Abstract:
Rather than trying to immobilize a living, moving organ to place the organ in the fixed frame of reference of a table-mounted robotic device, the present disclosure teaches mounting a robot in the moving frame of reference of the organ. A miniature crawling robotic device can be introduced, in the case of the heart, into the pericardium through a port, attach itself to the epicardial surface, and then, under the direct control of the surgeon, travel to the desired location for treatment. The problem of beating-heart motion is largely avoided by attaching the device directly to the epicardium. The device can be used for other organs and animals.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     The present application claims priority from U.S. application Ser. No. 10/982,670 filed Nov. 5, 2004 and U.S. provisional application No. 60/518,582 filed Nov. 7, 2003, which are hereby incorporated by reference. 
    
    
     BACKGROUND 
     Heart surgery, particularly the types addressed here (e.g., epicardial electrode placement, atrial ablation) is typically done via either an open approach, or a minimally invasive approach using hand-held rigid endoscopic tools. 
     Several recent development efforts center around robots intended to perform heart surgery, among other procedures. A commercially available robotic system for cardiac surgery is the da Vinci System available from Intuitive Surgical of Mountain View, Calif. That system is teleoperative, meaning that the motions of the surgeon&#39;s hands on input devices are mirrored by laparoscopic manipulators located within the body. While such a system can offer superior dexterity to conventional laparoscopic instruments, it requires some form of stabilization for the heart, requires collapsing a lung, has a limited operative field, and is bulky and expensive. 
     Closed-chest endoscopic visualization of the epicardium was first described by Santos et al. (Arm Thorac Surg 1977; 23:467-470); subsequent reports have utilized the technique for evaluation of blunt chest trauma, pericardial effusion and lung cancer staging. Lattouf et al have utilized the technique for epicardial implantation of left ventricular pacing leads. In each of these reports, endoscope access required thoracotomy with breach of the left pleural space. Direct access to the pericardial space via subxiphoid puncture is an increasingly practiced technique during catheter ablation procedures. In these reports, once access was achieved, catheter manipulation was guided solely by fluoroscopy. We are aware of cursory attempts at standard pacing lead implantation using this approach which have failed due to inability to achieve fixation. 
     The challenges of minimally invasive access are further complicated by the goal of avoiding cardiopulmonary bypass, and this goal necessitates surgery on a beating heart. Thus instrumentation is needed that allows stable manipulation of an arbitrary location on the epicardium while the heart is beating. See, for example, published application number 20040172033. Local immobilization of the heart is the approach generally followed with endoscopic stabilizers such as the Endostab device and the endo-Octopus device, which operate with pressure or suction. However, the resulting forces exerted on the myocardium can cause changes in the electrophysiological and hemodynamic performance of the heart, and there has been discussion in the literature regarding the care that must be taken to avoid hemodynamic impairment [Falk, et al., Endoscopic coronary artery bypass grafting on the beating heart using a computer enhanced telemanipulation system. Heart Surg Forum 2:199-205, 1999]. As an alternative, several researchers in robot-assisted endoscopic surgery are investigating active compensation of heartbeat motion by visually tracking the epicardium and moving the tool tips accordingly [           avu         o{hacek over (g)}lu M C, et al., Robotics for telesurgery: second generation Berkeley/UCSF laparoscopic telesurgical workstation and looking towards the future applications. Industrial Robot 30:22-29, 2003; Ortmaier T J. Motion compensation in minimally invasive robotic surgery. Ph.D. dissertation, Technical University of Munich, Germany, 2003.], but this research problem remains open. The motion of the beating heart is complex. In addition to the challenges of modeling or tracking the heart surface, active compensation will require considerable expense for high-bandwidth actuation to enable manipulation in at least three degrees of freedom over a relatively large workspace (See Cavusoglu, supra).
