Abstract:
The invention relates to a device for and method of cardio-pulmonary resuscitation (CPR) involving cardiac compression of a patient&#39;s heart through expansion of the esophagus with an orally inserted balloon. Traditional CPR applies external pressure to the patient&#39;s sternum in an attempt to compress the heart thereby forcing blood flow through the heart. Such CPR is often ineffective or highly inefficient since the applied external force is dissipated as the force deflates the lungs and collapses the esophagus posterior the heart. The method of the invention expands the esophagus with a cyclically inflated and deflated balloon in the local area between the heart and the spine to exert a more effective local compression to the posterior of the heart. Preferably the lungs are inflated simultaneously to contain and further compress the heart during local esophageal compression. The method includes orally inserting an elongate esophageal insert having a distal tip and a proximal end to an inserted position where the tip is disposed within the esophagus posterior the heart. The insert includes an esophageal expansion balloon located on the tip for inflating and deflating the esophagus when supplied with tidal volumes of pressurized gas from an automatic cycling ventilator. The ventilator preferably is also fitted with an orally inserted tracheal tube with inflated sealing cuff to inflate the patient&#39;s lungs simultaneously with tidal volumes of pressurized gas.

Description:
TECHNICAL FIELD 
     The invention is directed to a novel device and method of providing cardiac compression during cardio-pulmonary resuscitation (CPR) to provide the necessary cardiac output for adequate circulatory perfusion by simultaneously inflating the patient&#39;s lungs and inflating an esophageal balloon orally inserted to a position posterior the patient&#39;s heart, and including an automatic ventilator for simultaneous lung and balloon inflation. 
     BACKGROUND OF THE ART 
     Cardio-pulmonary resuscitation involves the compression of the patient&#39;s heart by application of pressure squeezing the chambers of the heart in order to maintain at least a minimal degree of blood circulation after the patient suffers a heart attack or other condition which causes the heart to cease pumping. 
     A conventional CPR method involves vigorously applying external pressure with the practitioner&#39;s hands to the patient&#39;s chest. A significant level of skill is required to provide consistently timed compressions of sufficient strength to compress the heart and result in adequate perfusion. This method has the advantage that a trained person can apply CPR rapidly without external equipment. However, the retention of the skill has been shown to be somewhat limited over time if the practitioner does not have an opportunity to practice often. There are significant dangers inherent in this method such as the risk of fractured ribs, internal bruising or other complications. These disadvantages are recognized in the medical literature such as for example in Krischer Fine. Davis and Nagel: “Complications of Cardiac Resuscitation” Chest 1987; 92:287-291. 
     A second commonly used method of cardio-pulmonary resuscitation is the direct squeezing of the heart in an internal cardiac massage. Although this method provides improved blood perfusion, compared to the above described externally applied CPR method, obviously open chest heart massage is simply not feasible in rescue or ambulance field conditions due to the need for surgical intervention. Direct heart massage therefore is limited to use as a last resort in an emergency within hospital conditions. Due to the major surgical intervention required, open chest heart massage is of extremely limited application. 
     The most commonly used method of CPR where external pressure is applied on the chest has been analyzed in clinical studies and is reported to generate cardiac output by compression of the heart between the posterior aspect sternum and the interior aspect of the vertebral body. The external pressure on the chest flexes the sternum and ribs toward the spine and collapses the esophagus between the posterior aspect of the heart and the spine. For example, see: Kouwnehove, W. B; Jude, J. R: Knickerbocker G. G: “Closed chest cardiac massage”. J.A.M.A. 173: 1064, 1960. 
     Further research has put forward the conclusion that conventionally applied external cardio-pulmonary resuscitation does not generate blood flow through actual heart compression but rather increases intrathoracic pressure which generates blood flow. To date both theories remain controversial, namely whether the heart is actually compressed, or the external pressure increases intrathoracic pressure that generates blood flow independent of the heart. Further research has pursued the concept that a combination of increased intrathoracic pressure together with heart compression can be used to generate increased blood flow during CPR. Such research has been done using synchronous ventilation and externally applied cardiac compression theoretically combining these theories however with mixed results. See for example: Swenson, R. D; Weaver, W. D: Naskanen R. A., Martin. J: Dahlberg, S: “Hemodynamics in humans during conventional and experimental method of cardio-pulmonary resuscitation”, Circulation 1998; 78:630-639; and Chandra. N: Rudikoff, M; Weisfeldt. M. L: “Simultaneous chest compression and ventilation at high airway pressure during CPR” Lancet 1980; 1:175-178. 
