Positive pressure filter system for inflatable blanket heaters

An inflatable blanket heater draws room air into the unit through a filtered intake by an electrically-powered blower. The air is compressed by the blower and warmed by an electric heater in the unit. The warmed air is forced through an outlet filter that removes air particles down to 0.2-micron. The filtered warmed air is delivered to a convective (inflatable) heating blanket by an air delivery hose.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates generally to improvements in air filters and, 
more particularly, pertains to a new and improved air filtration system 
used in heater units for supplying air to inflatable blankets which are 
used to maintain a certain body temperature for hospital patients, for 
example. 
2. Description of Related Art 
In the field of inflatable blanket heaters, it has been a practice to 
employ an electrically-powered blower and an electric heater to heat the 
air being supplied to the inflatable blanket which is, in turn, 
distributing the warmed air over the body of a patient. The temperature of 
the heated air can be controlled through the electric heater. 
Traditionally such units draw in ambient air which is heated and then 
distributed to the surface areas of the patient. This ambient air is 
typically filtered at the intake. Although filters are utilized in these 
units for the ambient air drawn from a hospital environment, these filters 
have been unsatisfactory, particularly in situations where the air is 
being used to warm the body of a patient that is highly susceptible to 
infection through the skin, such as a burn patient, for example, or by 
inadvertent airflow over a surgical field. Hospitals are known for having 
environments that contain many impurities. The impurities of concern are 
generated outside of the inflatable blanket heater, as well as, perhaps, 
by the blower and heater units themselves. 
OBJECTS AND SUMMARY OF THE INVENTION 
An object of the present invention is the provision of an inflatable 
blanket heater that is highly efficient. 
Another object is to provide a filter system for an inflatable blanket 
heater that filters out particles as small as 0.2-micron. 
These objects and the general purpose of this invention are accomplished by 
utilizing a filter at an outlet of the inflatable blanket heater which 
filter is constructed to provide highly efficient particulate removal. The 
filter has a body with an input and an output aperture. A filter media 
that filters out up to 0.2-micron particles is sealed by its perimeter 
edges to the interior of the filter. A lid with an outlet port is sealed 
to the output aperture of the filter body. Filtering air at the output 
with the positive outlet pressure prevents drawing particles through 
inescapable leaks in the air delivery system, assuring delivery of clean 
air.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The following description is provided to enable any person skilled in the 
art to make and use the invention and sets forth the best modes 
contemplated by the inventors of carrying out their invention. Various 
modifications, however, will remain readily apparent to those skilled in 
the art, since the generic principles of the present invention have been 
defined herein specifically to provide assurance of delivery of filtered 
air of known particle size limit to site of patient application. 
FIG. 1, which illustrates the entire inflatable blanket heater unit within 
which the filter system of the present invention is located in its 
preferred embodiment, shows the inflatable blanket heater as comprising a 
cabinet 11 mounted on wheels 21 with a curved handle 13 attached to the 
cabinet 11. The front panel 17 of cabinet 11 contains an air intake 
opening 19 which may contain an intake filter 60 therein. The heater unit, 
in addition, has a control panel 15 for setting the air temperature 
desired. A hose support bracket 31 is mounted on a shaft 32 which slides 
within a sleeve block 38. The block 38 has a hand-operable bolt 34 
threaded therein to hold fast rod 32 at selected positions. 
FIG. 2 illustrates the back side of the inflatable blanket heater of FIG. 
1, showing the power cord 23 going into cabinet 11 with storage brackets 
24 mounted thereon. The power cord 23 is shown wound around the storage 
brackets 24. 
An outlet filter lid 25 is mounted to the cabinet 11 by at least four 
mounting screws 27. Lid 25 has an outlet port 33 to which is attached a 
warm air conducting hose 29. Hose support bracket 31 aids in positioning 
hose 29. At the other end of hose 29, an attachment mechanism 36 is 
utilized for attaching the hose to any number of patient-warming blankets, 
such as manufactured by the inventors herein or the BAIR HUGGER 
manufactured by Augustine Medical, the WARM TOUCH manufactured by 
Mallinckrodt Medical, and the THERMOCARE manufactured by Gamar, for 
example. 
