Abstract:
Trans-esophageal cardiac compression is performed during cardiopulmonary resuscitation by introducing into the esophagus a tube ( 12 ) having a distal inflatable member, such as a balloon ( 20 ). The balloon ( 20 ) is positioned in the esophagus ( 48 ) at the level of the ventricles of the heart ( 50 ). A rapidly cycling pump ( 16 ) (such as a compressible bag) is attached to the tube ( 12 ), and used to inflate and deflate the balloon ( 20 ) on the tube ( 12 ). As the balloon ( 20 ) inflates, it compresses the ventricles against the sternum ( 54 ), increases the transmural pressure across the ventricular wall, and propels blood out of the heart ( 50 ) into the aorta and pulmonary arteries. The balloon ( 20 ) is inflated and deflated at a rate of approximately 60 cycles to 80 cycles per minute to maintain perfusion of the heart, brain and other vital organs until more definitive therapy can reestablish the contractile activity of the heart. The balloon ( 20 ) can be inflated and deflated by a handheld pump ( 16 ), or by a rapidly cycling gas pump ( 100 ). A particular embodiment of the pump includes a larger volume pump that is driven by a smaller volume drive pump which cycles rapidly to force gas into and out of the balloon.

Description:
This application is a §371 of PCT/US97/10661 filed Jun. 18, 1997 which claims §119(e) of Provisional application 60/020,048 filed Jun. 18, 1996, now abandoned. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to methods and devices for performing cardiopulmonary resuscitation, and is more specifically related to intrathoracic cardiac compression during cardiac resuscitation. 
     BACKGROUND OF THE INVENTION 
     Cardiopulmonary resuscitation (CPR) is widely used in clinical medicine to maintain perfusion of vital organs during episodes of sudden cardiac arrest when the heart stops spontaneously beating (asystole). Any period of prolonged asystole (such as from ventricular fibrillation) can cause irreversible hypoxic damage to vital end organs (such as the brain and heart) that are not perfused during the asystolic episode. CPR can often maintain a sufficient level of arterial oxygenation and blood flow to avoid irreversible end organ damage and death, at least until spontaneous cardiac activity resumes or external ventricular defibrillation converts the cardiac rhythm to a more effective electrocardiographic pattern. 
     The components of CPR usually include external cardiac compressions and pulmonary ventilation. The external cardiac compressions are achieved by repetitively forcing the sternum against the heart to compress the heart between the sternum and vertebral column. Manual chest compressions also produce a positive intrathoracic pressure and enhance emptying of the heart, possibly by reducing afterload of the left ventricle. Cardiac compressions are usually only interrupted to administer mouth-to-mouth or mechanical ventilation, which cyclically inflates the lungs to achieve oxygenation of the blood, or to attempt electrical cardioversion of the fibrillating heart. 
     Although CPR has improved initial survival of episodes of sudden cardiac death, its effectiveness is less than optimal. External compression of the heart, for example, is not as effective as surgically opening the chest and performing direct manual compression of the heart. Several studies have estimated that in-hospital CPR is effective in only 10-15% of patients. Open chest cardiac massage can better achieve normal or supranormal cerebral blood flows, which are associated with improved neurologic recovery from the cardiac event. Such dramatic surgical intervention is not usually available, however, and even in a hospital setting is often impractical or not feasible. The inability of closed chest CPR to maintain adequate levels of cerebral blood flow is the principal reason for the low survival rates and poor neurologic recovery often associated with CPR. Moreover, external chest compressions frequently cause significant morbidity, such as broken ribs or a fractured sternum. 
     Both external (closed chest) and surgical (open-chest) techniques of cardiac compression can be performed manually, or with the aid of mechanical devices. With either technique, the goal is to maintain artificial circulation, including perfusion of cerebral and coronary arteries, until spontaneous cardiac activity can be restored. An example of an intrathoracic cardiac massager is shown in U.S. Pat. No. 3,496,392, which discloses an inflatable bladder for insertion between the sternum and heart. After intrathoracic placement, the inflatable bladder is cyclically inflated and deflated to achieve cardiac compression. 