     Further clinical research has shown that cardiac output can be achieved by applying external pressure to the heart during lung inflation. See: Beyar R: Kishon Y: Kimmel, E: Neufeld H: Dinnar U: “Intrathoracic and abdominal pressure variations as an efficient method for CPR: studies in dogs compared with a computer model”. Cardiovascular Resuscitation 1985; 19,6: 335-42; Beyar R: Kishon, Y: Neufeld, H: Dinnar, U: “CPR by intrathoracic pressure variations-in-vivo studies and computer simulation”. Angiology 1984; 35, 2: 71-78; and Robotham, J. L.: “Cardiovascular disturbances in chronic respiratory insufficiency”. American Journal of Cardiology 1981; 47,4:941-949. 
     It is an object of the invention to combine the positive aspects of the above theories and existing methods of CPR in a novel method which produces cardiac output and blood circulation during CPR in a manner with consistent results, provides improved blood perfusion, can be applied in a simple manner and is minimally invasive. 
     It is a further object of the invention to provide a new method of CPR with application that provides predictable consistent results independent of the particular skills of the CPR practitioner and independent of the physical characteristics of the patient. 
     It is a further object of the invention to provide a novel method of CPR that can be operated automatically thereby freeing paramedics to perform other necessary medical functions. In contrast, conventional CPR methods require the fall attention and both hands of the CPR practitioner. 
     It is a further object of the invention to provide an easily used, low cost device, which ideally includes disposable components to minimize the risk of cross-infection, and includes an automatic patient ventilation device which can be independently used for ventilation when heart operation recommences, or in other paramedic operations where cardiac arrest is not diagnosed. 
     Further objects of the invention will be apparent from review of the disclosure and description of the invention below. 
     DISCLOSURE OF THE INVENTION 
     The invention relates to a device for and method of cardio-pulmonary resuscitation (CPR) involving cardiac compression of a patient&#39;s heart through expansion of the esophagus with an orally inserted balloon. 
     Traditional CPR applies external pressure to the patient&#39;s chest at the sternum in an attempt to compress the heart thereby forcing blood flow through the heart. This prior art CPR method is often ineffective or highly inefficient since the applied external force is dissipated as the force deflates the lungs, flattens the chest cavity and collapses the esophagus posterior the heart. 
     The method of the invention expands the esophagus with a cyclically inflated and deflated balloon in the local area between the heart and the spine to exert a more effective local compression to the posterior of the heart. Preferably the lungs are inflated simultaneously to contain and further compress the heart during local esophageal compression. 
     Specifically, the method includes orally inserting an elongate esophageal insert having a distal tip and a proximal end to an inserted position where the tip is disposed within the esophagus posterior the heart. The insert includes an esophageal expansion balloon located on the tip for inflating and deflating the esophagus when supplied with tidal volumes of pressurized gas from an automatic cycling ventilator. The ventilator preferably is also fitted with an orally inserted tracheal tube with inflatable tracheal sealing cuff to simultaneously inflate the patient&#39;s lungs with tidal volumes of pressurized gas. 
     Further details of the invention and its advantages will be apparent from the detailed description and drawings included below. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In order that the invention may be readily understood, one preferred embodiment of the invention will be described by way of example, with reference to the accompanying drawings wherein: 
     FIG. 1 is a perspective view of a combined esophageal tube (longer tube) and tracheal tube (shorter tube) the upper ends of which remain protruding from the patient&#39;s mouth with connectors for attachment to an automatic ventilator, the lower ends of which include a deflated esophageal balloon and a deflated tracheal sealing cuff respectively. 
     FIG. 2 is a view similar to FIG. 1 showing the esophageal balloon and the tracheal-sealing cuff fully inflated. 
     FIG. 3 is a longitudinal sectional view through a reclining patient&#39;s body showing the esophageal tube with inflated esophageal balloon posterior to the patient&#39;s heart and the tracheal tube with inflated tracheal sealing cuff surrounding the inserted end of the tracheal tube through which is conducted pressurized breathable gas in tidal volumes. 