     BRIEF SUMMARY 
     The prior art solutions address a problem that exists only because the tools are held by a surgeon or a robot that is fixed to the table or standing on the floor. The present disclosure takes a different approach. Rather than trying to immobilize the heart surface to stabilize it in the fixed frame of reference of a table-mounted robotic device, we mounted the device in the moving reference frame of the beating heart. That task was accomplished with a miniature crawling robotic device designed to be introduced into the pericardium through a port, attach itself to the epicardial surface, and then, under the direct control of the surgeon, travel to the desired location for treatment. The problem of beating-heart motion was largely avoided by attaching the device directly to the epicardium. The problem of access was resolved by incorporating the capability for locomotion. 
     Improved access and precise manipulation are not the only benefits of this approach. Port access for minimally invasive cardiac surgery has typically been transthoracic, largely to accommodate the rigid endoscopes generally used for both manual and robot-assisted procedures. Transthoracic access to the heart requires deflation of the left lung, general endotracheal anesthesia, and differential lung ventilation. A variety of current and upcoming procedures, however, can conceivably be performed transpericardially, without invasion of the pleural space, with appropriate instrumentation. Examples include, but are not limited to cell transplantation, gene therapy for angiogenesis, epicardial electrode placement for resynchronization, epicardial atrial ablation, intrapericardial drug delivery, and ventricle-to-coronary artery bypass, among others. 
     The ability of the device to move to any desired location on the epicardium from any starting point enables minimally invasive cardiac surgery to become independent of the location of the pericardial incision. Use of the device also allows a subxiphoid transpericardial approach to any intrapericardial procedure, regardless of the location of the treatment site. As a result, deflation of the left lung is no longer needed, and it becomes feasible to use local or regional rather than general anesthetic techniques. These advantages have the potential for opening the way to ambulatory outpatient cardiac surgery. The opportunity for “synergy” (e.g. multiple procedures during a single operative session) may prove particularly valuable. The techniques disclosed herein are applicable to other organs within a living body and need not be limited to the human heart, which is merely our first application. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For the present disclosure to be easily understood and readily practiced, the present disclosure will now be described, for purposes of illustration and not limitation, in connection with the following figures wherein: 
         FIG. 1  is a forward isometric view of the distal body and proximal body which, together with the control wires and suction lines, makeup one embodiment of the robot; 
         FIG. 2  is a rearward isometric view of the distal and proximal bodies of  FIG. 1 ; 
         FIGS. 3A-3D  illustrate forward locomotion of the robot; 
         FIGS. 4A-4C  illustrate side to side turns of the robot; 
         FIG. 5A  illustrates another embodiment of a robot and control system according to the present disclosure while  FIG. 5B  illustrates a washer-like support spacer; 
         FIG. 6A  is an example of one type of end effector, a semicircular needle, retracted into a recessed storage location in the distal body while  FIG. 6B  illustrates the needle in operation; 
         FIGS. 7A and 7B  are an example of another type of end effector; 
         FIG. 8  illustrates a self contained embodiment of the device of the present disclosure; 
         FIGS. 9A and 9B  illustrate one example of a streamlined device of the present disclosure; 
         FIGS. 10A and 10B  illustrate another example of a streamlined device of the present disclosure; 
         FIGS. 11A and 11B  illustrate an embodiment of a device of the present disclosure having stabilization struts; and 
         FIG. 12  is a conceptual illustration of the robot maneuvering on the surface of a heart to perform a procedure. 
     
