Surgery – Blood drawn and replaced or treated and returned to body
Reexamination Certificate
1999-07-09
2001-04-17
Mendez, Manuel (Department: 3763)
Surgery
Blood drawn and replaced or treated and returned to body
C604S006090
Reexamination Certificate
active
06217540
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a blood filter cartridge for the preparation of a plasma or serum sample from whole blood.
The type or concentration of blood components, such as metabolites, proteins, lipids, electrolytes, enzymes, antigens, and antibodies, is measured, in general, using a plasma or serum sample obtained by centrifuging whole blood. However, centrifuging takes labor and time. Particularly, centrifuging is unsuitable for an urgent case of measuring a small number of samples promptly and in site inspection, because of requiring a centrifuge and electricity. Thereupon, it has been investigated to separate serum from whole blood by filtration.
Several filtration methods using glass fiber filter have been developed wherein whole blood is charged into the glass fiber put in a column from one side of the column, and pressurized or evacuated to obtain plasma or serum from the other side (Japanese Patent KOKOKU Nos. 44-14673, 5-52463, Japanese Patent KOKAI Nos. 2-208565, 4-208856).
However, practical filtration methods capable of obtaining an amount of plasma or serum from whole blood necessary for measuring by an automatic analyzer have not been developed except for particular analytes, such as blood sugar.
On the other hand, the previously inventors developed a blood filter cartridge composed of a filter holder and a syringe. The filter holder is composed of a holder body which contains filter material and a cap which is screwed on the holder body. The filter material consists of, e.g., two sheets of glass fiber filter, one sheet of cellulose filter and one sheet of polysulfone microporous membrane (
FIG. 1
of EP 785430 A1)
Another blood filter cartridge composed of a holder body and a cap was also developed. The holder body consists of a plasma receiver located on the upper side and a filter chamber located on the underside. The filter material put in the filter chamber is composed of six sheets of glass fiber filter and one sheet of polysulfone microporous membrane (Example 1 of EP 785012A1).
The inventors further developed various blood filter cartridges, and their patent applications were made (Japanese Patent KOKAI 10-227788, 10-185909, 10-185780, etc.).
SUMMARY OF THE INVENTION
During repeated blood filtrations using blood filter cartridges having filtrate receivers previously developed by the inventors, the volume of the filtrate was sometimes abnormally low. The inventors first considered that the low volume of the filtrate occurred due to properties of blood, such as hematocrit value, but they found that the low volume of filtrate did not always correlate with any properties of blood. Thereupon, they further investigated the cause of the low volume, and found that, surprisingly, a part of the filtrate was being drawn back to the inside of the holder from the filtrate receiver immediately after the finish of filtration.
Thus, an object of the invention is to provide a blood filter cartridge which is made so that the filtrate discharged from the filtrate outlet will not be drawn back into the filtering chamber.
Then, the inventors investigated in order to develop a means for preventing the filtrate in the filtrate receiver from returning to the inside of the holder upon finishing filtration. The inventors found that the above drawing back problem of the filtrate can be resolved by reducing liquid holding ability around the filtrate outlet by either removing opposite faces which guide the filtrate to the receiver or making the length of the lower end of the filtrate outlet 0.8 mm or more, or by raising liquid releasing ability by either smoothing the surface around the filtrate outlet or using a material having a small surface energy around the filtrate outlet, to complete the invention.
Accordingly, the present invention is characterized by a blood filter cartridge which comprises a blood filtering material, a holder containing the blood filtering material and having a blood inlet and a filtrate outlet, and a filtrate receiver which receives the filtrate discharged from the filtrate outlet. The filtrate outlet is provided with a means for preventing the filtrate in the filtrate receiver from returning to inside of the holder upon finishing filtration. The means comprises, at least one of the following: removing opposite faces around the filtrate outlet, making the length of the lower end of the filtrate outlet 0.8 mm or more, smoothing the surface around the filtrate outlet, and forming the surface around the filtrate outlet by a material having a small surface energy.
It is considered that, in conventional blood filter cartridges, since blood filtrate is viscous, filtrate remains between the filtrate outlet and the liquid surface of the filtrate receiver in a certain thickness to form a bridge upon finishing blood filtration. When the filtrate existing on the inside of the filtrate returns to the filtering chamber, the returning filtrate draws the filtrate in the receiver back to the filtering chamber by the surface tension or siphon action through the bridge.
In the invention, the vanishment of the bridge is accelerated by removing a liquid holding member, by reducing liquid holding ability, by smoothing the surface around the filtrate outlet, or by forming the surface around the filtrate using a material having a small surface energy.
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patent: 4453927 (1984-06-01), Sinko
patent: 4775482 (1988-10-01), Thurman
patent: 4954251 (1990-09-01), Barnes et al.
patent: 5403273 (1995-04-01), Lindsay
patent: 5614105 (1997-03-01), Heilmann et al.
patent: 5736044 (1998-04-01), Proulx et al.
patent: 5979668 (1999-11-01), Kane et al.
patent: 5980759 (1999-11-01), Proulx et al.
Arai Takaki
Igarashi Takeshi
Ishizaki Keiichi
Ito Toshihisa
Kitajima Masao
Fuji Photo Film Co. , Ltd.
Mendez Manuel
Reed Smith LLP
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