATP the metachronal wavelength increased by a factor of up to 2. b) the velocity of the metachronal wave increased by a factor of up to 5. c) the frequency of ciliary beating increased by a factor of up to 2–3, the increase being temperature insensitive in the range of 15°C–25°C. d) the area under the 1-second FFT spectrum decreased by a factor of …up to 2.5. e) the energy of the metachronal wave is increased by a factor of up to 9.5. f) all the spectrum parameters are subject to influence by ATP, as also by ADP and AMP. However, there are pronounced differences in the various responses to them. Based on these findings, physical aspects of the rate increase of particle transport caused by addition of extracellular ATP are explained. A plausible overall chemical mechanism causing pronounced changes in ciliary motility is discussed. Show more

Keywords: Ciliary frequency, metachronal wavelength, metachronal velocity, mucociliary transport, extracellular ATP, metachronism

DOI: 10.3233/BIR-1988-25309

Citation: Biorheology, vol. 25, no. 3, pp. 489-501, 1988