    
    
     DETAILED DESCRIPTION 
     One embodiment of a robot constructed according to the present disclosure is illustrated in  FIGS. 1 and 2 .  FIGS. 1 and 2  illustrate a prototype device  10  designed and constructed in the Medical Instrumentation Lab at Carnegie Mellon University, which will now be described for purposes of illustration and not limitation. The device  10  consists of two glass-filled polycarbonate shells forming a distal body  12  and a proximal body  14 , each body having a 13 mm circular footprint and a height of 14 mm. That size allows the device  10  to fit within a standard 20 mm diameter cannula or port. Each of the body sections  12 ,  14  is equipped with an independent suction line  16 ,  18  and suction pad  20 ,  22 , respectively, for gripping to biological tissue. The suction lines  16 ,  18  and suction pads  20 ,  22  illustrate one type of means for prehension. 
     The translation and rotation of the body sections  12 ,  14  relative to one another are controlled from an external control system, in this embodiment a handle  15  (shown in  FIGS. 3A-3D  and  FIGS. 4A-4C ), by manually adjusting the lengths of three nitinol wires  24 ,  25 ,  26  running along the longitudinal axis of the device  10 . The super-elasticity of nitinol allows the wires to support tension and compression (i.e. pulling and pushing) without permanently deforming. That eliminates the need for shape restoring components (like springs) that are required in some other systems. The axes of these wires  24 ,  25 ,  26  intersect the body sections  12 ,  14  at the perimeter of a 10 mm diameter circle at 120-degree intervals. The wires  24 ,  25 ,  26  are fixed to the distal body  12  and pass freely through the proximal body  14  out to the handle  15  of the device. Between the proximal body  14  and the handle  15 , the wires  24 ,  25 ,  26  are contained within sheathes  24 ′,  25 ′,  26 ′, respectively, e.g. flexible plastic tubing, whose ends are attached to the proximal body  14  and the handle  15 . The three independently actuated wires  24 ,  25 ,  26  provide three degrees of freedom between the distal body  12  and the proximal body  14 , two angular and one tanslational. The two angular degrees of freedom allow the device  10  to adapt to the curvature of the heart (or other organ) as well as turn laterally (i.e. yaw). 
     The sheaths  24 ′,  25 ′,  26 ′ prevent bowing of the wires  24 ,  25 ,  26  so as to transmit the forces applied to the wires  24 ,  25 ,  26 , respectively, at the handle  15  to either proximal body  14  or distal body  12  and ensure that the length of wires  24 ,  25 ,  26  between the handle  15  and proximal body  14  remains constant. Thus, when the length of a wire exiting its sheath at the handle is changed, the length of that wire between the proximal body  14  and the distal body  12  changes by the same amount. 
     Inchworm-like locomotion is achieved by alternating the suction force exerted by the two body sections, while changing the lengths of the wires at the fixed handle, as shown in  FIGS. 3A-3D . The configuration of the sheaths  24 ′,  25 ′  26 ′ and enclosed wires  24 .  25 ,  26  does not affect the locomotion of the device  10  as long as there is slack between the handle  15  and the proximal body  14 , some of which will be taken up with each forward step. In the figure, the heavy black line indicates which suction pad is active. Note that the configuration of the sheaths and enclosed wires between the handle  15  and proximal body  14  changes with each forward step, but the lengths remain constant. 
     Between  FIGS. 3A and 3B , while the proximal suction pad  22  is turned on, the wires  24 ,  25 ,  26  are moved forward causing distal body  12  to move forward by the same amount. In  FIG. 3C , the proximal suction pad  22  is turned off and the distal suction pad  20  is turned on. In  FIG. 3D , the compression in the sheaths  24 ′,  25 ′,  26 ′ is released, causing the proximal body  14  to “catch up” with the distal body  12 . Another forward step can now be taken by repeating the process. Turning can be achieved by differentially changing the lengths of the side wires as shown in  FIGS. 4A-4C . The actuation of the wires at the handle may be performed manually, along with the opening and closing of the valves to the suction lines. 
