Abstract:
A gas-driven chest compression apparatus for cardiopulmonary resuscitation (CPR) comprises a flexible pneumatic actuator, capable of axial contraction when fed with a pressurized driving gas, and means for controlling the contraction thereof. Also disclosed are methods of providing chest compressions to a patient by means of a CPR apparatus comprising actuator(s) of this kind, and a corresponding use of the actuator.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     The present application is a 35 U.S.C. §371 National Phase conversion of PCT/SE2008/000063, filed Jan. 25, 2008, which claims benefit of Swedish Application No. 0700304-9, filed Feb. 8, 2007, the disclosure of which is incorporated herein by reference. The PCT International Application was published in the English language. 
     FIELD OF THE INVENTION 
     The present invention relates to a gas-driven chest compression apparatus for cardiopulmonary resuscitation. 
     BACKGROUND OF THE INVENTION 
     Sudden cardiac arrest is commonly treated mechanically and/or by electrical defibrillation. Mechanical treatment may be given manually or by a chest compression apparatus. A number of chest compression apparatus are known in the art, such as the pneumatically driven LUCAS™ mechanical chest compression system (“Lucas™ system”; an apparatus for compression and physiological in CardioPulmonary Resuscitation, CPR, manufactured by Jolife AB, Lund, Sweden). Specifically the Lucas™ system comprises a support structure and a compression unit. The support structure includes a back plate for positioning under the patient&#39;s back posterior to the patient&#39;s heart and a front part for positioning around the patient&#39;s chest anterior to the heart. The front part has two legs, each having a first end pivotally connected to a hinge of the front part and a second end removably attachable to the back plate. The front part is devised to centrally receive the compression unit, which is arranged to repeatedly compress the patient&#39;s chest. The compression unit comprises a pneumatic means arranged to drive and control compression, an adjustable suspension means to which a compression pad is attached, and a means for controlling the position of the pad in respect of the patient&#39;s chest. The use of a pneumatic means as the driving force relies on a reciprocating piston providing compressions on the chest by the pad, driven by pressurized gas. The system utilizes pressurized gas for driving the piston both ways, i.e. in the direction of the patient&#39;s chest (compression phase, gas being supplied to a compression chamber) and then in the opposite direction (gas being supplied to a decompression chamber), whereby the sternal portion of the chest is brought back to its original position (decompression phase). The consumption of pressurized gas can be substantial and is a limiting feature on the use of the apparatus in places where supply of pressurized driving gas is limited. The consecutive supply of driving gas to the two chambers of the known apparatus requires a complex and thus expensive valve system and a correspondingly complex control. 
     OBJECTS OF THE INVENTION 
     It is an object of the present invention to provide an apparatus of the aforementioned kind, which only consumes pressurized gas when the chest compression pad imposes a force on the patient&#39;s sternum. 
     It is another object of the invention to provide an apparatus of the aforementioned kind, in which the control of driving gas is simplified. 
     Further objects of the invention will be evident from the following summary of the invention, the description of preferred embodiments thereof illustrated in a drawing, and the appended claims. 
     SUMMARY OF THE INVENTION 
     According to the present invention is disclosed the use of an axially contractible pneumatic actuator as a driving force generator for an apparatus for cardiopulmonary resuscitation by administration of chest compressions to a patient in need thereof. In this application “actuator” refers to an axially contractible flexible pneumatic actuator. 
     An axially contractible flexible pneumatic actuator suitable for the use in the present invention is disclosed in EP 0 146 261. The actuator comprises a hose body extending between two spaced head pieces. The hose body is flexible whereas the end pieces are solid and generally of a metal. When a fluid under pressure, such as a driving gas, is adduced to its lumen the hose body expands radially. Thereby the distance between the head pieces is shortened. This shortening or contraction can be used as a pulling force. The contraction force of the known actuator is proportional (however not linearly) to the pressure of the driving gas. An actuator of this kind can be used, for instance, to lift or pull weights. An improved pneumatic actuator of this kind is disclosed in U.S. Pat. No. 6,349,746, which is incorporated herein by reference. 