     FIG. 4 is an open chest sectional view of the patient&#39;s cardio-pulmonary system with lungs deflated and esophageal balloon deflated. 
     FIG. 5 is a like open chest sectional view with the esophageal balloon inflated to apply compression to the heart also with lungs inflated to apply lateral pressure to compress the heart. 
     FIGS. 6A and 6B are a schematic view of the pneumatic circuits within the gas powered automatic ventilator used in association with the esophageal tube and tracheal tube to 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Referring to FIGS. 3,  4  and  5 , the invention provides a cardio-pulmonary resuscitation device for cardiac compression of the patient&#39;s heart  1  through expansion of the esophagus  2  immediately posterior the heart  1 . Preferably, the method and device include means to simultaneously inflate the patient&#39;s lungs  3  such as for example by insertion of a ventilating tracheal tube through the patient&#39;s trachea  4 . 
     FIG. 5 illustrates simultaneous inflation of the lungs  3  and the esophagus  2  with the device according to the invention whereas FIG. 4 illustrates the deflation of the esophagus and lungs thus forcing the patient&#39;s cardio-pulmonary system to inhale and exhale as well as providing cardiac compression for emergency blood perfusion. 
     Referring to FIGS. 1 and 2, the details of the portions of the cardio-pulmonary resuscitation device, which are inserted into the patient&#39;s body, are described below. 
     The inserted portions of the resuscitation device include an elongate esophageal tube  5  with a cushioned probe  6  at the distal tip  7 , in the embodiment shown disposed within an inflatable esophageal expansion balloon  8 . The esophageal tube  5  includes a connector  9  at a proximal end  10  for connection to an automatic ventilator  20  that pneumatically inflates and deflates the balloon  8 . As indicated in FIG. 3, the esophageal tube  5  is orally inserted using the cushioned probe  6  to guide the deflated balloon  8  to an inserted position wherein the distal tip  7  is disposed within the esophagus  2  posterior the heart  1 . The ventilator  20  (described below) is thereafter connected with a hose  19  to the connector  9  and the automatic ventilator  20  provides pulses or tidal volumes of compressed gas to alternately expand and contract the balloon  8  thereby exerting local external pressure on the posterior aspect of the heart  1 . 
     To show the depth of the tip  7  insertion within the esophagus  2 , the esophageal tube  5  includes visual indicators  11  as best shown in FIG.  3 . The balloon  8  when inflated serves to prevent regurgitation. 
     As mentioned above in respect of prior art and clinical studies, preferably the application of cardiac compression is accompanied by inflation of the patient&#39;s lungs. Whether one subscribes to the theory of improved perfusion to increase intrathoracic pressure or the theory of containing the heart laterally during localized cardiac compression, it would appear from clinical studies that improved cardiac perfusion results from simultaneous inflation of the lungs. 
     Accordingly, a preferred embodiment of the invention, as indicated in FIGS. 1,  2  and  3  includes a tracheal tube  12  disposed substantially parallel to the esophageal tube  5  having an insert end  13  through which breathable gas is conducted into the patient&#39;s lungs  3  from a ventilator attached with hose  19  to the protruding end  14  with ventilator connector  15 . To prevent accidental misconnection, the esophageal and tracheal connectors  9  and  15  are of different sizes or styles. The tracheal tube  12  has a length adapted for oral insertion together with the esophageal tube  5  to the inserted position shown in FIG.  3 . In the inserted position the insert end  13  of the tracheal tube  12  is disposed within the trachea  4  preferably below the level of the cricoid cartilage and above the carina. The visual indicators  11  on the tracheal tube  12  aid in determining proper insertion and may include markings for a variety of positions for different sized patients or children, for example. 
     In order to prevent the escape of breathable gas within the lungs  3 , the insert end  13  of the tracheal tube  12  includes a means to pneumatically seal the trachea  4  about the tracheal tube  12 . In the preferred embodiment illustrated, the pneumatic sealing device is illustrated as an inflatable cuff  16  which is inflated and deflated by pumping and exhausting air through an air supply tube  17  and a manual pump  18  with release valves in a manner similar to a commonly used blood pressure cuff and pump. 
     Referring to FIGS. 6A and 6B, the schematic view of an esophageal tube  5  and tracheal tube  12  is shown connected via flexible hoses  19  to an automatic ventilator  20 . The inner workings of the automatic ventilator  20  will be described below. 