     Another embodiment is illustrated in  FIG. 5 . In  FIG. 5 , components having similar functions and construction to those of  FIGS. 1 and 2  have like reference numbers. The embodiment of  FIG. 5  differs from the previous embodiment in several ways. For example, between the proximal body  14  and distal body  12  the wires  24 ,  25 ,  26  may be attached to a support spring  27  by eyelets  28  to prevent the wires  24 ,  25 ,  26  from bowing during turning and to ensure that the wires maintain an equal distance from one another. The support spring  27  may have a very low spring constant (e.g. k=0.012 N/mm) such that the restoring force is negligible as compared to that of the wires  24 ,  25 ,  26 . As an alternative to the spring  27  and eyelets  28 , a plurality of flat, washer-like structures  31  (See  FIG. 5B ) may be provided to maintain the proper spacing between wires  24 ,  25 ,  26 . The plurality of washer-like structures  31  may be separated from one another by springs (not shown). 
     A 1.6 mm diameter commercial fiberscope  29 , running longitudinally through the length of the device, may be fixed on the distal body  12  to provide visual feedback, with or without the use of an adjustable mirror  40 . The images from the fiberscope  29  may be captured with a digital video camera  42  and displayed as a part of the graphical user interface (GUI)  44 , both of which are part of a control system  46 . The control system  46  may include sensors  48  for monitoring the vacuum supplied by suction lines  16 ,  18 , electronically controlled valves  50  for determining which suction pad  20 ,  22  is operative, and vacuum source  52 . The control system  46  may also include motors  54  for controlling movement of wires  24 ,  25   26 . A computer  55  may be provided to control the various components in response to information input by the surgeon via the GUI  44  to control locomotion and other functions. Such a design allows for the motors  54 , solenoid valves  50 , etc. to be located outside the device  10 . It is anticipated that the robot  10  may be either a disposable device or a reusable, sterilizable device. 
     In the embodiment of  FIG. 5 , the suction pads  20 ,  22  are connected to the bodies  12 ,  14  by means of flexible feet  56 ,  58 , respectively. That enables the suction pads  20 ,  22  more freedom to conform to the surface of the organ. Meshes (not shown) may cover the bottom of the suction pads to keep out large particles, while suction filters  60  may be provided to remove fluids and small particles. 
     An aspect of the present invention is changing the frame of reference of the robot from that of the surgeon to that of the moving organ. The exact form and construction of the robot used to bring about that change of reference is not critical to this aspect of the invention. For example, although in the disclosed embodiments locomotion is achieved through the advancement of wires, either manually or through the activation of motors, others means of locomotion may be provided such as local (i.e. positioned on the robot) electric motors (operated with or without a tether), local ultrasonic motors (operated with or without a tether), as well as pneumatic actuators (typically operated with a tether). The means for prehension in the disclosed embodiment is suction. Alternative means of prehension may include synthetic gecko foot hair [Sitti M, Fearing R S (2003) Synthetic gecko foot-hair micro/nano-structures as dry adhesives. J Adhesion Sci Technol 17(8):1055-1073] or a “tacky” foot. The actuation for treatment may include all the same alternatives as for locomotion. Finally, the device may operate with a tether having wires and pneumatic lines as disclosed above, with a tether having electric wires for local motors or video from a camera, or the device may operate without a tether. Tetherless models could be powered by a battery, the transcutaneous charging of a coil, etc., and could be controlled by local computing or through radio frequency transmissions. It will be understood by those of ordinary skill in the art that changing the frame of reference of the robot from that of the surgeon to that of the moving organ can be brought about by a wide variety of robots designed so as to be able to move within a loosely bounded body cavity. A loosely bounded body cavity refers to that space surrounding an organ such as, for example, the peritoneal space surrounding the liver, the pleural space surrounding the lungs, the pericardial space surrounding the heart, etc., in addition to the space within certain organs such as the heart or stomach. 