     According to the present invention is also disclosed a CPR apparatus comprising one or more axially contractible flexible pneumatic actuators driven by pressurized gas, in particular pressurized breathing gas. It is preferred for the CPR apparatus to comprise a back plate on which a patient in need of CPR is resting with his back, one or both ends of the one or more actuators being fixed at the back plate. The back plate is preferably oblong in a transverse direction, in particular about rectangular. Fixation of the one or more actuators at the back plate is preferably at the short sides of the plate, which is of a transverse length so at to extend at both sides of the patient. It is also preferred for the CPR apparatus to comprise a chest compression pad on which the one or more actuators act for compression of the patient&#39;s chest. It is also preferred to arrange a base plate between the compression pad and the actuator. The back plate and the compression pad may be integral or separate. 
     According to a first preferred aspect of the invention the CPR apparatus comprises an actuator fastened at the back plate at its both ends, at least one end being releasably fastened. In such case it is preferred for the actuator to abut to the base plate or to an element in abutment with the base plate. Particular preferred is the disposition of the portion of the actuator abutting the base plate in a slot or groove in the upper face of the base plate. It is preferred for the portions of the base plate or of an element disposed between the base plate and the actuator that are in contact with the actuator to have a smooth surface and a low coefficient of friction, such as a coefficient of friction of a polyfluorinated hydrocarbon polymer, in particular Teflon®. The element disposed between the base plate and the actuator can, for instance, be a coat of such polyfluorinated hydrocarbon. 
     According to a second preferred aspect of the invention the CPR apparatus comprises two actuators fixed to opposite sides of the back plate with the first ends and to the base plate with their second ends. In this context “fixed to” comprises fixation via intermediate connection means, such as hooks, rods with eyes, straps, belts, etc. At least one of the fixations should be releaseable to facilitate the mounting of the apparatus to the patient. 
     According to a third preferred aspect the one or more actuators of the CPR apparatus of the invention are enclosed by optionally resiliently flexible shielding tubes. It is preferred for the one or more actuators to be arranged displaceable in the shielding tubes; in such case it is also preferred for the portion(s) of the inner face of the shielding tubes in contact with an actuator to have a low coefficient of friction, such as one of a polyfluorinated hydrocarbon polymer, in particular Teflon®. It is also preferred for such inner face to have a coat of a polyfluorinated hydrocarbon or other low-friction polymer. 
     A preferred polymer for any of base plate, back plate, and compression pad is polyamide reinforced with carbon, glass or other fibre. 
     According to a fourth preferred aspect of the invention an actuator is provided at its one end with a quick coupling of known kind by which it can be releasably fixed to the driving gas line or a gas conduit in the base plate or the back plate. If fixed to a gas conduit in the base plate or the back plate, the quick coupling must be one that withstands the pulling strain exerted on it during contraction of the actuator. Quick couplings suitable for use in the invention are, for instance, low pressure monocouplings series LS manufactured by Carl Kurt Walther GmbH &amp; Co. KG (Haan, Germany). 
     According to a fifth preferred aspect of the apparatus of the invention comprises a releaseable means for adjustment of the position of the base plate/compression pad assembly in respect of the patient, so as to fix the compression pad in a position in which it abuts the breast of the patient while not compressing it and while the one or more unloaded actuator are kept in a straightened state. The adjustment means is preferably selected from means for adjusting the position of the compression pad in respect of the base plate or/and the position of the base plate in respect of the back plate. 
     According to a sixth preferred aspect of the invention an actuator is provided with a resiliently compressible means such as a steel coil that accelerates the return from an inflated state to a non-inflated state. It is preferred for the resiliently compressible means to partially or fully enclose the actuator. 
     According to a seventh preferred aspect of the invention the CPR apparatus comprises a means for control of driving gas of constant pressure supplied by a driving gas source such as a gas cylinder provided with a pressure reduction valve, the means comprising a valve for adducing and venting drive gas to/from the actuator controlled by a timing module optionally coupled to pressure sensor, and optionally comprising a mechanically operated safety valve. 
     According to a further preferred aspect of the invention the gas for driving the actuator is air. Air vented from the actuator can be adduced to the lungs of the patient by a breathing mask or by intubation. 
