Pumps – Motor driven – Electric or magnetic motor
Reexamination Certificate
1999-02-26
2001-02-06
Leung, Philip H. (Department: 3742)
Pumps
Motor driven
Electric or magnetic motor
C415S206000
Reexamination Certificate
active
06183220
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a blood pump used for artificial auxiliary hearts and heart-lung machines, and more particularly to a blood pump capable of preventing thrombus from attaching to the interior thereof.
PRIOR ART
Conventionally, a centrifugal pump has been used as a blood pump. The centrifugal pump comprises a conical impeller for generating a centrifugal flow inside the housing thereof, a suction inlet, through which blood is, drawn, disposed near the rotation center portion of the impeller, a delivery outlet, through which blood pressurized by the impeller is discharged from the peripheral portion of the impeller, a motor disposed outside the casing to rotate the impeller, and a seal formed between the casing and the rotation shaft of the impeller. This pump is called a sealed type wherein the interior of the casing is maintained watertight by sealing.
Furthermore, U.S. Pat. No. 4,984,972 has proposed a seal-less type blood pump, wherein the impeller is rotated in a non-contacting condition by a rotating magnetic field outside the casing. The impeller is provided with magnetic material assigned to the magnetic field, and both ends of its rotation shaft are supported by pivot bearings attached inside the casing.
In the case of the above sealed type centrifugal blood pump, it is difficult to completely seal the clearance between the rotation shaft and the casing. As a result, the blood is apt to be clotted at this sealed portion, generating the so-called thrombus. Paticularly, The thrombus may grow in areas inside the casing where the flow rate of blood is dropped.
Furthermore, the seal-less type blood pump may also cause thrombus at the inner bottom portion of the casing on the opposite side of the suction inlet, although the pump has no sealing portion for the rotor of the impeller. In order to solve this problem, U.S. Pat. No. 5,399,074 proposes a blood pump of the seal-less type which is provided with through holes penetrated through the impeller up to the bottom side, or auxiliary vanes (or secondary vanes) projected from the bottom surface of the impeller, then enhancing the fluidity of the blood on the bottom of the casing.
However, no sufficient blood fluidity was obtained by just forming the through holes in the seal-less pump, and thrombus was unable to be prevented.
Furthermore, in the case when the auxiliary vanes were provided, thrombus was able to be prevented. However, this caused a problem of generating hemolysis, that is, hemocytes in blood passed through the pump were apt to be destructed. Hemolysis herein means a characteristic or an extent of hemocytes being apt to be destructed by the auxiliary vanes. Blood flows slowly and is apt to stay at the inner bottom portion of the casing in the blood pump, whereby thrombus is apt to be caused. When the auxiliary vanes are used, thrombus can be prevented by the stirring force of the auxiliary vanes. However, hemocytes are apt to be destructed at the same time.
SUMMARY OF THE INVENTION
In order to solve the above-mentioned problems peculiar to the above-mentioned centrifugal blood pumps, an object of the present invention is to provide a blood pump capable of substantially completely preventing thrombus from attaching to the inner bottom portion of the casing thereof without deteriorating the anti-hemolytic characteristic of blood.
In the present invention, one or more stirring elements having the shape of a fin or a groove are formed on the bottom of the main impeller facing the inner bottom surface of the pump casing. In the invention, the dimensions, shape and positions of the fins or grooves used as the stirring elements are determined to completely prevent thrombus from attaching to the inner bottom portion of the casing without deteriorating the anti-hemolytic characteristic of blood.
To attain this purpose, the dimensions, shape and positions of the stirring elements are defined using parameters of a ratio L/D of the entire length L of the fins or grooves to the diameter D of the impeller, and a ratio S/A of the surface area S of the blood contact surfaces of the fins or grooves to the projected area A of the impeller. The entire length L of the fins or grooves conforming to the shape of the impeller and the surface area S of the blood contact surfaces of the fins or grooves are determined in accordance with the parameters.
These parameters can be chosen to be in ranges where the normal anti-hemolytic characteristic of blood and nonattachment of thrombus are maintained, as follows.
0.43<L/D<1.30 (1)
and,
0.03<S/A<0.21 (2)
The two inequalities (1) and (2) relates to adequate force for stirring blood in the clearance between the bottom surface of the impeller and the inner bottom of the casing. If parameters L/D and SiA are both smaller than the lower limits in the ranges of the inequalities (1) and (2), respectively, the force stirring blood by the fins or grooves used as the stirring elements is so weak that thrombus is apt to attach to the inner bottom portion of the casing. If the parameters are larger than the higher limits in the range, the stirring force is so excessive that the amount of hemolysis increases because of destructed hemocytes, whereby the anti-hemolytic characteristic of blood is impaired.
REFERENCES:
patent: 4984972 (1991-01-01), Clausen et al.
patent: 5017103 (1991-05-01), Dahl
patent: 5290236 (1994-03-01), Mathewson
patent: 5360317 (1994-11-01), Clause et al.
patent: 5399074 (1995-03-01), Nose et al.
patent: 5575630 (1996-11-01), Nakazawa et al.
patent: 5658136 (1997-08-01), Mendler
patent: 5803720 (1998-09-01), Ohara et al.
patent: 5863179 (1999-01-01), Westphal et al.
Makinouchi Kenzo
Nose Yukihiko
Ohara Yasuhisa
Otsuka Goro
Takami Yoshiyuki
Fastovsky Leonid
Hogan & Hartson LLP
Kyocera Corporation
Leung Philip H.
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