       FIG. 6A  illustrates an end effector (tool), which in this example is a needle  30  carried within a recess  32  in distal body  12 . Distal body  12  also carries a means for providing images such as a fiberscope or camera, with or without some combination of lenses, mirrors, fiberoptics, etc. The needle  30  may be used to perform epicardial electrode lead placement for cardiac resynchronization therapy (CRT) via subxiphoid videopericardioscopic access. A robot  10  equipped with the needle  30  can perform a minimally invasive suturing technique that can be used with a variety of epicardial pacing leads, both permanent and temporary. 
     Needle  30  is a high-strength needle for suturing that has a drive shaft (not shown) that runs along the long axis of the device  10 , entered laterally and located below the midline of distal body  12 . At the distal (working) end of this drive shaft is the needle  30  which is a segment (roughly 5 mm) that is bent 90° with respect to the drive shaft, forming the radius of a circle. The needle  30  will then terminate in a semicircular suturing portion. The lower half of the front end of the distal body  12  has a semicircular channel  32  into which the needle  30  recedes when it is not in use, protecting both the cardiac tissue and the needle  30 . 
     The proximal end of the suture thread  36  remains outside the body. The distal end of the thread  36  is connected to a sharpened cap  38 , which will fit snugly over the end of the needle  30 . When the surgeon has positioned the distal body  12  at a desired work site, suturing will be performed by advancing the needle  30  from its recessed storage channel  32  (see  FIG. 5B ) and then rotating the drive shaft, forcing the semicircular needle  30  and the sharpened cap  38  with its suture thread  36  to pass through the tissue in an arc and exit again with the suture cap  38  still on the tip of the needle  30 . A minimally invasive forceps (not shown), passing through an off-center working port of the robot  10  will be used to grasp the thread  36 , lift the thread  36  and its cap  38  from the tip of the needle  30 , and retract the cap  38  and distal end of the thread  36  all the way back through the cannula to the outside of the body. Here, the surgeon will knot the suture with his own hands, tying a single throw (or half of a square knot) in the thread. Once the single throw has been tied, the surgeon will place a wire with a slightly forked tip against the knot, with the knot resting in the notch of the fork, and will use the wire to push the knot all the way back against the epicardium. He will then tie a second throw and use the wire to push it forward until it meets the first throw, completing the knot. Given an ample supply of sutures fitted with sharpened caps, this technique can be repeated as many times as necessary, by placing each sharpened cap on the tip of the needle using the same forceps that is used to retrieve it from the needle. 
     The robot  10  will have a separate electrode channel that will allow passage of the electrode and its wire lead from outside the body into the pericardium to be sutured to the heart. The needle  30 , forceps, wire “fork”, suture with sharpened cap, and all supporting instrumentation needed for the suturing technique may be designed for sterilizability. Actuation from outside the body is the most feasible option for the forceps, because the forceps must be fully retractable to bring the tip of the suture thread back to the hand of the surgeon. Actuation of the needle for suturing may be performed locally by motors inside the robot, or from outside the body using a wire running through the cannula. Visual feedback for suturing may be provided by the same device used during locomotion. 