     According to the present invention is also disclosed the use of an axially contractible flexible pneumatic actuator in a CPR apparatus for providing chest compression to a patient in need thereof. The CPR apparatus may additionally comprise a means for providing electric stimulation to the heart. 
     The invention will now be explained in more detail by reference to preferred embodiments illustrated in a rough drawing. 
    
    
     
       DESCRIPTION OF THE FIGURES 
         FIG. 1   a  is a sectional view (in part; section A-A in  FIG. 1   c ) of a first embodiment of the apparatus of the invention, with the actuator in a non-inflated state (passive); 
         FIG. 1   b  is the apparatus of  FIG. 1   a  and in the same view, with the actuator in an inflated (active) state; 
         FIG. 1   c  is a top view of an actuator/compression plate/compression pad assembly of the embodiment of  FIGS. 1   a  and  1   b;    
         FIG. 1   d  is a enlarged sectional view B-B ( FIG. 1   b ) of the assembly of  FIG. 1   c;    
         FIG. 2   a  is a sectional view (in part, in a section corresponding to that of  FIG. 1   a ) of a second embodiment of the apparatus of the invention, with the actuator in a non-inflated (passive) state; 
         FIG. 2   b  is the apparatus of  FIG. 2   a  and in the same view, with the actuator in an inflated (active) state; 
         FIG. 2   c  is sectional enlarged view C-C ( FIG. 2   b ) of an actuator/compression plate/compression pad assembly of the embodiment of  FIGS. 2   a  and  2   b  including a shielding tube; 
         FIG. 3   a  is a sectional view (in part, in a section corresponding to that of  FIG. 1   a ) of a third embodiment of the apparatus of the invention, with the actuator in a non-inflated (passive) state; 
         FIG. 3   b  is the apparatus of  FIG. 3   a  and in the same view, with the actuator in an inflated (active) state; 
         FIG. 4  is a sectional view (in part, in a section corresponding to that of  FIG. 1   b ) of a fourth embodiment of the apparatus of the invention, with the actuator in an inflated (active) state; 
         FIG. 5  is an partial view of a fifth embodiment of the apparatus of the invention, in a section corresponding to that of  FIG. 1   a , with the actuator in an inflated (active) state; 
         FIG. 6   a  is a sectional view (in part, in a section corresponding to that of  FIG. 1   b ) of a fifth embodiment of the apparatus of the invention, with the actuator in a non-inflated (inactive) state; 
         FIG. 6   b  is the apparatus of  FIG. 6   a  and in the same view, with the actuator in an inflated (active) state; 
         FIG. 7  is a sectional view (in part, in a section corresponding to that of  FIG. 1   b ) of a sixth embodiment of the apparatus of the invention, with the actuator in an inflated (active) state; 
         FIG. 7   a  is a top view of the compression plate of the embodiment of  FIG. 7 ; 
         FIG. 7   b  is a short side view of the compression plate of  FIG. 7   a;    
         FIG. 8  is a variation of the compression plate of  FIG. 7   a , in a top view; 
         FIG. 8   a  is a sectional view D-D ( FIG. 8 ) of the compression plate of  FIG. 8 ; 
         FIG. 8   b  is a partial view of the compression plate of  FIG. 8  in a state mounted on the chest of a patient, the view corresponding to that of  FIG. 1   a;    
         FIG. 9  is a variation of the compression plate of  FIG. 8 , in a sectional view corresponding to that of  FIG. 8   a;    
         FIG. 10  is a pneumatic control scheme for an apparatus of the invention. 
