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Biomedical subjects

E F Grabowski

Publications and source records attributed to E F Grabowski.

48 records · Page 3Linked to original sources
PubMed1977

Thermal excitations of a bilipid membrane.

Propagating modes of vibration of a bilipid membrane have been detected with light beating spectroscopy. The dependence of omega on q is consistent with a model of a fluid film of surface tension sigma = 2.5 +/- 0.5 dyn cm-1 surrounded by a medium with rho = 1 g cm-3 and eta = 1.01 X 10(-2) P.

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PubMed1977

Platelet adhesion to foreign surfaces under controlled conditions of whole blood flow: human vs rabbit, dog, calf, sheep, pig, macaque, and baboon.

Our results reveal significant differences between mammalian species with respect to platelet adhesion to foreign surfaces exposed to heparinized, flowing blood. In particular, we have demonstrated the following: 1) At a surface shear rate characteristic of shear rates in mammalian arteries, human platelet adhesion (and that of calf, baboon, macaque, hog or sheep) is negligible in comparison to dog or rabbit platelet adhesion after 10 mins of blood flow. 2) The species differences are biomaterial dependent: the human-dog difference is present with Cuprophan or Avcothane, but absent with compressed Gore-Tex or fluorinated ethylcellulose. (The platelets of humans and dogs adhere to comparable degrees on the latter 2 biomaterials.) 3) With Cuprophan and recirculated blood, the human-dog difference persists at 30 and 180 mins. 4) By means of videomicroscopy, the species differences are unlikely only to be an artifact of the possible formation and embolization of surface-adherent aggregates. Tests for the thromboresistance of candidate biomaterials and for platelet adhesion under controlled flow conditions must therefore begin to take into account differences between humans and other species.

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PubMed1976

Human vs. dog platelet adhesion to Cuprophane under controlled conditions of whole blood flow.

It is commonly assumed that a candidate biomaterial to which nonhuman (especially dog) platelets do not readily adhere is promising for human use. This assumption has been tested in a lucite chamber in which Cuprophane membrane (Bemberg PT-150), comprising one of the chamber surfaces, is exposed to citrated or heparinized flowing dog or human blood for 10 or 20 minutes and flowing buffer for 1 minute. Following exposure, membrane specimens are carefully removed, fixed in glutaraldehyde, and mounted on a slide. Platelets at a particular axial location are counted by phase-contrast microscopy (625 X). At a shear rate of 986 sec.-1 and at 10 minutes, platelets per square millimeter (mean +/- S.E.(N) in citrate were 28,400 +/- 5,000 (6), dog; 18 +/- 3.8 (4), human. Under the same conditions, platelets per squar millimeter in heparin were 32,600 +/- 8,400 (4), dog; 7.6 +/- 1.0 (3), human. A qualitatively similar species difference was found in citrate at one shear rate and at one other exposure time. Those observations suggest that evaluations of candidate human biomaterials carried out with dog (and perhaps other nonhuman) blood must be interpreted with caution.

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PubMedDate not supplied

Thrombolysis, flow, and vessel wall interactions.

Vascular endothelium remains a dynamic interface between blood, blood platelets, and the vessel wall. New developments make clear that many antithrombotic and prothrombotic responses of the endothelium depend on flow conditions in an adaptive manner: duration of a certain level of shear stress matters as well as level of shear. In general, over the course of several hours, endothelium appears to be more actively antithrombotic under moderate shear conditions (eg, 15 dyne/cm2) and more fibrinolytic under high shear conditions (eg, 30 dyne/cm2). Pulsatile flow and cyclic wall stress further modify these responses. Special consideration, moreover, must be given to branch points and regions of irregular geometry (ie, stenoses, aneurysms) in the circulation. In such locations-predilection sites for thrombosis, lipid uptake, and atherosclerosis-low levels of shear stress (eg, 0.5 dyne/cm2), large gradients in shear stress, and vessel wall bending stresses all become important. Preliminary work suggests that endothelial cells in such regions can become prothrombotic, leading to localized platelet adhesion/aggregation and fibrin formation on subendothelium and perhaps deeper structures following vessel injury. Flow effects on thrombolysis remain largely unstudied.

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