Patent Application
20060191841
The present invention generally relates to a blood filter device used for filtering foreign substances, thrombi, and the like in an artificial heart-lung circuit. In particular, the present invention relates to a blood filter device configured so that air bubbles remaining in a filter can be removed easily and to a method of producing the same.
BACKGROUND ART
Nowadays, there has been a growing trend to incorporate a blood filter device such as an arterial filter in an artificial heart-lung circuit used for heart surgery involving extracorporeal circulation for the sake of safety. To provide adequate security for patients, it has been demanded strongly that such a blood filter device be configured so that it can remove minute foreign substances in the artificial heart-lung circuit, thrombi formed during an operation, or air that has entered or been released from the circuit so as not to allow them to enter the patient body.
A filter generally used in the blood filter device is a polyester screen filter with pores of about 20 to 40 μm that has been pleated and then formed into a cylindrical shape. For example, Japanese Patent No. 3270193 discloses that a sheet-like filter member is folded so as to have a plurality of pleats and the pleated filter member is then formed into a cylindrical shape in which the respective pleats are arranged radially with peaks thereof positioned on the outer circumference side and valleys thereof positioned on the inner circumference side. The thus-formed cylindrical filter is disposed in a cylindrical housing. In the filter configured as above, blood flows in the housing in the radial direction of the cylindrical filter member to pass therethrough, which allows dirt, impurities, thrombi, and the like contained in the blood to be removed effectively, as disclosed in Japanese Patent No. 3012692 and JP 2000-60967 A, for example.
In the filter as described above, blood first flows into an upper part of the cylindrical filter member, passes through the cylindrical filter member in its radial direction via an outer part of the filter member, and then flows out from a lower part of the cylindrical filter member via an inner part of the filter member. In this filter, the filter member surface extends vertically. This poses a problem in that, when a priming solution flows into the filter surface during a priming operation, air bubbles are liable to remain in the filter. Moreover, it is difficult to discharge the remaining air bubbles to the outside. This is because, since the filter member surface extends vertically, the air bubbles cannot be released from the filter easily, so that it takes quite a long time to remove the air bubbles completely.
More specifically, air bubbles remaining in the filter can be released with an impact from the outside caused by, for instance, flicking the housing with a finger. In this case, however, although the air bubbles can be released temporarily by giving an impact from a portion close to a position where the air bubbles adhere, they are liable to adhere again to an adjacent pleat of the filter. Thus, it is difficult to bring the air bubbles to an air vent provided above.
In order to solve the above-described problem, it is an object of the present invention to provide a blood filter device that can remove impurities, thrombi, and the like in blood effectively and also can discharge air bubbles remaining in a filter easily.
The present invention provides a blood filter device including: a housing that includes a dome portion forming an upper part of the housing, a filter retaining portion forming a middle part of the housing, and a bottom portion forming a lower part of the housing; an inlet provided on a lateral portion of the dome portion so as to allow blood to flow into the dome portion horizontally and along an inner wall of the dome portion; an air vent provided at a top of the dome portion; a filter for filtering a foreign substance in the blood, the filter being disposed in the filter retaining portion; and an outlet for the blood, the outlet being provided in the bottom portion. The blood filter device is configured so that the blood flows into the dome portion from the inlet, passes through the filter retaining portion, and then flows out from the outlet. The filter is formed of a sheet-like filter member that has been folded so as to have a plurality of pleats with enveloping surfaces connecting top ends of the respective pleats being flat so that the filter as a whole has a plate-shaped outer shape. The filter is arranged so as to partition a cavity of the housing into a dome portion side and a bottom portion side.
The present invention also provides a method of producing a blood filter device configured as above. First, a filter is formed by folding a sheet-like filter member so as to have a plurality of pleats with enveloping surfaces connecting top ends of the respective pleats being flat so that the filter as a whole has a plate-shaped outer shape. Then, the filter is disposed in a cavity of the filter retaining portion of the housing so that the flat enveloping surfaces extend horizontally. A space between an inner side wall of the filter retaining portion and an outer peripheral portion of the filter is filled with a resin while applying a centrifugal force that is caused by rotation around a center of the filter retaining portion and acts horizontally and then hardening the resin, thereby fixing the filter to the inner side wall of the filter retaining portion with the resin.