     
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     The chest compression apparatus of  FIGS. 1   a  and  1   b  comprises a flexible oblong pneumatic actuator  1  (“Fluid Muscle”, Festo AG, Esslingen, Germany; inner diameter 20 mm, length 60 mm; model DSMP-20-550N) of the kind disclosed in U.S. Pat. No. 6,349,746 B1. A reference number provided with an asterisk indicates that the referenced element is physically changed by inflation of a actuator or is the inflated actuator. By hooks  2 ,  3  extending in opposite directions from head pieces  4 ,  5  the actuator  1  is attached to eyes  6 ,  7  mounted at opposite short sides of a glass fibre reinforced polyamide back plate  8  on which a the chest  20  of a patient under cardiopulmonary resuscitation is resting in a recumbent position. The actuator  1  partly encloses the chest  20  at the height of the sternum  21 . In this mounted state the actuator  1  is bent so as to form an inverse U. The central portion of the actuator  1  corresponding to the base of the inverse U is disposed in a transversal slot  9  in the upper face of an generally rectangular base plate  10  of same material as the back plate  8  ( FIGS. 1   c ,  1   d ). During inflation and deflation portions of the actuator&#39;s  1  outer face glide in the slot  9 . To facilitate gliding the slot  9  surface should be as smooth as possible and preferably of a material or covered by a coat of low friction. A suitable coat material is Teflon® or another polyfluorinated hydrocarbon polymer. From the lower face of the base plate  10  extends a circular compression pad  11  provided with a flexible circumferential lip (not shown) at its lower face, which abuts the breast of the patient above the sternum  21 . A short radial pneumatic connection pipe  12  extends from one head piece  4 . Compressed air for inflating the actuator  1  is adduced by a flexible high-pressure air hose  13  mounted at the pipe  12 . 
     In  FIG. 1   b  the actuator  1 * is shown in a state inflated by air of 5 bar. The actuator  1 *, which has been inflated against the resistive force of the chest  20  of about 350 N, is shortened by about 16%. Thereby the chest  20 * has been compressed to a depth of about 50 mm. The actuator  1 * can be deflated via the air hose  13  or a venting valve (not shown) arranged, for instance, at the opposite head piece  5 . 
     The second embodiment of the apparatus of the invention shown in  FIGS. 2   a - 2   c  of a patient shares its general design with that of the first embodiment of  FIGS. 1   a - 1   d . It comprises a back plate  108 , a pneumatic actuator  101  releasably fastened to the back plate  108  at its both ends, a base plate  110  and a compression pad  111 . It differs from the first embodiment in that the actuator  101 , except for its end portions, is disposed in shielding tube  130 . The aim with the shield tube  130  is to protect the patient from damage by an exploding actuator  101 *, and also from contact with the moving actuator  101 ,  101 *. The shielding tube  130  is disposed in a slot  109  of the base plate  110  corresponding to the slot  9  of the embodiment of  FIGS. 1   a - 1   d . The shielding tube  130  is held in the slot  109  clamped by the actuator  101 ,  101 * but can also be attached to the slot wall by, for instance, an adhesive or welding. The inner face of the shielding tube  130 , against which the actuator  101 ,  101 * glides during inflation and deflation, should have a low-friction surface. The shielding tube  130  of  FIGS. 2   a - 2   c  is somewhat flexible to allow it to adapt to the slightly changing angle of the actuator  101 ,  101 * legs during a compression cycle. Alternatively the shielding tube  130  can be of a stiff material provided that its lumen is wide enough to accommodate the changing angle and diameter of the actuator  101 ,  101 * over a compression cycle. 
     The third embodiment of the apparatus of the invention shown in  FIGS. 3   a  and  3   b  comprises two pneumatic actuators  201 ,  231  of equal length and properties (inner diameter: 20 mm; length: 40 cm). The actuators  201 ,  231  have hooks  203 ,  202  extending axially from their first ends  205 ,  204 , by which they are attached to eyes  207 ,  206  fixed to and extending from opposite short sides of a rectangular back plate  208 . From the second ends of the actuators  201 ,  231  rods carrying terminal eyes  226 ,  225  extend in axial directions. The eyes  226 ,  225  are mounted on bars  228 ,  227  bridging slits  230 ,  229  in a base plate  210 . The rod  239  of a compression pad  211  is mounted displaceably in a central through bore of the base plate  210 , of which a portion extending from the upper end is threaded. Compressed air is fed to the actuators  201 ,  231  by branches  213 ,  223  of a flexible high pressure gas hose. The apparatus is mounted to the patient&#39;s chest  220  in the following manner: the compression pad  211  with the rod  239  disposed in the base plate  210  is placed on the patient&#39;s chest and centred on the sternum. It is held there while sliding the base plate  210  upwards along the rod  239  until further displacement is hindered by the straightened actuators  201 ,  231 . A threaded stop  222  is screwed into the bore until stopped by the end face of the rod  239 . This arrangement allows to adapt the apparatus to the size of the chest  220  of an individual patient. In the inflated state of the actuators  201 *,  231 * shown in  FIG. 3   b , the compression pad  211  has compressed the chest  220 * of the patient by about 50 mm at a driving gas pressure of 4 bar. 