     U.S. Pat. No. 3,233,607, U.S. Pat. No. 3,478,737, U.S. Pat. No. 4,536,893, U.S. Pat. No. 5,119,804 and U.S. Pat. No. 5,383,840 all disclose mechanical devices that surround and engage the ventricular regions of the myocardium to provide auxiliary cardiovascular support for impaired myocardium. U.S. Pat. No. 5,385,081 shows a similar device, but the device is placed in the intrapericardial space. U.S. Pat. No. 5,484,391 describes a substernal heart massaging plunger that is surgically inserted through an intercostal space to compress the heart. 
     Although these and other heart compressing devices effectively achieve arterial perfusion, they require surgical placement that is often unavailable or impractical in emergency outpatient or clinical settings. Moreover, surgical procedures performed under emergency conditions often inadvertently and unavoidably introduce infectious pathogens into the patient, which can frustrate or prevent recovery. 
     Other devices have been developed to assist with external cardiac compression, and that avoid the necessity of surgical placement. U.S. Pat. Nos. 5,490,820 and 5,453,081, for example, both disclose external, vest-like devices that are worn by a patient to provide external chest compressions that promote movement of blood from the heart. 
     None of these devices have been able to provide an approach that combines the effectiveness of intrathoracic cardiac compression with the convenience and availability of external compression devices. 
     Accordingly, it is an object of this invention to provide an apparatus and method that achieves superior cardiac compression during episodes of ineffective cardiac contraction or asystole. 
     Yet another object is to provide such an apparatus and method that performs cardiac compression without the necessity of surgical intervention. 
     These and other objects of the invention will be understood more clearly by reference to the following detailed description and drawings. 
     SUMMARY OF THE INVENTION 
     The foregoing problems have been overcome by providing a device for performing intrathoracic transesophageal cardiac compression. The device includes an esophageal tube of suitable size and flexibility to be introduced into the esophagus. An inflatable compression member (such as a balloon) is provided on the esophageal tube. The esophageal tube is of sufficient length to allow the inflatable member to be introduced into the esophagus to a distance that disposes the inflatable member between the heart and vertebral column. The inflatable member has sufficient volume to compress the heart an effective volume (for example 200 cc) to perform therapeutically effective transesophageal cardiac compressions during CPR. A pump connected to the esophageal tube cyclically inflates and deflates the inflatable compression member at a sufficient frequency to restore adequate circulatory blood flow. 
     In a disclosed embodiment, the inflatable member is a distensible bladder or balloon that can expand to a volume of approximately 200-250 cc. The pump may be a hand-held resilient collapsible and expandable pumping chamber that is compressed to expand the inflatable member, and allowed to expand to deflate the inflatable member. The hand-held pump includes a check valve that allows air to be drawn into the pumping chamber if the pressure in the chamber exceeds a preselected negative value, and allows air to be expelled from the pumping chamber if pressure in the chamber exceeds a preselected positive pressure. Alternatively, the pump can be a rapidly cycling electrically powered or hydraulic actuated air pump. Another alternative method of cyclical inflation of the esophageal balloon is the use of a bottle of compressed air with a pressure regulated valve. 
     In one embodiment, the rapidly cycling pump includes a reciprocating pump piston that defines a variable volume gas chamber, the volume of which is varied by movement of the pump piston. The pump piston is driven by a separate drive piston, which is reciprocated in response to a hydraulic signal that can be rapidly changed to cycle the pump at the desired frequency. A delay mechanism can prolong the pumping cycle, for example by interposing a delay of approximately 250-300 milliseconds, between deflation and inflation of the esophageal balloon. This delay allows end diastolic filling of the heart to take place more efficiently than would occur if the pump constantly cycled without a pause between inflation and deflation of the balloon. 
