the invention may be useful in optimizing blood flow to the heart and brain in states of low blood pressure , head trauma , cardiac arrest and the like . for those suffering from head trauma , venous return to the chest may reduce intracranial pressures as described in co - pending u . s . application ser . no . 10 / 660 , 462 , filed on the same date as the present application , the complete disclosure of which is herein incorporated by reference . for those with low blood pressure , the increased circulation may help to increase their blood pressure . for those in cardiac arrest , blood circulation created by the invention serves to help maintain vital organ functions until resuscitation . in order to provide such circulation , the invention may utilize any device capable of delivering a positive pressure breath followed by the creation of a vacuum to lower the person &# 39 ; s intrathoracic pressure . this may be performed with a mechanical ventilator , a ventilation bag and the like . one embodiment utilizes a ventilator bag that may be compressed and then released to deliver and then extract air from the person . such a bag may include a valve system that permits a positive pressure breath to be delivered when compressing the bag ( referred to as the inspiratory phase ) and then immediately pull a vacuum as the bag is released to cause the pressure within the chest to fall less than atmospheric pressure during the expiratory phase . in some cases , the bag may include a threshold valve as described in u . s . pat . nos . 5 , 551 , 420 ; 5 , 692 , 498 ; 6 , 062 , 219 ; 5 , 730 , 122 ; 6 , 155 , 257 ; 6 , 234 , 916 and 6 , 224 , 562 , and in u . s . patent application ser . no . 10 / 224 , 263 , filed on aug . 19 , 2002 (“ systems and methods filed mar . 28 , 2003 (“ diabetes treatment systems and methods ”, ser . no . 09 / 966 , 945 , filed sep . 28 , 2001 and ser . no . 09 / 967 , 029 , filed sep . 28 , 2001 , the complete disclosures of which are herein incorporated by reference . this valve arrangement may be used to prevent air from entering the person if the pressure within the chest is mechanically manipulated to fall ( such as during the decompression phase of manual cpr or acd cpr ) during the expiratory phase . in some cases , the rescuer may switch the operation from a “ push - pull ” ventilator to one that delivers only positive pressure ventilation , such as is traditional with most ventilator bags ( e . g ., an ambu bag ). one reason for pulling the vacuum during the expiratory phase is to lower the intrathoracic pressure within the chest after each positive pressure ventilation . this negative pressure is transferred to the right heart and lungs , drawing more venous blood back from the extra - thoracic vasculature , and may be used to treat low blood pressure , head trauma and cardiac arrest . the device may be configured to be hand - held , light weight and portable . as the bag decompresses , it “ recharges ” itself so that more air is available during the next squeeze . optionally , a foot peddle may be connected to help develop a greater or more sustained vacuum . it may also include a timing device to provide feedback to the rescuers on how often to ventilate the patient . it may further include a regulator to limit the amount of pressure that builds up with each positive pressure ventilation to prevent stomach insufflation . one example of such a regulator is the smart bag ®, commercially available from mediline . referring now to fig1 , one method for enhancing blood circulation will be described . in so doing , it will be appreciated that such techniques may be used to treat those suffering from head trauma , low blood pressure , and cardiac arrest , among others . at step 10 , the process may begin by interfacing the appropriate equipment to the person . this may include , for example , a pressure and a vacuum source ( such as a bag - valve system having a face mask ), an impedance threshold valve , a positive pressure flow regulator , one or more physiological sensors , a transmitter for transmitting measured signals to a remote receiver , a metronome or other timing device to tell the rescuer when to ventilate and / or create a vacuum , an oxygen source and the like . if the person is in cardiac arrest , the rescuer may perform cpr by performing chest compressions and decompressions as is known in the art . this is illustrated in step 12 . at step 14 , a positive pressure breath is delivered to the person . this is immediately followed by the extraction of respiratory gases to lower the person &# 39 ; s intrathoracic pressure as shown in step 16 . steps 12 - 16 may be repeated as necessary as shown in step 18 . if the person is in cardiac arrest , the steps of delivering a breath and extracting respiratory gases are performed about once for every 5 to 20 chest compressions . the positive pressure breath may be delivered for about 0 . 5 to about 2 . 0 seconds while the vacuum may be produced for about 1 to about 10 seconds . the volume of air delivered may be in the range from about 4 ml / kg to about 20 ml / kg . the negative intrathoracic pressure created may be in the range from about − 1 mmhg to about − 20 mmhg . to create the pressure the generated vacuum may be about one to about three times this amount . for those suffering from low blood pressure or head trauma , steps 14 and 16 may be continuously performed as long as treatment is needed . the positive pressure breath may last about 0 . 