In the blood filter device according to the present invention, the filter is formed of a sheet-like filter member that has been folded so as to have a plurality of pleats with enveloping surfaces connecting top ends of the respective pleats being flat so that the filter as a whole has a plate-shaped outer shape, and the filter is disposed in the blood filter device so that the flat enveloping surfaces extend horizontally. With this configuration, air bubbles that remain on the filter surface during a priming operation can be removed easily by merely giving a physical impact to the housing, because there is no obstruction either above or below the filter.
The above-described blood filter device may be configured so that a space between an inner side wall of the filter retaining portion and an outer peripheral portion of the filter is filled with a resin so as to be sealed, and the filter is fixed to the inner side wall of the filter retaining portion with the resin. This allows the filter to be fixed reliably and also allows the space between the inner side wall of the filter retaining portion and the outer peripheral portion of-the filter to be sealed reliably.
It is preferable that the ratio h/r of a height h of the dome portion to an inner diameter r of the dome portion on a filter retaining portion side is in the range from 0.26 to 1.06. More preferably, the ratio h/r is in the range from 0.44 to 0.91. Also, it is preferable that the ratio d/r of a depth d of the bottom portion to the inner diameter r of the dome portion on the filter retaining portion side is in the range from 0.11 to 0.30.
Also, it is preferable that the inner diameter r of the dome portion on the filter retaining portion side is 27 to 33 mm and the height h of the dome portion is 7 to 35 mm. With this configuration, it is possible to secure a sufficient air bubble-trap amount. More preferably, the height h of the dome portion is 12 to 30 mm. Still more preferably, the depth d of the bottom portion is 3 to 10 mm. With this configuration, it is possible to achieve a suitable balance between air bubble-removing performance and an amount of blood required to fill the blood filter device. Alternatively, a distance between adjacent pleats of the filter may be set to 1.6 to 3.7 mm, and a height of each pleat may be set to 5 to 30 mm. This allows the removal of air bubbles after a priming operation to be carried out easily.
The filter can be formed only of a filter member having a function of filtering a foreign substance. Furthermore, the filter retaining portion may have a cylindrical cavity whose cross section taken in a horizontal direction is circular. Still further, an outer peripheral length of an internal space of the dome portion is reduced toward the top of the dome portion. Preferably, an inner surface of the bottom portion has no recess or protrusion.
In the method of producing a blood filter device according to the present invention, potting is performed while applying a centrifugal force so that the space between the inner side wall of the retaining portion inner cylinder and the outer peripheral portion of the filter is sealed with the resin. This allows a plurality of effects, such that the pleats of the filter can be bonded to each other, the pleats of the filter can be supported by the filter retaining portion, etc., to be obtained at the same time. Therefore, according to the production method of the present invention, the blood filter device can be produced with an extremely efficient production process.
In this production method, it is preferable that holding ribs that extend vertically are provided at positions on the inner side wall of the filter retaining portion corresponding to end portions of the respective pleats, and when disposing the filter in the cavity of the filter retaining portion, the end portions of the pleats are inserted to the holding ribs, respectively, so that the filter is temporarily held by the inner side wall of the filter retaining portion.
Also, it is preferable that, for forming the housing, an upper half and a lower half are provided that are to be joined to each other so that a joint between the upper half and the lower half is in the filter retaining portion of the housing, the filter is disposed in a portion corresponding to the cavity of the filter retaining portion in one of the upper half and the lower half, and the other one of the upper half and the lower half is joined to the one of the upper half and the lower half, and thereafter, the sealing and the hardening of the resin are performed.
Hereinafter, a blood filter device according to the present invention will be described by way of an embodiment with reference to the drawings
On a lateral portion of the dome portion 2, an inlet 5 is provided so as to allow blood to flow into the dome portion 2 horizontally and along an inner wall of the dome portion 2. On the top of the dome portion 2, an air vent 6 for discharging air such as air bubbles is provided. An outlet 7 for blood is provided in the bottom portion 4. The liquid that has flowed into the dome portion 2 from the inlet 5 passes through the filter retaining portion 3 and then flows out from the outlet 7. The bottom portion 4 also has a support portion 4a, which is used when installing the filter device and is irrelevant to the filtering function.