     Another end effector (tool) is illustrated in  FIGS. 7A and 7B . Like components carry the same reference numbers as used in the previous figures. In the device of  FIGS. 7A and 7B , the washer-like structure  31  and spacer springs have been eliminated for purposes of clarity. The reader will understand that a plurality of washer-like structures  31  and spacer springs may be used in the embodiment of  FIGS. 7A and 7B . An experiment using this end effector, needle  70 , was performed on a pig. Through a 15 mm pericardial opening at the junction between the pericardium and the diaphragm at the midline, the device  10  was manually introduced inside the intact pericardium. Suction was applied to both suction pads. Stable contact with the epicardium of the beating anterior wall of the right ventricle was visually confirmed for a period of 30 seconds. The device  10  was then advanced across the left anterior descending coronary artery over the anterior wall of the beating left ventricle. Consistent stable contract with the epicardium of the beating left ventricle was observed. The device  10  was then further advanced over the left atrial appendage and stable fixation to the surface of the beating left atrium was confirmed. 
     Successful locomotion of the device  10  inside the intact pericardium was confirmed on the following areas: anterior wall of the beating right ventricle, anterolateral wall of the beating left ventricle, and anterior wall of the left atrial appendage. No gross epicardial or pericardial damage was observed. Because the present prototype has no outer shell between the bodies  12 ,  14 , nothing prevented the pericardium from hanging down one or two millimeters between the bodies, and the leading edge of the proximal body  12 , which was not tapered, then tended to snag somewhat on the pericardium. The pericardial sac also showed a tendency to adhere to all surfaces of the device  10  that it contacted, no matter how smooth. This seemed to be largely caused by drying of the sac due to exposure to air. Occasional infusions of normal saline solution were used for lubrication, which succeeded in alleviating the problem. 
     Two myocardial injections of tissue-marking dye were performed during the experiment. In each case, the device  10  walked to the desired site, locked down both bodies using suction, and then the surgeon performed the injection manually by advancing the 27G custom needle  70  through a working port. For the first injection, the device  10  was positioned over the bifurcation of the left anterior descending coronary artery and the takeoff of the diagonal branch; the needle  70  was advanced into the left ventricular myocardium for 2-3 mm and 0.5 cc of dye was injected. The maximum force applied during injection was 0.72 N. The device  10  was then moved over the diagonal coronary artery and another injection of 0.5 cc of dye was made over the anterolateral wall of the left ventricle. The maximum force applied to the needle during the second injection was 1.15 N. No bleeding was observed after the needle  70  was withdrawn. Confirmation of successful injection was made at postoperative examination. 
     Because the device is tethered, pulling the tether provided a feasible method in the preliminary experiments to apply a tangential force to dislodge the device, without requiring the development of additional hardware that could be inserted somehow into the pericardial sac for testing. The force necessary to dislodge the device from the epicardium by pulling on the tether was measured with a force gauge while the device held onto the heart. A small clamp was applied to the part of the tether consisting of the three drive wires and their sheaths, and this clamp was attached to a handheld digital force gauge. The surgeon then pulled on the force gauge until the device was dislodged, and the gauge recorded the maximum force encountered during each trial. This test was performed three times with suction applied only to the distal body, three times with suction applied only to the proximal body, and three times with suction applied to both bodies. The results are presented in Table 1. No damage to the device resulted from these tests. 
     
