as shown in fig1 an anesthetic filter arrangement has a filter housing 2 in which open - ended conduit sections 4 , 6 are formed for leading a gas to and from an interior gas - flow portion 8 of the housing 2 . contained within the interior portion 8 , and arranged for gas communication with gas therein , is a filter element 10 formed of a suitable sorption material for anesthetic agent . examples of such material are zeolites of crystalline aluminum silicates that may be pellets or supported on a carrier and an activated carbon filter such as formed from carbon - impregnated material , carbon fiber cloth , or granulated or microporous carbon material . other known adsorptive and / or absorptive microporous material also can be used . a peltier effect element 12 is provided with a warming surface 12 a in intimate thermal contact with a first gas flow circuit 14 , 16 using , in the present embodiment , a first known heat exchange unit 18 a , such as may simply be formed by a gas flow conduit having a number of internal ridges , fins or channels to increase the surface area over which heat may be exchanged between gas from the first flow circuit 14 , 16 and the warming surface 12 a . a cooling surface 12 b , opposite the warming surface 12 a of the peltier element 12 is arranged in intimate thermal contact with a second gas flow circuit 22 , 24 , here using a second known heat exchange unit 18 b which together with the first heat exchange unit 18 a may form a single known heat exchanger . the two sections 14 , 16 of the first gas flow circuit are arranged in gas flow communication with the gas conduit 4 of the housing 2 , each on an opposite flow side of a first one - way valve 20 arranged to permit a through flow of gas in a direction from the filter element 10 only . the two sections 22 , 24 of the second gas flow circuit are arranged in gas flow communication with the gas conduit 6 of the housing 2 , each on an opposite flow side of a second one - way valve 26 arranged to permit a through flow of gas in a direction from the filter element 10 only . as is illustrated in fig1 the one - way valves 20 , 26 may be provided integral with corresponding connector bodies 28 , 30 which are respectively releasably connected to the conduit sections 4 , 6 of the housing 2 . these connector bodies 28 , 30 are intended for releasable coupling with a gas flow circuit of an anesthetic ventilator system in a manner such that , in use , inspiration gas from the ventilator will flow into the housing 2 through the connector body 28 and expiration gas from a patient will flow into the housing 2 through the connector body 30 . this enables the filter element 10 to be easily introduced into and removed from the gas flow circuit . gas ports 32 , 34 are provided at each side of the first one - way valve 20 to provide gas communication between the interior of the connector body 28 and the two conduits 14 , 16 of the first gas flow circuit . similarly , gas ports 36 , 38 are provided at each side of the second one - way valve 26 to provide gas communication between the interior of the body 30 and the two conduits 22 , 24 of the second gas flow circuit . when in use , the exemplary configuration of the anesthetic filter arrangement of fig1 allows gas from a patient ( expiration gas ) will pass through the filter element 10 in a direction from the conduit 6 to the conduit 4 . gas to be supplied to a patient ( inspiration gas ) is allowed to pass through the filter element 10 in an opposite direction , that is , from the conduit 4 to the conduit 6 . the intended directions of gas flow through the filter arrangement are shown by the arrows in fig1 . in use , the operation and location of the second one - way valve 26 causes expiration gas to flow through the conduit 22 of the second gas flow circuit and to the second heat exchange unit 18 b where it becomes cooled by the action of the appropriately energized peltier device 12 using , in a known manner , a power supply unit ( not shown ). the cooled gas passes from the second heat exchange unit 18 b , through the conduit 24 and into the filter housing 2 through the conduit section 6 . the cooled gas then passes through the filter element 10 , which retains anesthetic agent present in the expiration gas , and out of the filter housing 2 through the conduit 4 and the first one - way valve 20 . the amount of anesthetic agent retained by the filter element 10 is enhanced because of the cooling effect of the gas passing through it . as the expiration gas is cooled , water vapor that is normally present in expiration gas will condense . it may be useful to provide a known water trap ( not shown ) in communication with the cooled expiration gas at a location before it contacts the filter element 10 to collect this condensate . more usefully such a water trap may be provided in communication also with inspiration gas at a location after it contacts the filter element 10 to moisten , in a known manner , the inspiration gas before delivery to a patient . the operation and location of the first one - way valve 20 causes inspiration gas to pass through the conduit 14 of the first gas flow circuit and to the first heat exchange unit 18 a where it becomes heated by the action of the appropriately energized peltier device 12 . the warmed gas passes from the first heat exchange unit 18 a , through the conduit 16 the filter housing 2 through the conduit section 4 . the warmed gas then passes through the filter element 10 , which releases previously retained anesthetic agent into the inspiration gas , and out of the filter housing 2 through the conduit 6 and the second one - way valve 26 . the release of the anesthetic agent by the element 10 is thus enhanced because of the warming effect of the inspiration gas passing through it . typically , a small amount of carbon dioxide that is present in the expiration gas will be retained by the filter element 10 and will be released into the inspiration gas together with the anesthetic agent . this might be expected to be the detriment of the anesthetic ventilation therapy being provided . it has been discovered by the present inventors , however , that the amount of carbon dioxide which , in use , is re - supplied toward a patient from the filter arrangement according to the present invention is unexpectedly reduced in comparison to the amount re - supplied from a known filter arrangement . as described above , the peltier element 12 and the heat exchange units 18 a , 18 b together form a thermal regulating device for varying the temperature of the filter element 10 by varying the temperature of the gases incident on the filter element 10 . the temperature of the incident gases can be controlled by varying the electric current flowing through the peltier element 12 which , in a known manner , varies the degree of cooling / heating produced by the element 12 . it will be appreciated that in the exemplary configuration of fig1 the peltier device 12 may be appropriately energized so that the warming side becomes 12 a and the cooling side becomes 12 b . in the use described above expiration gas will now become warmed to thereby diminish the retention by the filter element 10 of gaseous anesthetic present in the expiration gas . the inspiration gas will become cooled to thereby diminish the release of previously retained anesthetic in to the inspiration gas . this may be useful , for example , when trying to wake up a patient . moreover , the peltier device 12 and heat exchange units 18 a , 18 b may be substituted with other active thermal regulation devices , such as refrigerant compression , capable of providing a cooling and optionally a heating effect at the filter element 10 . also a passive heat exchanger may substitute for the peltier device 12 and heat exchange units 18 a , 18 b . in such a passive heat exchanger the heat of the relatively warmer expiration gas is used to warm inspiration gas and itself becomes cooled in the process . an example of a peltier effect thermal regulating device suitable for use in , for example , the anesthetic filter arrangement of fig1 is shown in fig2 a and 2 b . considering now fig2 a , an internal portion of the device is shown in an exploded form to enable components to be more clearly seen . multiple , here five , peltier effect elements 12 are arranged in a stack so that , when the elements 12 are suitably energized , warming 12 a and cooling 12 b faces of adjacent elements face one another . between each peltier element 12 and in intimate thermal contact therewith is a gas flow conduit 40 , 42 . each gas flow conduit is oriented to provide a direction of gas through - flow ( indicated by arrows 44 , 46 in the fig2 ) selected dependent on which of the faces 12 a or 12 b of the adjacent peltier elements 12 it is in intimate thermal contact with . as illustrated in the present example , all of those gas flow conduits 40 that are arranged in thermal contact with a cooling side 12 b of peltier elements 12 are oriented to provide for through flow of gas in a single flow direction 44 that is orthogonal to a single flow direction 46 for gas flowing through those conduits 42 that are arranged in thermal contact with a warming side 12 a of a peltier element 12 . as is also illustrated in fig2 a , each conduit 40 , 42 is formed , as is preferable , with an increased internal surface area that in the present embodiment is realized by the inner surfaces of channels 48 . the increased surface area increases the efficiency with which thermal energy can communicate between gas within the conduit 40 , 42 and the associated face 12 b , 12 a of a peltier element 12 . as shown in fig2 b , a housing 50 is provided to contain the stacked arrangement of fig2 a . an orthogonal arrangement of externally accessible gas flow conduits 52 a , 52 b , 54 a , 54 b is provided in opposing walls of the housing 50 to define flow paths for gas between external and internal the housing 50 that communicate with respective flow paths 44 , 46 through the associated conduits 40 , 42 of the stack of fig2 a . thus , referring to fig1 it is intended that the flow conduits 22 , 24 of the second gas flow circuit will be connected with the gas flow conduits 52 a , 52 b of the housing 50 and that the flow conduits 14 , 16 of the first gas flow circuit will be connected with the gas flow conduits 54 a , 54 b of the housing 50 . usefully , although not essentially , pressure sensors 56 a , 56 b may be located within the conduits 54 a , 54 b of the housing 50 to provide pressure readings to a differential pressure ( δp ) meter 58 by which gas flow ( here inspiration gas flow ) through the housing 48 can be calculated in a manner well known in the art . similar pressure sensors 60 a , 60 b may be located within the conduits 52 a , 52 b and connected to a differential pressure meter ( δp ) 62 in order to gain a measure of gas flow ( here expiration gas flow ) through the housing 50 . although modifications and changes may be suggested by those skilled in the art , it is the intention of the inventors to embody within the patent warranted hereon all changes and modifications as reasonably and properly come within the scope of their contribution to the art .
an anesthetic filter arrangement for the reflection of unused anesthetic agent in expiration gas back toward a patient has a filter housing having an interior portion arranged to provide an internal gas flow path for an inspiration gas and for an expiration gas passing alternately and in opposite directions through the housing and a filter element disposed in gas communication with the interior portion for adsorption of anesthetic agent from the expiration gas and subsequent desorption of the anesthetic agent into the inspiration gas . the arrangement further . has a thermal regulator operable to reduce thermal energy at the filter element by cooling one or both incoming gas and the filter element , and thereby vary one or both the adsorption and the desorption of the anesthetic agent .