The dome portion 1 is formed so that an inner diameter thereof is reduced gradually toward the top of the dome portion 1. This allows air bubbles contained in blood to be released easily and the air bubbles thus released to move upward along the inner peripheral surface of the dome portion 1. Furthermore, since the dome portion 1 has a horizontal cross section of a circular shape and the inlet 5 is provided so as to allow blood to flow into the dome portion 2 horizontally and along an inner wall of the dome portion 2, the blood that has flowed into the dome portion 2 from the inlet 5 flows along the inner peripheral surface of the dome portion 2, thereby causing a swirling flow as indicated by the solid line in
The filter retaining portion 3 has a cylindrical shape. As shown in
In the state where the filter 8 is disposed as shown in
Furthermore, air bubbles that remain in the filter 8 when a priming solution passes through the filter 8 during a priming operation can be discharged easily from the air vent 6 at the top of the dome portion 2 or from the outlet 7 in the bottom portion 4 with an impact applied vertically to the filter 8 from the outside, for example, by flicking the bottom portion 4 with a finger. More specifically, because there is no obstruction either above or below the filter 8, air bubbles released from the filter 8 do not adhere to another portion of the filter 8 again, which ensures that they reach the air vent 6 at the top of the dome portion 2 or the outlet 7 in the bottom portion 4 and are discharged therefrom.
Furthermore, in the filter device according to the present embodiment, with the configuration in which the filter 8 as a whole has a plate-shaped outer shape with the enveloping surfaces connecting the top ends of the respective pleats being flat, the following effect also can be obtained. That is, since the filter 8 can maintain its shape well on its own, it is possible to form the filter 8 using only a mesh material as a filter member. In contrast, with a conventional configuration, it is necessary to use a support net in combination with the mesh material to maintain the shape of the filter 8. When the filter 8 is formed only of a mesh material without using a support net, air bubbles can be removed easily and besides, a loss of the blood flow pressure also can be reduced.
The bottom portion 4 provides a predetermined space under the filter 8. This allows a loss of the blood flow pressure passing through the filter device to be reduced to a negligible level in practical use. An inner surface of the bottom portion 4 is smooth and free from a projection or a recess. This allows the blood that has passed through the filter retaining portion 3 to be led to the outlet 7 without being impeded. Thus, the formation of thrombus or the like in the blood that has passed through the filter retaining portion 3 can be suppressed.
When the outlet 7 is provided in the lowest portion of the bottom portion 4 as shown in
As the filter member, it is possible to use a mesh material, a woven fabric, a non-woven fabric, or the like, or a combination of two or more of them, for example. The filter member can be made of polyester, polypropylene, polyamide, fluorocarbon fiber, stainless steel, or the like.
It is preferable that the housing 1, especially a horizontal cross section of the dome portion 2, has a circular shape because it is desired to cause a swirling flow of blood. However, it is to be noted here that other shapes such as an oval shape also can produce the same effect as described above. In the present embodiment, an inner diameter r (see
In addition to the above-described effect, the blood filter device according to the present embodiment also is advantageous in that it can be made smaller than conventional blood filter devices while maintaining the filtering function satisfactory in practical use. However, to this end, it is desirable to set parameters with regard to the shape of the cavity of the housing 1 and the shape of the filter 8 as follows. The parameters to be set are as follows: an inner diameter r of the dome portion 2, a height h of the dome portion 2, and a depth d of the bottom portion 4, which are shown in
First, the ratio h/r preferably is in the range from 0.26 to 1.06. If the ratio h/r is smaller than 0.26, an angle between an inner wall surface of the dome portion 2 and the horizontal plane is too small, so that sufficient air bubble-removing performance cannot be attained. On the other hand, if the ratio h/r is greater than 0.61, an amount of liquid required to fill the dome portion 2 is too great. More preferably, the ratio h/r is in the range from 0.44 to 0.91.