     The invention also includes a method of performing transesophageal cardiac compressions by providing the inflatable member on an esophageal tube, and then introducing the inflatable member into the esophagus a sufficient distance to dispose the inflatable member between the heart and vertebral column. The inflatable member is then cyclically inflated and deflated a sufficient volume (for example 200 cc) at a sufficient rate (for example 40-80 cycles per minute, preferably 60-80 cycles per minute) to compress the heart during CPR. The inflatable member is preferably positioned at the level of the ventricles, such that expansion of the inflatable member compresses the ventricles against the sternum to expel blood into the aorta. Subsequent deflation of the member allows the ventricles to expand, which draws blood into the heart for subsequent circulation secondary to venous pressure and blood flow from the superior and inferior vena cava via the right auricle. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a view of the cardiac compression device of the present invention, portions of the tubing being broken away for purposes of illustration. 
     FIG. 2 is a schematic view, in sagittal section through the head and thorax, illustrating the position of the cardiac compression device in use. 
     FIG. 3 is a front view of the thorax, illustrating the desired placement of the compression device. 
     FIG. 4 is a transverse schematic sectional view through the thorax, at the level of the ventricles, illustrating placement of the cardiac compression device. 
     FIG. 5 is a view similar to FIG. 4, but showing the cardiac compression device in an inflated condition. 
     FIG. 6 is a perspective view of portions of an embodiment of a rapidly cycling pump that is used to inflate and deflate the cardiac compression device. 
     FIG. 7 is a schematic view of the hydraulic system that controls the drive pump of FIG.  6 . 
     FIG. 8 is a cross-sectional view of the pump taken along line  8 — 8  in FIG. 6, and wherein advanced positions of pump components are shown in phantom lines. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     A device  10  for performing transesophageal cardiac compression during CPR is shown in FIG. 1 to include an esophageal tube  12  of suitable size and flexibility to be introduced into the esophagus. Such a tube may be a large bore nasogastric tube (for example 18-24 French plastic tubing) or a 15 mm diameter endotracheal tube. The tube  12  may be of varying lengths, but is preferably at least 40 cm long. A portion of the tube  12  in FIG. 1 is cut away for purposes of depiction, but the actual tube is a clear plastic member with a continuous cental bore therethrough. 
     Tube  12  has a proximal end  14  that is connected to a pump  16 , and a distal end  18  that is provided with an inflatable member  20 . The inflatable member  20  is a balloon or distensible bladder that is sealed circumferentially to tube  12  above and below a pair of orifices  22 ,  24  that communicate with the continuous bore of the tube. Air in the tube communicates with the interior of the sealed balloon through the orifices  22 ,  24 . 
     The pump  16  is a hand-held resilient collapsible and expandable chamber pump, such as a conventional ambulatory ventilation bag  30 . The bag  30  is made of a resilient collapsible and expandable material that encloses an air chamber of variable volume. Bag  30  extends between and is suspended by a pair of opposing structural end members  32 ,  34 . Member  32  is a solid plastic or metal top cap that supports an air control mechanism  36  (described below), while member  34  is a solid or ring shaped bottom. The variable volume of bag  30  is illustrated in FIG. 1, wherein the expanded volume of the bag  30  is shown in solid lines, and a compressed condition of the bag is illustrated in phantom lines. Bag  30  is compressed manually, for example by squeezing the bag at a middle section to decreases the volume of the enclosed chamber, and expel air from the chamber. 
     Air control mechanism  36  includes a generally L-shaped connector  40  that communicates at one end with the interior of bag  30  and at the other end with flexible tube  12 . The L-shape of connector  40  allows the bag  16  to be held in a comfortable position relative to tube  12  during use when the patient is in a supine position. A check valve  42  communicates with connector  40 , and allows air to be drawn in through valve  42  when a negative pressure in bag  30  exceeds a preselected value, and allows air to be expelled through valve  42  when a positive pressure in bag  30  exceeds a preselected value. As long as pressures in bag  30  are within the preselected range, all air flow occurs through connector  40  into tube  12 . 
