Platelet activation in a circulating flow loop: combined effects of shear stress and exposure time

Abstract

Measurement of small changes in platelet activation state (PAS) in circulating stenotic systems in vitro has been problematic because of a paucity of real-time assay methods and circulation systems of low platelet-activating potential. PAS was measured by a modified prothrombinase assay in which activated platelets provide the essential cofactors in the activation of prothrombin by factor Xa. Chemical modification of the prothrombin ensures that the thrombin produced, while assayable, does not activate platelets. Human platelets were circulated in loops in which exposure to shear stress was adjusted by independently varying flow rate, viscosity, and the time of exposure to shear. Although with some differences in platelet response to different conditions of stress, the PAS directly increased with time of circulation, shear stress, and time of exposure to shear. The results show that low-level platelet activation caused by shear stress in a circulation loop can be quantitatively assessed in near-real time in a system of tube geometry. They confirm previous results obtained in non-circulating systems that exposure of platelets to shear conditions on the same order as found in the vasculature causes significant platelet activation, and that this activation is dependent on both shear stress and time of exposure.

DPIV Prediction of Flow Induced Platelet Activation—Comparison to Numerical Predictions

“…We have previously shown that PAS measurements correlate with flow cytometry of negative-phospholipid exposure measured by annexin V binding. 15 Informed consent was obtained from healthy adult volunteers of both sexes who had taken no aspirin or ibuprofen for two weeks. Blood, 30 ml, was drawn by venipuncture and collected into 0.3 ml 40% trisodium citrate.…”

“…Blood, 30 ml, was drawn by venipuncture and collected into 0.3 ml 40% trisodium citrate. Platelet buffer was then prepared and circulation experiments performed according to methods described by Jesty et al 15 . Recirculation studies were conducted at Re = 300 in a recirculation flow loop (Fig.…”

“…The differences in platelet activation rates (slopes of PAS activity vs. time) were analyzed for statistical significance as follows. The normalized data were fitted by linear regression, and the regression lines were then tested for difference in slopes according to a generalization of Student's paired t-test 15 and results were presented as the percentage of the maximal activation of the specific platelet preparation.…”

“…Shear stresses and flow patterns (fluid dynamics factors), and concentrations of coagulation factors and platelet agonists (biochemical factors) may lead to platelet activation and aggregation. Recently, it was shown, among other factors, that shear stress history rather than shear stress ranges, could determine hemodynamical platelet activation, 3,4,15 which may eventually increase thrombus formation. 19 Platelet responses have been identified under controlled experimental conditions.…”

Differences Between Mainstream and Sidestream Cigarette Smoke Extracts and Nicotine in the Activation of Platelets Under Static and Flow Conditions

“…15,16 Activated, but not unactivated, platelets contribute 2 essential cofactors in this reaction, negative phospholipid and factor Va. Thus, the rate of thrombin generation reflects the activation state of the platelets.…”