The ratio d/r preferably is in the range from 0.11 to 0.30. If the ratio d/r is smaller than 0.11, an angle between an inner wall surface of the bottom portion 4 and the horizontal plane is too small, so that sufficient air bubble-removing performance cannot be attained. On the other hand, if the ratio d/r is greater than 0.30, an amount of liquid required to fill the bottom portion 4 is too great.
Furthermore, from the viewpoint of an air bubble-trap amount, the inner diameter r of the dome portion 2 may be set to 27 to 33 mm, and the height h of the dome portion 2 may be set to 7 to 35 mm. By setting the inner diameter r and the height h dome portion 2 within these ranges, it is possible to achieve an air bubble-trap amount of at least 5 mL at a blood flow rate of 1.5 L/min, as required in practical use. It is more preferable to set the height h to 12 to 30 mm. Note here that the “air bubble-trap amount” is defined herein as an amount of air bubbles blocked by the filter 8 to be captured and accumulated in the dome portion 2 when a liquid for measuring this amount is supplied to the filter device. The method of measuring the air bubble-trap amount will be described later. In the following, an advantageous effect on an air bubble-trap amount obtained by setting the parameters as described above will be described.
First, as a precondition for setting the above-described parameters, a desirable filter membrane area will be described. A generally used blood filter for infants is required to have a maximum blood flow rate of 1.5 L/min in practical use. In order to restrict a pressure loss at this blood flow rate to a negligible level in practical use, a total area of pores in a mesh material that serves as a filter member needs to be substantially 8 cm2 or greater.
On the other hand, the mesh material generally has substantially uniform pores of 20 to 40 μm, and the porosity thereof desirably is 16% to 28%. When the porosity is less than 16%, the loss of the blood flow pressure is too great. On the other hand, when the porosity is more than 28%, the mesh material cannot remove a foreign substance, a thrombus, or the like that is 40 μm or larger, while such is a filtering function required in practical use. In order to allow the total area of the pores in the mesh material to be substantially 8 cm2 or greater as described above while satisfying the above-described porosity range, an area of the mesh material, i.e., the filter membrane, needs to be 29 cm2 to 50 cm2. Considering the variation in working conditions of the filter device, these values are multiplied by a safety factor 1.5. Therefore, the mesh material (the filter membrane) needs to have an area of 44 cm2 to 75 cm2.
Parameters that allow the filter device of the present embodiment to achieve an air bubble-trap amount satisfactory in practical use when the filter membrane area falls within the above-described range were examined through experiments. As a result of experiments conducted to determine the inner diameter r and the height h of the dome portion 2 that allow the filter device to achieve an air bubble-trap amount of 5 mL or greater at blood flow rate of 1.5 L/min, it was found that the inner diameter r should be 27 to 33 mm and the height h should be 7 to 20 mm as described above.
The air bubble-trap amount was measured in the following manner. As a liquid for measuring the air bubble-trap amount, citrated bovine blood (37° C., Ht.: 35%, T.P.: 6 g/dL) was supplied to the filter device shown in
When the area of the filter membrane and the inner diameter r and the height h of the dome portion 2 satisfy the above-described ranges, the volume of the filter device of the present embodiment can be reduced to about half the volumes of conventional filter devices.
With regard to the parameters other than those described above, it is desirable that the depth d of the bottom portion 4 is in the range from 3 to 10 mm, from the aspect of the amount of blood required to fill the blood filter device. The reason for this is as follows. First, in order to allow easy discharge of air bubbles in blood flowing in the filter device from the outlet 7 of the bottom portion 4, it is necessary that the depth d is at least 3 mm. Furthermore, in order to make the amount of blood required to fill the blood filter device not greater than 15 mL as required when treating infants, it is necessary that the depth d is not greater than 10 mm.