     In a fourth embodiment of the apparatus of the invention shown in  FIG. 4  comprising a single actuator  301 , the hook means of the embodiments described in the foregoing are replaced by a polyester belt  333 . One end of the belt  333  is fastened at an eye  305  of one end piece  303  of the actuator  311 . A belt portion extending from the other end of the belt  333  is provided with a row of holes  335 , by any of which the belt  333  can be fasted at a mandrel  332  extending radially from the other end piece  304 . The intermediate portion of the belt  333  is disposed in a channel  336  extending from one short side of the back plate  308  to the other side. Most of the load working on the belt  333  is taken up by deflection pins  307 ,  306  disposed in a manner corresponding to the eyes  7 ,  6  of the first embodiment. Reference numbers  310 ,  311  designate a base plate and a compression pad of same design as those of the first and second embodiments. 
     In a fifth embodiment of the apparatus of the invention similar to that of  FIGS. 3   a ,  3   b  in respect of the use of two actuators of same size and properties, the actuators, of which only one actuator  401 * is shown in  FIG. 5  in an inflated state, are working against a resiliently compressible means. One reason for this arrangement is to make the first inflated actuator  401 * and the second inflated actuator (not shown) return to their original non-inflated configuration as soon as they are deflated. In the embodiment of  FIG. 5 , the resiliently compressible means is a steel coil  440  held between first and second support flanges  441 ,  442  of the actuator&#39;s  401  first and second end pieces, respectively. A hook  405 , by which the apparatus is fastened at an eye  407  of the back plate  408 , is mounted in a central bore of the first end piece. The female part  426  of a ball-and-socket joint is mounted at the actuator&#39;s  401 * second end piece, while the male part  428  is mounted in a threaded bore a base plate  410 . A conduit  413  in the base plate  410  provides communication between a source of compressed air and the actuator  401 *. The ball-and-socket joint of the embodiment can be exchanged for a series LS quick coupling of a width of 23 mm (Carl Kurt Walther GmbH &amp; Co. KG (Haan, Germany) the nipple and the coupling housing provided with threaded end portions matching the thread of an axial bore of the second end piece and of the bore in the base plate. The coupling housing and the nipple may be mounted at the base plate or the actuator, respectively. 
     A CPR apparatus of the invention that comprises only one pneumatic actuator, such as the apparatus of  FIGS. 1   a - 1   d , can be provided with a resiliently compressible means of the aforementioned kind by, for instance, arranging one compressible steel coil each around the arms of the U-formed actuator. At their one end the coils are supported by a flange of the respective end piece. At their other end the coils are supported by a flange mounted at lateral sections of the base plate, in particular close to the respective end of the groove in which the base of the actuator is disposed. Alternatively a single compressible steel coil extending from a support flange of one end piece to a support flange the other end piece could be used, an intermediate section of the coil being disposed in the groove of the base plate. 
     The fifth embodiment of the apparatus of the invention illustrated in  FIGS. 6   a ,  6   b  corresponds generally to that of  FIGS. 1   a ,  1   b . The chest  520  of the patient is strapped by a single actuator  501  to a back plate  508  but without any interposed element. At both ends the actuator  501  is fastened to eyes  506 ,  507  extending laterally from the back plate  508  by means of hooks  502 ,  503  extending from head pieces  504 ,  505  of the actuator  501 . Compressed air is adduced to the actuator  501  via a flexible tube  513  mounted at a connection pipe  512  of head piece  504 . The actuator  501  is vented by a solenoid valve  515  arranged at the other head piece  515 ; an advantage with this arrangement is that the temperature of the actuator  501  does rise less than if it is vented via the same end. In its expanded state  501 * the actuator has shortened enough to compress the chest by about 30 mm which, while not optimal, is an acceptable compression depth. A major advantage of this and the following embodiments is its simplicity. 