     The device  10  is used during CPR to provide intrathoracic transesophageal cardiac compressions. In use, the device  10  is provided with the balloon  20  in its deflated condition. Pump  16  may be attached to the tube prior to insertion of the tube  12  into the esophagus, or attached to the tube subsequent to insertion. With the patient in the prone position, an estimate of the length of tube needed to position the balloon  20  can be made by placing the balloon externally on the chest at the level of the xiphoid and determining the length of tube that reaches from the xiphoid to the lips of the patient. Then the mouth is opened and the distal tip  18  of the tube is advanced into the posterior oropharynx  46  (FIG. 2) and then into the esophagus  48 . Advancement of the tube is continued until the tube is advanced the estimated predetermined length, at which position the balloon is positioned in the esophagus  48  between the heart  50  and one or more vertebrae  52  of the spinal column. A preferred position of the balloon  20  is shown in the front view of FIG. 3, wherein the balloon is positioned at the level of the ventricles of the heart. The sternum  54  is shown anterior to the heart in FIGS. 2 and 3. 
     Once the balloon is in its desired position, and pump  16  is attached to tube  12 , the resilient bag  30  of pump  16  is manually grasped and compressed. The compressed condition of the bag  30  is shown in broken lines in FIG.  1 . As the bag  30  is compressed, pressure in the bag is increased and air is expelled out of pump  16 , into tube  12 , through holes  22 ,  24 , and into the balloon  20 . Air is expelled from bag  30  as it is collapsed, which fills the balloon  20  to the shape shown in broken lines in FIGS. 1 and 2. In the preferred embodiment, bag  30  in compressed to expel a sufficient volume of air to fill balloon  20  to a volume of approximately 200 cc or more. The 200 cc volume of the inflatable member is selected because that is the approximate stoke volume of a normal heart during systole. 
     Balloon  20  is then subsequently deflated to its original volume by releasing pressure that was exerted on bag  30 . The resilient bag expands to its original volume, which creates a negative pressure in bag  30  to draw air out of the inflatable member and into the bag  30 . The balloon  20  is thereby deflated to its residual volume. 
     The transesophageal action of the inflatable member is shown in the transverse thoracic sections of FIGS. 4 and 5. In FIG  4 , the balloon  20  (in the deflated condition) is positioned at the level of the ventricles between vertebra  52  and heart  50 . This view shows the sternum immediately anterior to the heart. The balloon  20  is expanded by compressing bag  30  of pump  16  (FIGS.  1  and  2 ), which expands the distensible esophagus to a volume of at least about 200 cc, as shown in FIG.  5 . This enlarged esophageal volume expands to fill an area between vertebra  52  and heart  50 , and compresses the ventricles of heart  50  between balloon  20  and sternum  54 . Compression of the ventricles forces blood into the aorta and coronary arteries for perfusion of vital organs. Expansion and contraction of the balloon  20  is cyclically repeated, for example at 60-80 cycles per minute, to continue perfusion of vital organs until the heart can resume it rhythmic activity. 
     Although the embodiment of this specification operates with a hand compressed bag, any other convenient means can be used to cyclically inflate and deflate the balloon  20 . A rapidly cycling centrifugal or piston pump may, for example, be substituted for the bag  30 . 
     A particular embodiment of a pump  100  that is suitable for automatically inflating and deflating the bag is shown in FIGS. 6-8. Pump  100  (FIGS. 6 and 8) includes a large diameter air (or other gas) container, which in the disclosed embodiment is a cylinder  102  having a vent  103  to the atmosphere, and a coupling  104  connecting the cylinder  102  to a pump replenish valve  106 . Valve  106  has a vent  108  for selectively introducing additional air (or other gas) into the pumping system if it is needed. Valve  106  is in turn connected to the tube  12  of the resuscitation device  10 , so that pump  100  can introduce air into, and remove air from, inflatable member  20 . 