5 to about 3 seconds and have a volume of about 4 ml / kg to about 20 ml / kg . the vacuum may be produced immediately after the positive pressure breath and last about 1 second to a bout 6 seconds . the resulting negative intrathoracic pressure may be about − 1 mm hg to about − 20 mm hg and may be producing using a vacuum that is one to about three times this amount . particular techniques for supplying the breath and extracting gases are described hereinafter with respect to fig5 a - 5c . also , it will be appreciated that the vacuum may be producing using a flow of gases or with no flow , and the time and / or amount of the vacuum may be varied . as shown in step 20 , an impedance threshold valve or other device may be used to prevent or impede respiratory gases from entering the patient &# 39 ; s lungs . this may be done , for example , when performing cpr . during decompression after the chest , air is typically drawn into the person &# 39 ; s airway . using an impedance valve , air is prevented from rushing in until a certain negative intrathoracic pressure is reached . at this time , the valve opens to permit gases to flow to the lungs . such techniques are described in the references incorporated herein . for cpr applications , the valve may be set to open when the negative intrathoracic pressure exceeds about − 4 cmh 2 o to about − 15 cmh 2 o . such an impedance valve may also be used in non - cpr applications as well when the person inspires . in such cases , the valve may be set to open at about − 3 cm h 2 o to about − 12 cmh 2 o . in step 22 , the volume , rate and or pressure of the positive pressure breath may be regulated . in this way , the patient may be protected against insufflation . in step 24 , supplemental oxygen may be supplied to the patient . this may be supplied based on measured parameter as described below . also , the oxygen may be delivered to the bag - valve system . in step 26 , one or more physiological parameters may optionally be monitored . the treatments described herein may be varied based on the measured parameters . examples of such parameters include end tidal co 2 , oxygen saturation , blood pressure , cardiac output and the like . other parameters as well as equipment and sensors that maybe be used are described in copending u . s . application ser . no . 10 / 660 , 462 , filed on the same date as the present application ( and incorporated therein by reference ) as well as in the other references incorporated herein . these may be coupled to a controller or other computer to record the measurements , display the measured parameters , recommend or control a specific treatment and the like . as shown in step 28 , information on the measured parameter may also be transmitted to a remote receiver . this may be over a variety of communication paths or networks , such as wireless networks , cell phones , local area networks , the internet and the like . this information may be used to evaluate the treatment , monitor the quality of treatment , and command a treatment or the like . for example , the information may be transmitted to a hospital or health care facility where a physician may recommend how to apply the positive pressure breaths or extract the respiratory gases . referring now to fig2 , one embodiment of a bag - valve resuscitator 30 will be described . resuscitator 30 may be used in association with any of the methods described herein . resuscitator 30 comprises a compressible bag 32 that is divided into a supply chamber 34 and an exit chamber 36 . bag 32 may be constructed of an elastomeric material that permits bag 32 to self - expand after it has been compressed . optionally , an elastomeric material may be placed in one or both of the chambers to facilitate expansion of bag 32 after it has been compressed . bag 32 also includes an entrance port 38 and a one - way inflow valve 40 . when bag 32 is compressed , air , oxygen or other respiratory gases in supply chamber 34 are forced through inflow valve 40 and into a conduit 42 where they may be supplied to a person &# 39 ; s airway . optionally , an interface may be coupled to conduit 42 to couple resuscitator 30 to the patient . such interfaces may include facial masks , endotracheal tubes , and the like . when bag 32 is released , it expands to its normal position . in so doing , inflow valve 40 closes allowing air or other respiratory gases to flow into chamber 34 . optionally , a flow restrictive device may be used to regulate the flow of air into conduit 42 . this may provide a fixed resistance or a variable resistance . bag 32 also includes an exit port 44 and a one way outflow valve 46 . when bag 32 is compressed , valve 46 closes and gases in chamber 36 may exit through port 44 . as bag 32 expands , valve 46 opens to pull respiratory gases from the patient &# 39 ; s airway . hence , a positive pressure breath may be delivered when bag 32 is compressed and gases may be extracted when bag 32 is released . in so doing , the person &# 39 ; s intrathoracic pressure is lowered to pull venous blood back into the chest . optionally , one or more sensors 48 may be incorporated into or coupled to resuscitator 30 . examples of sensors that may be used include any of those described or incorporated herein . as another option , a timer 50 may be coupled to or associated with bag 32 . timer 50 may be a flashing light , a speaker or the like to indicate when bag 32 should be compressed . this information may be pre - programmed or varied based upon measurements from sensor 48 . as shown in fig3 , conduit 42 may be modified to include a positive end expiratory pressure ( peep ) valve 52 for non - breathing patients . this is located in a non - breather port 54 . peep valve 52 may be used when the resuscitator bag is switched from one device capable of “ pushing and pulling ” to one that is locked in the “ traditional ” positive pressure ventilator mode only . however , in some cases , peep valve 52 may be used intermittently , such as every other or every third ventilation cycle . resuscitator 30 may also include a switch or a closure valve 56 that may move to a position that blocks outflow valve 46 . in so doing , the “ pull ” feature is turned off so that respiratory gases are not