THROMBOSIS RESEARCH Printed in the United
A RHEOLOGICAL PLATELET
METHOD
AGGREGATION UNDER
H.J.
vol. States
KLOSE,
FOR
THE
(PA)
DEFINED
QUANTIFICATION
IN VITRO
FLOW
7, pp. 261-272, Pergamon Press,
AND
ITS
1975
Inc.
OF KINETICS
CONDITIONS
Dept. Pediatrics, University of Munich,
H. RIEGER and H. SCHMID-SCHUNBEIN, Dept. Physiology, RWTH Aachen, GERMANY (Received 17.3.1975; in revised form 26.5.1975. Accepted by Editor N. Goossens) ABSTRACT In viva, the processes of platelet aggregation and adhesion occur under conditions of rapid blood flow. However, most in vitro tests of platelet aggregation have not reconciled this basic fact of platelet physiology. A method has therefore been developed in which the platelet aggregation (PA) can be quantified in numerical terms under defined conditions of viscometric flow. Platelet rich plasma (PRP) is subjected to variable shear rates in a cone plate chamber, the resulting aggregation is recorded as a function of the incident rate of shear and/or shear time. After preliminary studies in which different constant shear rates were applied consecutively, an automatic device was designed which produces a continuous augmentation of shear rates and/or shear stresses in one single experiment (4,5-115 set 1). The minimum shear rates producing an arbitrary threshold aggregation is considered to be inversely related to the platelet aggregability, the maximum extent of PA in high shear flow is taken as a measure of the mechanical integrity of the resulting PA. As demonstrated, platelet aggregability and mechanical integrity of PA are subject to different experimental factors. The method is capable of numerical differentiation between hyperand hypofunction of platelets as occurring spontaneously, following drug application both in vivo and in vitro. INTRODUCTION Microscopic observation of the formation of a platelet plug in a vessel, reveals that the processes of platelet 261
PLATELET AGGREGATION & KINETICS
262
v01.7,~0.2
adhesion to the vessel wall and to other platelets only occur in blood which is rapidly flowing. In accordance, BEGENT and BORN (3), ARFORS
(1)
and BAUMGARTNER (2) found
an increased growth rate of hemostatic plugs or platelet adhesions, respectively, with increasing blood flow velocity. From the rheological point of view, great differences in the velocity of the neighbouring fluid layers at the vessel wall and at the surface of a growing thrombus have to be assumed, so that high local shear rates and shear stresses must be expected. Since the calculation of shear stresses and shear rates in vessels in vivo is highly complicated, investigation of the effect of these rheological parameters on platelet aggregation is best performed in vitro, where exact shear rates and shear stresses can be applied. DINTENFASS (7) was the first to study platelet aggregation in defined viscometric flow situations as a function of shear rates in non-anticoagulated blood. Using a viscometer he showed that during the blood coagulation process, platelet aggregation and white thrombus formation only occur when the blood is flowing with high shear rates. His assumption, that high shear conditions would accelerate the fibrin formation as well, has not been unequivocally confirmed
(19).
By microscopic examination of the coagulation
process, fibrin polymerisation and the process of the PA can be separated experimentally: the extent of the PA was greater with increasing shear rates and did not occur at low shear rates
(
A RHEOLOGICAL PLATELET
METHOD
AGGREGATION UNDER
H.J.
vol. States
KLOSE,
FOR
THE
(PA)
DEFINED
QUANTIFICATION
IN VITRO
FLOW
7, pp. 261-272, Pergamon Press,
AND
ITS
1975
Inc.
OF KINETICS
CONDITIONS
Dept. Pediatrics, University of Munich,
H. RIEGER and H. SCHMID-SCHUNBEIN, Dept. Physiology, RWTH Aachen, GERMANY (Received 17.3.1975; in revised form 26.5.1975. Accepted by Editor N. Goossens) ABSTRACT In viva, the processes of platelet aggregation and adhesion occur under conditions of rapid blood flow. However, most in vitro tests of platelet aggregation have not reconciled this basic fact of platelet physiology. A method has therefore been developed in which the platelet aggregation (PA) can be quantified in numerical terms under defined conditions of viscometric flow. Platelet rich plasma (PRP) is subjected to variable shear rates in a cone plate chamber, the resulting aggregation is recorded as a function of the incident rate of shear and/or shear time. After preliminary studies in which different constant shear rates were applied consecutively, an automatic device was designed which produces a continuous augmentation of shear rates and/or shear stresses in one single experiment (4,5-115 set 1). The minimum shear rates producing an arbitrary threshold aggregation is considered to be inversely related to the platelet aggregability, the maximum extent of PA in high shear flow is taken as a measure of the mechanical integrity of the resulting PA. As demonstrated, platelet aggregability and mechanical integrity of PA are subject to different experimental factors. The method is capable of numerical differentiation between hyperand hypofunction of platelets as occurring spontaneously, following drug application both in vivo and in vitro. INTRODUCTION Microscopic observation of the formation of a platelet plug in a vessel, reveals that the processes of platelet 261
PLATELET AGGREGATION & KINETICS
262
v01.7,~0.2
adhesion to the vessel wall and to other platelets only occur in blood which is rapidly flowing. In accordance, BEGENT and BORN (3), ARFORS
(1)
and BAUMGARTNER (2) found
an increased growth rate of hemostatic plugs or platelet adhesions, respectively, with increasing blood flow velocity. From the rheological point of view, great differences in the velocity of the neighbouring fluid layers at the vessel wall and at the surface of a growing thrombus have to be assumed, so that high local shear rates and shear stresses must be expected. Since the calculation of shear stresses and shear rates in vessels in vivo is highly complicated, investigation of the effect of these rheological parameters on platelet aggregation is best performed in vitro, where exact shear rates and shear stresses can be applied. DINTENFASS (7) was the first to study platelet aggregation in defined viscometric flow situations as a function of shear rates in non-anticoagulated blood. Using a viscometer he showed that during the blood coagulation process, platelet aggregation and white thrombus formation only occur when the blood is flowing with high shear rates. His assumption, that high shear conditions would accelerate the fibrin formation as well, has not been unequivocally confirmed
(19).
By microscopic examination of the coagulation
process, fibrin polymerisation and the process of the PA can be separated experimentally: the extent of the PA was greater with increasing shear rates and did not occur at low shear rates
(