     In a preferred embodiment the ventilator  20  is a completely gas powered automatic cycling ventilator which utilizes the power from pressurized gas taken in through a pressurized gas inlet  21  as the sole means for powering the ventilator  20 . In this manner, the reliance on electrical systems is eliminated. Malfunctioning batteries, short-circuits, explosion hazards, and other common problems with electrically powered ventilators are avoided. 
     The automatic ventilator  20  includes a internal pressure regulator  22  immediately downstream of the pressurized gas inlet  21  to provide the precise control over the gas pressure required for automatic ventilator applications. The automatic ventilator  20  includes an esophageal tube outlet port  23  and a tracheal tube outlet port  24 . 
     In operation, therefore the method of cardio-pulmonary resuscitation according to the invention proceeds as follow. Referring to FIG. 3, after diagnosing cardiac arrest in the patient the paramedic orally inserts the elongate esophageal tube  5  using a laryngoscope to observe the pharynx and the esophageal opening. The esophageal tube  5  and tracheal tube  4  are gradually inserted into the patient&#39;s mouth and the tip  7  of the longer esophageal tube  5  is guided with the cushioned probe  6  down the esophagus  2 . Under direct visualization through the laryngoscope, the esophageal tube  5  continues to be inserted until the insert end  13  of the tracheal tube  12  lies opposite the larynx. Both tubes  5  and  12  are further inserted until the tracheal tube  12  is positioned with insert tip below the level of the cricoid cartilage but above the carina, and the esophageal balloon  8  in a deflated state as shown in FIG. 1 is positioned posterior the patient&#39;s heart I as shown in FIG.  3 . 
     The curvatures of the tubes  5  and  12  as shown in FIGS. 1 and 2 are preferably designed to mimic the internal geometry of the human oro-pharynx to allow for easy insertion into the esophagus  2  and trachea  4  as shown in FIG.  3 . The tubes  5  and  12  are joined together for a distance of approximately  4  inches near the connectors  9  and  15  and bifurcate distally at an angulation to allow for an anatomical fit within the oropharynx once the tubes  5 ,  12  are fully inserted to reduce the risks of kinking and tube blockage. 
     Once inserted as illustrated in FIG. 3, the paramedic manually squeezes the flexible pump  18  to inflate the cuff  16  with air delivered via the air supply tube  17  to seal the trachea  4 . Thereafter, the connectors  9  and  15  are connected via flexible hoses  19  to the outlet ports  23  and  24  of the automatic ventilator  20 . 
     The automatic ventilator  20  delivers pulses of compressed gas tidal volumes through the esophageal tube outlet port  23  to selectively expand and contract the esophageal balloon  8 . Balloon  8  inflation applies pressure to the posterior aspect of the heart  1  and the heart  1  compresses within the thoracic cavity against the posterior aspect of the sternum. The balloon  8  inflation pressure is directed interiorly and laterally by the presence of a large vertebral body posterior the esophagus  2 . 
     Therefore, due to the anatomy of the esophagus  2  and vertebrae, the inflating and deflating balloon  8  is able to rhythmically exert local pressure on the heart  1  in a manner significantly superior to externally applied pressure on the sternum and rib cage. In addition, the automatic ventilator  20  provides control over the process which can be repeated, clinically proven and rendered highly predictable. The automatic ventilator  20  frees the paramedic to attend to other emergency requirements. 
     In a preferred embodiment, the automatic ventilator  20  also provides pulses of tidal volumes of compressed breathable gas to inflate the patient&#39;s lungs via the inserted end  13  of the tracheal tube  12 . As presently contemplated by the inventors, the preferred method includes inflating the patient&#39;s lungs with pressurized gas simultaneously with the pneumatic inflation of the esophageal balloon  8 , however clinical trials may show that other timing sequences are effective as well. The inflated lungs simultaneously compress the heart  1  laterally. This improved compression of the heart is sufficient to cause blood to be squeezed out of the heart and recirculated around the body. Oxygenation of the circulated blood takes place simultaneously due to the ventilation of breathable gas within the lungs  3 . 