actively extracted during the expiratory phase . in another position , valve 56 may be moved to a position closing non - breather port 54 . this option allows for standard positive pressure ventilation and for push / pull ventilation . as another option , an impedance threshold valve may be positioned over conduit 42 or anywhere between the bag and the patient . this valve is particularly useful when performing cpr . when bag 32 is compressed , gases flow through the threshold valve and to the patient to provide proper ventilation . when performing cpr respiratory gases exiting the patient during compression of the chest pass through the impedance valve and out valve 46 . during decompression of the chest , gases are prevented from entering the patient &# 39 ; s lungs because of the impedance valve . this valve opens when a certain negative intrathoracic pressure is achieved when opened gases may enter conduit 42 through valve 40 . such an impedance valve is described in the references incorporated herein . fig4 illustrates another embodiment of a bag - valve resuscitator 60 that comprises a compressible bag 62 that is constructed of an elastomeric material so that it will expand to its original shape following a compression . bag 62 includes a main ventilation chamber 64 that is filled with air or other respiratory gases . when bag 62 is compressed , air in chamber 643 is directed through a ventilation port 66 , through a fish mouth valve 68 and into a ventilation tube 70 where it is supplied to the patient through a patient support 72 . ventilation chamber 64 is refilled as bag 62 is released and returns to its uncompressed shape . more specifically , as bag 62 decompresses , a negative pressure within main ventilation chamber 64 is produced . this opens a one way valve 76 allowing air to flow through a venturi tube 78 , through a fish mouth valve 80 , through ventilation port 66 and into chamber 64 . following ventilation , passive expiratory gases from the patient may flow through patient port 72 , into an expiratory chamber 82 and out a one way valve 84 . the generation of the negative intrathoracic pressure occurs during the passive recoil or decompression of bag 62 . more specifically , air flowing through venturi tube 78 creates a venturi effect in tube 86 . this creates a negative pressure within a negative chamber 88 . in turn , this cases a secondary chamber 90 ( which is collapsed ) to pen , thereby including air flow through a fish mouth valve 92 , through a supply tube 94 and into secondary chamber 90 . secondary chamber 90 may hold a volume of about 100 milliliters to about 150 milliliters when filled . when bag 62 is again compressed , gas stored in secondary chamber 90 is directed through an exhaust tube 96 and expelled through a fish mouth valve 98 . hence , resuscitator 60 may be used in any of the procedures described herein . also , resuscitator 60 may include any of the other features described in connection with other embodiment described herein , such as flow regulators , threshold valve , sensors , peep valves , switches and the like . the manner in which positive pressure breaths and the vacuum are created may vary depending upon a particular application . these may be applied in a variety of waveforms having different durations and slopes . examples include using a square wave , biphasic ( where a vacuum is created followed by positive pressure , decay ( where a vacuum is created and then permitted to decay ), and the like . three specific examples of how this may occur are illustrated in fig5 a - 5c , although others are possible . for convenience of discussion , the time during which the positive pressure breath occurs may be defined in terms of the inspiratory phase , and the time during which the intrathoracic pressure is lowered may be defined in terms of the expiratory phase . as shown in fig5 a , respiratory gases are quickly supplied up to a pressure of about 22 mmhg . this is immediately reversed to a negative pressure of about − 10 mmhg . this pressure is kept relatively constant until the end of the expiratory phase where the cycle is repeated . in some cases , the cycle may go from a push - pull every breath to a push , then push - pull every other breath or every third breath , i . e . as a 2 : 1 or 3 : 1 push : pull option . in fig5 b , the positive pressure is more slowly applied . when reaching a pressure of about 10 to about 15 mmhg , the pressure is rapidly reversed to a negative pressure of about − 20 mmhg . the negative pressure gradually declines to about 0 mmhg at the end of the expiratory phase . the cycle is then repeated . hence , in the cycle of fig5 b , the positive pressure is reduced compared to the cycle in fig5 a , and the negative pressure is initially lower , but allowed to gradually increase . the technique is designed to help reduce a possible airway collapse . in fig5 c , the positive pressure is brought up to about 20 mmhg and then immediately brought down to about 0 mmhg . the negative pressure is then gradually increased to about − 20 mmhg toward the end of the expiratory phase . this cycle is designed to help reduce a possible airway collapse . the invention has now been described in detail for purposes of clarity and understanding . however , it will be appreciated that certain changes and modifications may be practiced within the scope of the appended claims .
a device for manipulating intrathoracic pressures comprises a compressible bag structure , and an interface member coupled to the bag structure . a one way forward valve is coupled to the bag structure to permit respiratory gas to flow to the patient when the bag structure is compressed . a one way exit valve is employed to allow respiratory gases to be pulled from the person &# 39 ; s airway upon decompression of the bag structure to produce a negative intrathoracic pressure .