     Pump  100  is driven by a drive pump  120  that is illustrated in FIGS. 6-8. The pump  120  includes a drive cylinder  122  within which can reciprocate an enlarged piston head  124  (FIG. 8) having a peripheral seal  126 . A rear piston rod  128  extends through the rear face of cylinder  122 , an a front piston rod  130  extends through the front face of cylinder  122 . Front rod  130  has an externally threaded tip  131  that is fixed to a front lever plate  132 , which plate extends perpendicular to the longitudinal axis of rod  130 . Threaded tip  131  extends through plate  132  to engage an internally and externally threaded adaptor  134  that engages an internally threaded end of a larger diameter piston rod  136  that drives a piston head  138  in pump cylinder  102 . A peripheral seal  140  around piston head  138  establishes a fluid tight relationship between piston head  138  and the walls of cylinder  102 , while an internal seal  142  in front wall  144  of cylinder  102  maintains a gas tight relationship between piston rod  136  and wall  144 . 
     A pumping chamber  146  is defined within cylinder  102  between piston head  138  and a front wall  148  of the cylinder. Chamber  146  contains a desired volume of gas (for example 250 cc) when the piston head  138  is in the fully retracted position shown in solid lines in FIG.  8 . The volume of chamber  146  can be varied by moving piston head  138  between the position shown in solid lines in FIG. 8, and the advanced position shown in phantom lines and designated  138   a . Reducing the volume of pumping chamber  146  expels a volume of gas proportional to the stroke of the piston head  138  (e.g. 200 cc) out of chamber  146  and into the cardiac compression device. 
     A rear lever plate  150  is fixed to the threaded tip of rear piston rod  128 , such that plate  150  extends perpendicular to the longitudinal axis of piston rod  128 . A seal  152  between rear piston rod  128  and the wall of drive cylinder  122  prevents gas in cylinder  122  from escaping. A forward gas coupling  154  communicates with the interior of cylinder  122  behind piston head  124 , while a reverse gas coupling  156  communicates with the interior of cylinder  122  forward of piston head  124 . Hence gas introduced through forward coupling  154  drives piston head  124  and its associated rods  128 ,  130  in the forward direction  158 , while gas introduced through reverse coupling  156  drives piston head  124  and its associated rods in the reverse direction  160 . 
     A shock absorber  162  (FIGS. 6 and 8) is positioned in the path of movement of rear lever plate  150  so that plate  150  hits a pin  164  of the shock absorber near the fully reverse position of plate  150 , shown in solid lines in FIG.  8 . The shock absorber slows the velocity of the reverse movement of the drive pump piston, and therefore introduces a short delay between the reverse movement of the drive piston  124  and its subsequent forward movement. This delay provides a pause between pumping cycles to allow better end diastolic filling of the heart, as explained below. 
     As illustrated in FIGS. 6-8, a rear three way poppet valve  170  is positioned at the forward end point of the path of movement of rear plate  150 , designated  150   a  in phantom lines in FIG. 8. A front three way poppet valve  172  is also positioned at the rearward end point of the path of movement of front plate  132 . Hence rear plate  150  depresses an actuator  174  of valve  170  when piston  124  of drive pump  120  has moved to its forwardmost desired position, and plate front  132  depresses an actuator  176  of valve  172  when piston  124  has moved to its rearwardmost desired position. Actuation of rear valve  170  sends a pulse of 80 psi gas to a rear remote activator  178  of a five way valve  180 . Alternate actuation of front valve  172  sends a pulse of 80 psi gas to a front remote actuator  182 . The volume of the pump is set by the placement of valves  170  and  172 , which determine the stroke of piston  124 . 
     In operation, gas is supplied through a regulator  186  (FIG. 7) to valve  180  through line  190 . The supplied gas may be oxygen from an oxygen tank of the type used in hospitals and emergency vehicles, and may be supplied at a pressure of 80-3000 psi. The gas is supplied at a pressure of 80 psi in the disclosed embodiment. The pressure at which the gas is supplied to valve  180  helps determine the speed with which the pump operates. Higher pressures increase the speed with which the pump cycles, and in turn increases the frequency of cardiac compressions delivered to the patient. 