     The sixth embodiment of the apparatus of the invention illustrated in  FIG. 7  with its actuator  601 * in a an expanded (active) state comprises a compression plate  611 * disposed between the chest  620 * of a patient and the actuator  601 * in a bended state. The resiliently flexible oblong compression plate  611 , which is shown in a top view and a side view in  FIGS. 7   a  and  7   b , respectively, in an unloaded (not bended) state, is substantially flat except for a longitudinally extending slot  612 . In a mounted state the actuator  601  is disposed in the slot  612  to keep the compression plate  611  from moving in a cranial or opposite direction in respect of the actuator  611 . The resilient nature of the compression plate  611 , which seeks to regain its original flat state from the bended state shown in  FIG. 7 , supports the actuator in assuming its full length or inactive state  611  at the end of the compression phase. Elements identified in  FIG. 7  by reference numbers  604 ,  608 ,  615  correspond to elements  504 ,  508 ,  515  in  FIG. 6   a.    
     Variations of the compression plate  611  are shown in  FIGS. 8 ,  8   a ,  8   b , and  FIG. 9 , respectively. The first variation is U-formed in a longitudinal section D-D and comprises a centrally disposed slot  714  in which the actuator  701  can be disposed. The wings  712 ,  713  extending from either side of the base  711  increase the resilient spring action of the compression plate when mounted in-between the actuator  701  shown in an expanded state  701 * in  FIG. 8   b . In the mounted state of the compression plate the wings  712 *,  713 * are bent downwards. When the compressed air is vented from the actuator  701 *, the wings  712 *,  713 * flap back to their original state  712 ,  713 , thereby lifting up and thus extending the actuator  701 *. The V-formed variation of the compression plate  811 ,  812 ,  813  shown in  FIG. 9  exerts an uplifting effect on an actuator also by its central portion  811  when mounted between the actuator and the chest of a patient in a manner corresponding to that of compression plate  711 . 
     In the pneumatic control scheme for an apparatus of the invention illustrated in  FIG. 10  compressed air is provided from a gas flask  50  to expander module  51  in which the gas is expanded to the driving pressure. The driving pressure can vary depending on the length and diameter of the actuator and on the design of the apparatus, but will generally be in the interval of from about 2 to about 4.5 bar. Via a flexible pressure line  52  the driving gas is adduced to the apparatus  60 , where it passes a safety valve  53  that is mechanically vented at a selected pressure. A 3/2 solenoid-actuated valve  54  controlled by a timing module  57  optionally comprising a pressure sensor  58  supplies driving gas to one or several actuators of which only actuator  56  is shown. A self-sealing quick-coupling  55  is provided in the line between the 3/2-valve  54  and the actuator  56 . Over a compression/decompression cycle the driving gas supply and control system of  FIG. 6  provides driving gas to the actuator  56  to make it expand and thereby displace the compression pad of one of the aforementioned embodiments in contact with the sternal region of a patient towards the heart of the patient, thereby providing heart massage and expelling air from the lungs. The actuator  56  is kept in an expanded state for a selected period of time and then deflated by via the venting outlet of the 3/2 valve  54 . The 3/2 valve  54  then is switched to the starting position of a new compression/decompression cycle. The actuator  56  can also be driven in a manner, in which equilibrium between the pressure of the driving gas provided to the actuator  56  and the pressure of the driving gas set by the expander module is not established. In such case a higher driving gas pressure than at equilibrium conditions will be used but will be provided to the actuator  56  only during an initial portion of the compression phase. An alternative exhaust path is indicated in broken lines. In the alternative path the actuator is vented, optionally to an intubation set or a breathing mask (not shown) via its end opposite to that coupled to valve  55  via a solenoid actuated exhaust valve  59  controlled by the timing module  57 ; in this variation the exhaust function of valve  54  is inoperative.