Furthermore, as parameters with regard to the pleats of the filter 8, a distance between adjacent pleats and a height of each pleat may be set in particular ranges in order to allow air bubbles to be removed easily. It is desirable that the distance between adjacent pleats is 1.6 to 3.7 mm and the height of each pleat is 5 to 30 mm. When the distance between adjacent pleats is smaller than 1.6 mm, air bubbles cannot be removed easily. On the other hand, when the distance between adjacent pleats is greater than 3.7 mm, it is difficult to obtain a sufficient filter membrane area. When the height of each pleat is smaller than 5 mm, it is difficult to obtain a sufficient filter membrane area. On the other hand, when the height of each pleat is greater than 30 mm, the volume of the filter retaining portion 3 increases accordingly, which may result in an increase in the amount of blood required to fill the blood filter device.
Next, a method of producing the filter device according to the present embodiment will be described with reference to
These drawings show basically the same configuration as described above, but holding ribs 10 for supporting the filter 8 temporarily also are shown in these drawings (see
As shown in
In the retaining portion inner cylinder 3a of the upper half 1a, a pair of notches 11a further is formed. In the retaining portion outer cylinder 3b of the lower half 1b, through holes 11b are formed at positions corresponding to the pair of notches 11a formed in the retaining portion inner cylinder 3a. When the upper half 1a is fitted into the lower half 1b, the notches 11a communicate with the through holes 11b, thereby forming holes that pass through peripheral walls of the retaining portion inner cylinder 3aand the retaining portion outer cylinder 3b . The reason for providing these holes will be described later.
In the production of the blood filter device, the upper half 1a and the lower half 1b of the housing and the filter 8 are formed first in the above described manner. Then, as shown in
Thereafter, the upper half 1a and the lower half 1b are joined together by fitting the retaining portion inner cylinder 3ainto the retaining portion outer cylinder 3b , thereby obtaining the housing 1 as a single component.
Next, as shown in
When the rotating jig 12 is rotated, the filter device is subjected to a centrifugal force that is caused by rotation around a center of the filter retaining portion 3a and acts horizontally. As a result, the sealing resin spills out of the resin reservoir 13 to be supplied to the retaining portion inner cylinder 3a through the resin supply channel 14, so that a space between an inner side wall of the retaining portion inner cylinder 3a and an outer peripheral portion of the filter 8 is filled with a resin. By hardening the resin filling the space, the filter 8 can be fixed to the inner side wall of the retaining portion inner cylinder 3a with the sealing resin 9, as shown in
When the space between the inner side wall of the retaining portion inner cylinder 3a and the outer peripheral portion of the filter 8 is sealed with the resin by performing potting while applying a centrifugal force as described above, the following six effects can be obtained at the same time:
(1) the shape of the pleats of the filter 8 is maintained;
(2) the pleats of the filter 8 are supported by the filter retaining portion 3;
(3) the-holding ribs 10 are embedded in the resin;
(4) the upper half 1a and the lower half 1b of the housing are bonded to each other;
(5) the space between the inner side wall of the filter retaining portion 3 and the outer peripheral portion of the filter 8 is sealed; and
(6) the flow path is allowed to have a cross section such that there is no stepped portion at the boundary between the filter retaining portion 3 and the dome portion 2 or between the filter retaining portion 3 and the bottom portion 4.
Therefore, this production method can produce the filter device with an extremely simple process and thus is effective in reducing the production cost. Furthermore, the effect described in (3) contributes to the improvement of air bubble-removing performance. Moreover, by the effect described in (6), the inner wall surface of the housing can be made smooth, which contributes to the prevention of thrombus formation and to the improvement of air bubble-removing performance.
Note here that in the above-described production process, it is not always necessary to provide the holding ribs 10 in order to allow the filter 8 to be temporarily held by the inner side wall of the retaining portion inner cylinder. The filter 8 can be temporarily held by the inner side wall of the retaining portion inner cylinder 3a with other configurations.
Moreover, the way of folding the filter 8 is not limited to that shown in
Although the filter 8 is folded so as to have a plurality of pleats, the present invention is not limited thereto. For example, the filter as shown in
Industrial Applicability
According to the blood filter device of the present invention, foreign substances, thrombi, etc. in blood can be removed reliably, and besides, air bubbles adhering to an upper surface of the filter can be removed easily with a physical impact caused by, for example, hitting the housing from above or below the housing.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2003-081092 | Mar 2003 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP04/03835 | 3/22/2004 | WO | 9/21/2005 |