       
         
               
               
               
               
               
             
           
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 Body with 
                 Number of 
                   
                 Standard 
               
               
                   
                 suction applied 
                 trials 
                 Mean (N) 
                 deviation (N) 
               
               
                   
                   
               
             
             
               
                   
                 distal 
                 3 
                 1.62 
                 0.37 
               
               
                   
                 proximal 
                 3 
                 3.23 
                 0.70 
               
               
                   
                 both 
                 3 
                 4.48 
                 0.43 
               
               
                   
                   
               
             
          
         
       
     
     During this experiment we demonstrated a technique for reattachment that can be used if the device is accidentally detached from the epicardium. This test was performed while the device was inside the intact pericardium. In this test, all suction was turned off, and, by manually twisting the tether, the device was intentionally rotated and was left lying on its right side on the epicardium. The suction in both pads  20 ,  22  was then turned on. By manually twisting the tether with a counterclockwise motion, the device was righted so that once again it correctly grasped the epicardial surface using the suction, and remained attached as before. The first time this test was performed, a video device was used to view the device  10 , and by its presence lifted the pericardium somewhat, so that it did not lie as low on and around the device  10  as it normally would. Therefore, to avoid this effect, the video device was removed from the pericardium, and the test was repeated, this time with only the external video recorder monitoring the trial. Righting and reattaching of the device was performed successfully in both trials with no tissue damage and no damage to the device. 
     The ease with which the device can be retrieved from the pericardium was tested by measuring the maximum force encountered during extraction. The device was positioned normally inside the pericardium, standing upright on its feet with the distal body of the device near the left atrium, roughly 10 cm from the entry incision. All suction was turned off. The device was then retracted completely from the pericardium by pulling on the tether. This test was repeated three times, and the peak force measured during retrieval was recorded during each trial. The mean peak force measured was 2.49±0.51 N. 
       FIG. 8  illustrates a self-contained design of the device  10 , with the proximal body  14  shown at the upper left of the figure and the distal body  12  at the lower right. This design involves two motors for locomotion. One motor would be located in the vertical cylindrical body of the proximal body  14  and the other motor located in the horizontal cylinder  74  visible in the arm connecting the proximal  14  and distal  12  bodies. For clarity, a streamline housing, discussed below, is not shown in  FIG. 8 . The motors could receive power and instructions through a tether (not shown) or from an onboard battery and an onboard computer (not shown). 
       FIGS. 9A and 9B  illustrate a device  10  with a capsular or pill-like design for streamline interaction with the pericardial sac. The device  10  has a two piece hard covering, one piece of which slides inside the other like a gelatin capsule of the sort often used for pills.  FIG. 9A  illustrates the device  10  in an extended phase of a step, i.e. maximum distance between the distal body  12  and proximal body  14 , while  FIG. 9B  illustrates the contracted phase of the step, i.e. minimal distance between the proximal body  14  and distal body  12 . 
       FIGS. 10A and 10B  illustrate another design of the device  10  with a one-piece outer shell designed for streamline interaction with the pericardial sac. This design may be used in place of the design of  FIGS. 9A and 9B  should that design be found to cause pinching of the pericardium during locomotion.  FIG. 10A  illustrates the extended phase of a step while  FIG. 10B  illustrates the contracted phase of the step. 
       FIGS. 11A and 11B  illustrate a design in which deployable outrigger-like struts  80 ,  82  are used if stronger safeguards against tipping become necessary. The outrigger-like struts  80 ,  82  would be foldable from the horizontal positions shown to vertical positions adjacent distal body  12  on both sides of the device  10 . Once the device  10  is deployed within the pericardium, the struts  80 ,  82  may be moved from the horizontal to the vertical position shown in the figures to guard against tipping. If the struts  80 ,  82  evidence any tendency to snag the pericardium, a stretchable membrane  84  may be employed to cover both the device  10  and the struts  80 ,  82  as shown in the figures.  FIG. 11A  illustrates the extended phase of a step while  FIG. 11B  illustrates the contracted phase of the step. 
     Turning to  FIG. 12 , in operation according to one aspect of the present invention, the device  10  will enter the pericardium and be placed on the epicardial surface of the heart using a rigid or flexible endoscope with a working port. The endoscope will be introduced into the pericardial sac through a port or limited incision beneath the xiphoid process of the sternum. 