FIG. 3 illustrates, in an exploded manner and in cutaway, various features 
of the preferred embodiment of the present invention in more detail. The 
cabinet 11 is shown in side view with a cutaway illustrating the 
electrically-powered blower 51 and a heating column 53. The heating column 
53 may be a plenum chamber containing an electric heater used to heat the 
air within. Plenum chamber 53 has an outlet port (not shown) which mates 
with a lower inlet port extension 42 of a filter bin 37. Filter bin 37, in 
assembly, resides completely within cabinet 11. Overlaying filter bin 37 
is the cabinet top 35 to which is fastened the handlebar 13 by way of 
bolts 14. 
The cabinet top 35 has an aperture therein which allows the outlet filter 
body 26 with the lid 25 attached thereto to seal to the perimeter of the 
upper rim 44 of bin 37, the filter body 26 resting within bin 37 in 
assembly. Outlet filter body 26 has an open bottom 46. Lid 25 has an air 
outlet port 33 to which a mating couple 30 from an air transport hose 29 
attaches. 
Referring now to FIG. 4, which illustrates an exploded view of the outlet 
filter assembly of FIG. 3 with the lid 25 on top and the outlet filter 
body 26 on the bottom, the entire outlet filter assembly is fastened to 
the cabinet top 35 (FIG. 3) and sealed against cabinet top 35 by a gasket 
39 being compressed between the underside of lid 25 and cabinet top 35 by 
the filter mounting screws 27. 
Filter media 45 is sandwiched between an apertured upper potting plate 47 
and a lower potting plate 43, which is cemented to and forms a part of 
filter media 45. The filter media assembly is then placed into the outlet 
filter body 26, which has an open bottom 46 and an open top 48. The filter 
body 26 has a stepped configuration, as shown in FIG. 4. The perimeter 
edge 50 of the filter media 45, with the potting plates 47 and 43, is 
sealed to the internal walls of the outlet filter body, preferably by a 
urethane potting compound. The middle of the filter is left clear to pass 
airflow entering at the open bottom 46 of the filter body, through the 
filter media 45 and out the open top 45 of the filter body to the lid 25, 
and out an exit port 33. The lid 25 caps the outlet filter body 26 and is 
sealed to the lip 41 of filter body 26, preferably by an ABS cement. 
In operation, the inflatable blanket heater takes in ambient air through 
the air intake opening 19 in the cabinet 11 and inlet filter 60 as a 
result of blower 51 drawing in ambient air and compressing it in plenum 
chamber 53 containing electrical heater elements which warm the air and 
pass it to the intake extension 42 of filter bin 37. The top 44 of outlet 
filter bin 37 is sealed by cabinet top 35 and filter body lid 25, thus 
forcing the air through the bottom opening 46 of filter body 26. The 
warmed air passes through filter media 45 located within filter body 26 to 
output port 33 in the lid 25. 
During transport, the outlet port 33 in lid 25 is capped temporarily by cap 
49. 
The filter media 45 is preferably a material of the kind that has the 
capability of removing from the warm air passing through it, particulate 
matter that is as small as 0.2-micron. Placement of the 0.2-micron filter 
at the outlet side of the heater, rather than at the inlet side before the 
blower, assures that air passing through the filter is under positive 
pressure relative to ambient. Any minute leak following or before the 
filter will not serve as a path for particulate entry to the airstream. In 
contrast, filtering at the inlet requires a system which has no leaks in 
the airflow path up to the blower, including flow through the filter and 
cabinet. The resulting airflow delivered by Applicants' embodiment is 
contaminate-free and a major improvement over the inflatable blanket 
heaters of the prior art. 
It should be understood, of course, that the foregoing disclosure relates 
only to a preferred embodiment of the invention, and that modifications 
may be made therein without departing from the spirit and scope of the 
invention as set forth in the appended claims.