Surgery – Truss – Pad
Patent
1995-06-15
1997-09-02
Cohen, Lee S.
Surgery
Truss
Pad
128632, 128760, 128692, A61B 500
Patent
active
056621078
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The invention concerns a device and a method for measuring the tendency to form blood clots in vitro by using non-anticoagulated venous blood which is pumped through one or more parallel synthetic channels with different diameters, "thrombogenesis units", which simulate in vivo bloodstream conditions, and where the fluid pressure is recorded before and after the thrombogenesis units, and the pressure drop is calculated as a function of the flow time, which will be an expression of how quickly a thrombosis is formed in the system.
DESCRIPTION OF THE PRIOR ART
The blood contains red and white blood corpuscles, plasma proteins and blood platelets and circulates in a closed circuit where the heart supplies the energy which impels the blood through the arterial part of the circuit. The consequences of clogging of this circuit vary in severity, depending on whether the peripheral circulation, cardial, pulmonary or cerebral circulation is affected. A considerable number of people in the industrialized part of the world are disabled or die due to circulatory disturbances and it is therefore vital from the social and economic points of view to be able to detect as early as possible the onset of possible circulatory problems, e.g. a thrombogenetic tendency, under different conditions and to monitor antithrombotic treatment.
To transport blood through a blood vessel, from a point A to a point B, the pressure in A (P.sub.A) must be greater than the pressure in B (P.sub.B). The blood flow from A to B, Q, is dependent on P.sub.A -P.sub.B and the resistance R to the flow, according to formula I; ##EQU1##
In an undamaged blood vessel the blood flow will be laminar and in accordance with Poiseuille's law, expressed in formula II; ##EQU2## where r=radius of the vessel
It can be seen in formulae I and II that the resistance can thereby be expressed by III; ##EQU3##
This shows that the resistance to the flow is affected by characteristics of the blood vessel (length and radius) together with the viscosity of the blood. In a vessel the flow profile will describe a parabolic shape, the layers which are closest to the wall of the vessel will adhere to the wall, while towards the middle of the stream the liquid layers will slide towards one another and the viscosity alone affects the flow picture. Thus the shear rate will be highest at the wall (see below).
With an increase in the speed of the blood the flow will remain laminar, and thus comply with Poiseuille's law, until a critical speed is reached, above which the flow becomes turbulent. In this state Osborne Reynolds demonstrated that the energy which drives the fluid is mainly used to create kinetic energy and the resistance to the flow will now depend on the density of the fluid instead of its viscosity, as was the case when the flow was laminar. The combination of turbulence and reduced vessel diameter will increase the resistance and lead to an increased drop in pressure over a vessel area in which there is a constriction.
Thrombosis can arise as a result of activation of blood platelets with a resultant aggregation of these and/or coagulation of blood which includes blood platelet activation, the formation of prothrombin activator which in turn catalyzes the formation of thrombin from prothrombin.
This thrombin thereafter catalyzes the conversion of fibrinogen into filaments of fibrin, which form a network and entrap blood platelets, blood cells and plasma thus forming a coagulum. Coagulation and blood platelet deposits are initiated amongst other things by damage to the vascular surface, collagen fibres in the vessel wall and damaged endothelial cells. The formation of thrombi, which is partly responsible for circulatory disturbances, often with disabling or fatal results, can be activated by an uneven endothelial surface, as in the case of arteriosclerosis, infections or trauma. Similarly, a very slow blood flow can be subject to coagulation since small amounts of thrombin and other procoagulants are constantly being formed. The thrombi, whic
REFERENCES:
patent: 4780418 (1988-10-01), Kratzer
patent: 5275953 (1994-01-01), Bull
Arterioscleriosis, vol. 10, No. 2, 1990 by Kjell S. Sakariassen et al. "Collagen Type III Induced Ex Vivo Thrombogenesis in Humans".
Carter Ryan
Cohen Lee S.
Nycomed Imaging AS
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