     Between simultaneous pulses or tidal volumes of pressurized gas, the expiratory phase of operation permits the balloon  8  to deflate and lungs  3  to simultaneously deflate allowing the heart  1  to rebound and refill with blood ready for the next pulse or compression. 
     The automatic ventilator can be designed to provide simultaneous inflation of the lungs  3  and esophageal balloon  8  or can be designed to provide a delay between lung inflation and heart compression. The automatic ventilator  20  can also be designed to rapidly pulse at speeds which are not attainable through manual CPR methods. 
     It will be apparent as well that once the paramedic inserts the device and commences operation of the automatic ventilator  20 , the paramedic is free to attend to the other needs of the patient while visually monitoring the automatic ventilator. It will also be apparent that once the paramedic detects that the patient&#39;s heart  1  has recovered and commences pumping blood, the automatic ventilator  20  can be designed to cease operation of the balloon  8  and operate solely as a patient ventilator providing tidal volumes of the breathable gas through the tracheal tube  12 . 
     Turning th FIGS. 6A and 6B, the details of  1  preferred embodiment of the automatic ventilator  20  will be described. As previously mentioned, the preferred embodiment includes a gas powered automatic ventilator  20  independent of electrical controls or any other power or control source apart from the supply of pressurized gas through the pressurized gas inlet  21 . 
     An automatic circuit communicates between the pressurized gas inlet  21  and each of the outlet ports  23  and  24  for simultaneous automatic inflation of the esophageal balloon  8  via the esophageal tube  5  and the patient&#39;s lungs  3  via the tracheal tube  12 . The automatic circuit is supplied with pressurized gas from the inlet  21  via an automatic supply conduit  25  to a main on/off valve  26 . Output from the main valve  26  continues along conduit  27 . 
     An automatic esophageal output conduit  28  conducts pressurized gas between the main valve  26  and the esophageal outlet port  23  through the esophageal flow control valve  29  and mode switch  30 . Simultaneously, an automatic tracheal output conduit  31  conducts pressurized gas from the main valve  26  through the tracheal output port  24  through the tracheal flow control valve  32  and mode switch  33 . Mode switches  30  and  33  are illustrated in the OFF position wherein gas flow is prevented from proceeding to the ports  23  and  24 . When switches  30  and  33  are simultaneously rotated clockwise to a dual flow position, gas is simultaneously conveyed to the esophageal outlet port  23  from the esophageal output conduit  28  and to the tracheal outlet port  24  through the tracheal output conduit  31 . Further clockwise rotation of the switches  30  and  33  to a ventilation only position prevents flow to the esophageal outlet port  23 , while maintaining flow through the tracheal outlet port  24  in order to cease inflation and deflation of the balloon  8  while maintaining automatic ventilation through the tracheal tube  12  to the patient&#39;s lungs  3 . 
     The flow control valves  29  and  32  provide restriction of the passage of pressurized gas preferably by passing the pressurized gas through laser drilled holes in an indexable rotating disc. The disc is indexed between different sized of laser drilled holes to precisely determine the restriction opening and ensure precise control over the flow delivered through the valves  29  and  32 . 
     The automatic circuit also includes an automatic timing circuit which communicates between a bleed  34  downstream the main valve  26  and a main valve control chamber  35  via a frequency control valve  36  and a timing switch  37 . The timing of automatic pressurized gas pulses is provided as follows. To commence operation of the automatic circuit, the paramedic operator turns the switches  30  and  33  to one of the operating positions and opens a valve on a breathable gas cylinder (not illustrated) to deliver pressurized gas to the pressurized gas inlet  21 . The main valve  26  is spring-loaded normally open and pressurized gas continues through conduits  25 ,  27 ,  28 ,  31 , and hoses  19  to simultaneously pressurise the patient&#39;s airway and the inflatable balloon  8 . When the main valve  26  is an open position, a small amount of pressurized gas also proceeds through bleed  34 , filter  38  and conduit  39  to the frequency control valve  36 . The frequency control valve  36  resists the passage of pressurized gas preferably through restriction of an opening in an indexable laser drilled plastic disc. Pressurized gas proceeds through the frequency control valve  36  and conduit  40  to a control chamber of the timing switch  37 . When the volume of gas proceeding through the frequency control valve  36  is adequate to pressurise the control chamber of the timing switch  37 , the switch is activated to move from a inhale position to an exhale position. In the exhale position, pressurized gas can proceed from the regulator  40  through conduit  41  through the stem of the timing switch  37  to conduit  42  to pressurise the chamber  25  within the main valve  26  and close the main valve  26 . 