     The five-way valve  180  is in a position to allow the gas to move through line  192  and into forward coupling  154  to start the pumping cycle. Piston  124  in drive cylinder  122  (FIG. 8) is pushed in the forward direction  158 , which in turn advances rod  136  and piston head  138  in large pump cylinder  102  in forward direction  158 . As piston head  138  advances, approximately 200 cc of air is pushed out of cylinder  102  into tube  12  and pumping member  20  within the esophagus. Forward motion of piston head  138  is stopped at the position designated in phantom lines as  138   a , when rear plate  150  reaches the position shown as  150   a  and pushes actuator  174  to activate rear valve  170 . When rear valve  170  is actuated, it sends an 80 psi pulse of gas through line  194  to the rear remote activator  178 . This pulse of gas shifts the five way valve  180  such that gas being supplied through line  190  is now directed through line  196  instead of line  192 . 
     Gas directed through line  196  moves through reverse coupling  156  into cylinder  122  forward of piston head  124  when piston head  124  is in the position when in phantom as  124   a . The drive piston therefore moves rearwardly in the direction  160 , which in turn moves piston  138  in the reverse direction  160  within cylinder  102 , and opens valve  170  to vent activator  178 . As piston  138  retracts, it pulls air out of compression member  20  to deflate it, and allow the heart to expand. Near the end of the reverse stroke of piston head  124 , rear plate  150  contacts pin  126  of shock absorber  130  to slow the velocity of the reverse stroke, which adds some time (for example a few hundred milliseconds) to the cycle before the cycle starts again. 
     At the selected end point of the reverse stroke of drive pump  120 , front plate  132  contacts actuator  176  of front valve  172 , which sends an 80 psi pulse of gas through line  198  to the front remote activator  182 . This pulse of gas shifts valve  180  so that the supply gas is again directed through line  192 , and the pumping cycle begins again. This arrangement allows the gas pump  100  to be cycled rapidly (e.g. 60-100 cycles per minute) to deliver the appropriate number of compressions to the patient&#39;s heart). 
     A delay needle valve  200  may be interposed in line  198  to change the speed at which actuation of valve  172  changes the position of valve  180 . Similarly a delay needle valve  202  may be interposed in line  194  to change the speed at which actuation of valve  170  changes the position of valve  180 . The delay valves  200 ,  202  may therefore be used to control the cycle speed of the pump, which in turn controls the frequency of cardiac compressions. Velocity control needle valves  204 ,  206  on five-way valve  180  may also be used to control the velocity of drive pump cycles. 
     In the disclosed embodiment, cylinder  102  is a 2.5 inch (6.5 cm) diameter cylinder that holds a maximum of 250 cc gas in pumping chamber  146 . Cylinder  122  is a ¾ inch (2 cm) diameter cylinder. The stroke cycle produced by this pump is divided into approximately thirds, with about ⅓ of the cycle being a forward stroke to pump gas into the pumping member  20  to compress the heart, about ⅓ of the cycle being a return stroke to draw gas out of the pumping member to allow the heart to expand, and about ⅓ of the cycle being a pause to allow the heart to fill with blood during end diastole. In a disclosed embodiment, the period of delay is at least 250 milliseconds, for example 250-300 milliseconds. This type of cycle imitates the pumping action of the human heart, in which end diastolic filling is allowed to occur before another contraction of the heart begins. 
     The stroke volume of pump cylinder  102  is set by the position of three-way valves  170 ,  172 . Moving the valve  170  in the direction  160  (FIG. 8) shortens the paths of movement  210  and  212  of plates  132  and  150 , and the strokes  214  and  216  of piston heads  124  and  138 , because path of movement  210  of plate  150  will be shorter before actuator  174  is activated to start the reverse stroke. The stroke can similarly be lengthened by moving valve  170  in the direction of arrow  158 . Valve  172  can similarly be positioned to alter the position at which plate  132  actuates valve  172  to reverse the pump cycle. 
     If desired, inflation and deflation of the balloon  20  may be interrupted to intermittently ventilate the patient. Alternatively, ventilations may be carried out concurrently with cardiac compressions to take advantage of intrathoracic pressure fluctuations that assist in pumping blood from the heart. 
     As used in this specification, the term “fluid” includes a gas or liquid. 
     Having illustrated and described the principles of the invention in several preferred embodiments, it will be apparent to those skilled in the art that the invention can be modified in arrangement and detail without departing from such principles.