     Once positioned appropriately with the endoscope under direct visual confirmation, the device  10  will grasp the epicardium using suction. The suction forces are applied through the two independent suction pads  20 ,  22  (see  FIG. 5 ) that may be attached directly to bodies  12 ,  14  or through compliant or flexible feet  56 ,  58 , respectively. The vacuum pressure is supplied to the suction pads  20 ,  22  by the vacuum source  52  through the operation of valves  50  and suction lines  16 ,  18  respectively. The vacuum source provides a vacuum pressure of −0.08 N/mm 2 , which was found to be effective and safe for use in FDA approved cardiac stabilizers. The suction forces generated by this pressure have proven effective for our application, and did not damage the epicardial tissue. During locomotion, the vacuum pressure is monitored by the external pressure sensors  48  and regulated by computer-controlled solenoid valves  50 , both located within the control system  46 . Based on this pressure, the normal and tangential forces calculated to dislodge one of the bodies  12 ,  14  are 1.76 N and 0.87 N, respectively. Bench testing using a force gauge to dislodge the device from a poultry model verified normal and tangential forces of 2.01 N and 0.86 N. The tangential force that can be resisted by the device will be increased significantly by reducing the profile. 
     The device  10  will provide visual feedback to the surgeon during locomotion and administration of therapy. That can be accomplished using fiberoptics to relay the image from the distal end  12  of the device  10  to the camera  42  located in the control system  46 . Alternatively, a CCD video camera can be mounted directly to the distal end  12  of the device  10 . It may be possible to provide all of the necessary vision with a single visual sensor on a fixed mount. More likely, however, either the viewing head will be actuated for motion, or two imaging devices will be incorporated: one tangential to the surface of the organ (looking forward) for providing information for navigation, and the other normal to the surface (looking down) for providing a view of the area to receive attention. “Attention” is intended to be a broad term that includes all types of interventions in addition to all forms of testing, viewing or inspecting a site, etc., or any other activity that results in consideration being devoted to an organ or a portion of an organ. 
     The device  10  differs from prior art robotic surgical systems in several fundamental ways: (1) it operates within the reference frame of the heart rather than that of an operating table, (2) it will be introduced using a sub-xiphoid rather than an intercostal approach, obviating general endotracheal anesthesia (GETA), (3) it has locomotive capabilities, and (4) it will be relatively inexpensive and possibly disposable. For surgical procedures that can be performed completely within the pericardium, the device  10  will eliminate many of the limitations of these surgical systems. 
     Therapies administered from the device  10  will not require stabilization of the heart because the device  10  will be located in the same reference frame as the surface of the heart, rather than that of a fixed operating table. This eliminates the need for either endoscopic stabilizers, which require additional incisions, or cardiopulmonary bypass, which increases the complexity and risk of the procedure. 
     The teleoperative surgical systems in use today utilize laparoscopic manipulators and cameras and are introduced to the pericardial sac through several intercostal (between rib) incisions. These instruments must then pass through the pleural space before reaching the heart, which requires the collapsing of a lung. The delivery of the device  10  onto the heart will not require collapsing a lung because it will be introduced to the thoracic cavity through an incision made directly below the xiphoid process. The endoscope will then be pushed through the tissue and fascia beneath the sternum until the bare area of the pericardium is reached, never entering the pleural space. The scope will also be used to breach the pericardium, thus delivering the device  10  directly to the epicardium. Because the device  10  will not require the collapsing of a lung, it will also not require differential ventilation of the patient, and it is therefore possible that local or regional anesthesia could be used instead of general endotracheal anesthesia (GETA). As a result, a potential benefit is that the device  10  may enable certain cardiovascular interventions to be performed on an ambulatory outpatient basis, something that has never been done before. 
     The locomotive capabilities of the device  10  will enable it to reach virtually any position and orientation on the epicardium. This is not the case with rigid laparoscopes, which are limited to a relatively small workspace near the entry incision. In addition, these systems require the removal and re-insertion of the tools to change the operative field within a single procedure. The device  10 , on the other hand, can easily change its workspace by simply moving to another region of the heart. 
     The da Vinci surgical system is very expensive and consists of a surgeon&#39;s computerized console and a patient-side cart with multiple large robotic arms. For procedures that can be performed within the pericardium, the device  10  will provide a small, extremely low-cost alternative to this system. 
     With proper development of end-effectors, the TEM will be able to perform epicardial cardiac procedures such as: cell transplantation, gene therapy, atrial ablation, and electrode placement for resynchronization myocardial revascularization. Devices such as an ultrasound transducer, diagnostic aid or other sensor, drug delivery system, therapeutic device, optical fiber, camera or surgical tool(s) may be carried by the device  10 . 
     Procedures for organs other than the heart can be developed while remaining within the teachings of the present disclosure. Additionally, procedures on living bodies other than humans, e.g. pets, farm animals, race horses, etc. can be developed while remaining within the teachings of the present disclosure. Thus, while the present invention has been described in connection with preferred embodiments thereof, those of ordinary skill in the art will recognize that many modifications and variations are possible. The present invention is intended to be limited only by the following claims and not by the foregoing description which is intended to set forth the presently preferred embodiment.