     When the main valve  26  is open, gas conveyed from bleed  34  maintains anti-lockup valves  51  closed. Over time, a sufficient amount of gas also passes through bleed  34 , conduit  39 , to frequency control valve  36 , to pressurize the control chamber of timing switch  37  and overcome the biasing force of a spring keeping the timing switch  37  normally in the inhale position. At this stage the timing switch  37  is shifted to an exhale position wherein gas is vented through conduit  42  from the main valve  26  to atmosphere via vent  44 . 
     When the main valve  26  is closed, the anti-lockup valves  51  vent pressurized gas from the tracheal port  24  and the esophageal port  23  to atmosphere. Pressurized gas within the control chamber of the timing switch  37  also slowly vents to atmosphere backwards through conduit  40 , frequency control valve  36 , conduit  39  to bleed  34 , conduit  27  and ports  23 ,  24 . In this manner, the cycling of the timing switch  37  serves to open and close the main valve  26  in a precisely controlled predictable manner. 
     The automatic ventilator  20  also preferably includes a continuous patient airway pressure circuit communicating between the pressurized gas inlet  21  and the tracheal outlet port  24  for maintaining gas pressure within the tracheal tube  12  and the patient&#39;s lungs  3  at above a selected minimum CPAP pressure when the automatic circuit main valve  26  is closed. The CPAP pressure is supplied by a CPAP supply conduit  45  delivering gas to the CPAP valve  46 . The CPAP output conduit  47  conducts pressurized gas between the CPAP valve  46  and the tracheal outlet port  24  through the CPAP control regulator  48 . The CPAP valve control conduit  49  communicates between the bleed  34  downstream of the main valve  26  and a CPAP valve control chamber  50 . 
     In operation, when the main valve  26  is open, a supply of pressurized gas escapes from the bleed  24  via conduit  49  to pressurise the CPAP valve control chamber  50  and close the CPAP valve  46 . When the timing switch  37  closes the main valve  26 , the CPAP valve control chamber  50  slowly vents through bleed  34 , conduit  27 , ports  23 ,  24  and anti-lockup valves  51 . When the CPAP valve control chamber  50  is vented to a sufficient degree, pressure drops within the chamber  50  and is insufficient to resist biasing force of a spring within the CPAP valve  46  that maintains the CPAP valve  46  normally open. The CPAP valve  46  opens delivering pressurized gas from the CPAP supply conduit  45  via conduit  47  to the tracheal tube outlet port  24 . CPAP control regulator  48  provides flow restriction to control the pressurisation of the tracheal outlet port  24  during exhale stage of the ventilation cycle. 
     The ventilator  20  also includes an alarm circuit in communication with the pressurized gas inlet  21  for initiating an alarm when the inlet gas pressure is below a selected minimum alarm pressure. An alarm valve  52  is supplied with pressurized gas via conduit  53 . Pressure sensing valve  54  is provided with unregulated supply gas direct from the gas inlet  21  (bypassing regulator  43 ) via conduit  55  to close valve  54  by pressurizing a control chamber against the pressure of a spring keeping the valve  54  in a normally open position. Pressurized gas passes through the control chamber of valve  54  from conduit  55  to conduit  56  to pressurized and close the (spring-loaded normally open) alarm valve  52 . When the pressure of gas provided through conduit  55  is below a selected alarm pressure, the spring within pressure sensing valve  54  forces a piston within valve  54  to exhaust gas from the alarm valve  52  through conduit  56  to conduit  57  and reed alarm  58 . When pressurized gas from the normally open alarm valve  52  is released, the valve  52  opens and further gas is supplied through conduit  53  and conduit  59  to sound the reed alarm  58 . By this means, the operator is given notice when the supplied pressurized gas becomes depleted or obstructed through the means of audible reed alarm  58 . Optionally, a visual pop-indicator  60  supplied via conduit  61  can also be used visually indicate the state of inlet pressure. 
     Although the above description and accompanying drawings relate to a specific preferred embodiment as presently contemplated by the inventors, it will be understood that the invention in its broad aspect includes mechanical and functional equivalents of the elements described and illustrated.