Surgery – Respiratory method or device – Means for removing substance from respiratory gas
Reexamination Certificate
1998-02-25
2001-04-03
Weiss, John G. (Department: 3761)
Surgery
Respiratory method or device
Means for removing substance from respiratory gas
C128S200240, C128S205120, C128S205290, C210S445000, C055S511000
Reexamination Certificate
active
06209541
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to medical-surgical breathing filters, and is more particularly concerned with breathing filters that include electrostatic filter media.
Electrostatic breathing filters have been used since the early 1980s to filter breathing gases. The filter media consists of polypropylene fibers which have been made electrostatic by a corona discharge process. The fibers are needled so that they intertwine, thus forming a relatively flat filter pack which electrostatically captures particulate from gases moving through the filter's open passageways. Electrostatic filters are effective as bacteria and viral filters in medical device breathing filters, but are not considered to be HEPA filters. Their use can nevertheless be justified by their filtration effectiveness as well as by their relatively low cost. Electrostatic filter packs do not need to be hermetically sealed around their periphery as particulate is attracted and attaches to the surfaces of the fibers. It is only necessary that the construction of a filter housing containing an electrostatic filter pack includes internal means, such as peripheral annular baffles, to direct the flow of gas towards and over the surface of the filter media.
Electrostatic filters are not effective in filtration of liquids as liquids tend to quickly discharge the electrostatic fibers. Liquids can also easily penetrate through the filter's open passageways. Therefore, when used in a breathing filter, an electrostatic filter pack should be shielded from contact with body fluids such as mucosal secretions since these fluids tend to neutralize the electrostatic charge, making filtration less efficient. Further, body fluids could pass through the filter media, exposing other parts of the breathing systems to possible contamination. Hydrophobic (water repellant) membranes are known and have been used to prevent passage of fluids. More particularly, electrostatic breathing filters have been fabricated with a combination of a hydrophobic membrane, electrostatic filter media, scrim (a non-woven polypropylene mesh) and, in some cases, another hydrophobic membrane. This combination has been used to protect the media body from fluids that would otherwise tend to enter it from either direction.
Filter packs of the aforementioned type, i.e., using one or two hydrophobic membranes, filter media, and scrim are fabricated with the outside periphery of the pack heat-sealed in a manner that causes the pack to become one single unit. Such a single unit filter pack is then placed within two halves of a filter housing, and the housing is welded or glued to enclose the filter pack therein. Pinch rings have sometimes been provided near the periphery of the filter housing to hold the single unit filter pack in place and to prevent bypass of fluid around the outside periphery of the filter pack. This arrangement, however, because of plastic and filter pack dimensional tolerance stack up, does not assure that fluid will not flow between the pinch rings and filter pack.
An alternate method of obtaining a fluid seal has been to encapsulate the periphery of the single unit filter pack with a flexible sealant such as silicone, and to then depend upon pinch rings in the housing to compress against the flexible sealant. This approach increases the expense of the manufacturing process and, as in the previously described method of fabrication, fails to assure the presence of a hermetic seal that prevents passage of fluid through the device.
The present invention is intended to provide a method of manufacture which is less expensive than methods suggested heretofore, and which results in the production of a hydrophobic electrostatic breathing filter that eliminates the foregoing problems.
BRIEF SUMMARY OF THE INVENTION
A hydrophobic electrostatic filter constructed in accordance with the present invention comprises a housing having a patient side portion and a machine side portion. Each of these housing portions includes an outer annular edge and an annular pinch ring inward of the outer edge. The filter is fabricated by applying a thin layer of an adhesive to the pinch ring of the patient side housing portion, and then positioning a hydrophobic membrane over that pinch ring to effect a hermetic seal between the hydrophobic membrane and the patient side housing portion utilizing an adhesive interface. Electrostatic filter media and scrim are positioned within the machine side portion of the housing adjacent the pinch ring of said machine the portion, the two housing portions are then engaged in opposing relation to one another to position the pinch rings of the housing portions in at least partially opposed relation to one another, and the outer edges of the engaged housing portions are sealed together by a hot melt adhesive or by ultrasonic welding to form an enclosed filter housing that includes the electrostatic filter media and scrim mechanically fixed in place between the opposed parts of the pinch rings adjacent to the hermetically sealed hydrophobic membrane.
The foregoing method of assembly results in a breathing filter which consists of a hydrophobic membrane that is separate from and independent of the electrostatic media, but which nevertheless protects the electrostatic filter media from exposure to liquids. Particulate migration of electrostatic fibers at the machine side of the housing is prevented by scrim that is located immediately adjacent the electrostatic media element on the side of the media facing the machine side portion of the housing.
The method of assembly simplifies the entire manufacturing process since it is relatively easy to seal the hydrophobic membrane to the pinch ring on the patient side of the housing, and since, further, the electrostatic media does not need to be part of the hermetic seal. The assembly method also provides a high degree of assurance that the hydrophobic membrane will retain its integrity before and after the assembly process.
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Connolly Bove Lodge & Hutz
SIMS Portex Inc.
Srivastava V.
Weiss John G.
LandOfFree
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