Abstract:
A diaphragm assist device includes a magnetic mat adapted for mounting inside a human body adjacent the diaphragm. The mat is made from a material responsive to application of an electromagnetic field so as to be movable into compressive relation with the diaphragm in response to application of the electromagnetic field thereto and movable out of the compressive relation to permit the diaphragm to relax when application of the electromagnetic field is discontinued. The device also includes an electromagnetic assembly adapted for surrounding the torso of the human body in functionally cooperative relation with respect to the mat, and for alternately generating and discontinuing the electromagnetic field so that the mat alternately moves into and out of the compressive relation with the diaphragm. The device also includes a controller constructed and arranged to control an intensity level of the electromagnetic field generated by the electromagnetic assembly.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of priority from U.S. Provisional Patent Application Ser. Nos. 60/755,413, 60/755,414, 60/755,415, 60/755,416, and 60/755,424, all of which were filed Dec. 31, 2005, the contents of which are incorporated herein by reference in their entireties. The present application is related to U.S. patent application Ser. Nos. 11/648,914, 11/648,635, 11/648,636, and 11/648,637, all of which were filed Jan. 3, 2007, and are incorporated herein by reference in their entireties. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention is generally directed to a device and method for assisting a human diaphragm function. 
     2. Description of Related Art 
     Elevation of the diaphragm may be caused by various dysfunctions of the diaphragm and may interfere with proper functioning of the lungs and heart. For example, when the diaphragm is abnormally elevated, it may compress the lower lobe of the ipsilateral lung, which may then impair proper functioning of the heart, and may ultimately result in the need for mechanical ventilation, or even death. 
     Elevation of the diaphragm may be congenital, and may be caused by eventration of the diaphragm or phrenic nerve palsy. Although phrenic nerve pacing is one technique that may used to improve diaphragmatic function, it may be somewhat limited and may not produce normal function an atrophied diaphragm. 
     Because there is an inherent lack of electrical conductivity in the diaphragm, unlike the heart, placement of multiple surface electrodes on or in the diaphragm typically does not provide uniform contraction of the diaphragm muscle. 
     The potential exists for a large group of patients with diaphragm dysfunction to benefit once further advances in technology can produce smooth coordinated muscular contraction of the diaphragm. 
     BRIEF SUMMARY OF THE INVENTION 
     It is an aspect of the present invention to provide a diaphragmatic assist device to patients suffering from diaphragm dysfunction, as described above. 
     In an embodiment of the present invention, a diaphragm assist device is provided. The device includes a magnetic mat adapted for mounting inside a human body adjacent the diaphragm. The mat is made from a material responsive to application of an electromagnetic field so as to be movable in a first direction into compressive relation with the diaphragm in response to application of the electromagnetic field thereto and movable in a second direction out of the compressive relation to permit the diaphragm to relax when application of the electromagnetic field is discontinued. The device also includes an electromagnetic assembly adapted for mounting on the human body in functionally cooperative relation with respect to the mat, and for alternately generating and discontinuing the electromagnetic field so that the mat alternately moves into and out of the compressive relation with the diaphragm. The electromagnetic assembly is configured to surround the torso of the human body. The device also includes a sensor for evaluating a force applied to the diaphragm during movement of the mat into compressive relation with the diaphragm and for generating an electrical signal as a function of the force, and a controller constructed and arranged to receive the signal generated by the transducer and for controlling an intensity level of the electromagnetic field generated by the electromagnetic assembly as a function of the signal to thereby control a degree to which the mat compresses the diaphragm. 
     In an embodiment of the present invention, a method for assisting diaphragm movement within a human body is provided. The method includes generating an electromagnetic field around the body with an electromagnetic assembly, and moving a magnetic mat disposed adjacent the diaphragm in response to application of the electromagnetic field to the mat in a direction away from lungs within the human body. 
     These and other aspects and advantages of the invention will be apparent from the following description, the accompanying drawings, and the appended claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments of the invention will now be described, by way of example only, with reference to the accompanying schematic drawings in which corresponding reference symbols indicate corresponding parts, and in which: 
         FIG. 1  is a side sectional view of a diaphragm assist device according to an embodiment of the present invention shown inside a human body in a neutral relation with the diaphragm; 
         FIG. 2  is a side sectional view of the diaphragm assist device of  FIG. 1  shown inside the human body in a compressive relation with the diaphragm; 
         FIG. 3  is a side sectional view of the diaphragm assist device of  FIG. 1  shown inside the human body in an expansive relation with the diaphragm; 
         FIG. 4  is a top sectional view of the diaphragm assist device of  FIG. 1  with an electromagnetic assembly of the assist device in a closed and locked position; 
         FIG. 5  is a top sectional view of the diaphragm assist device of  FIG. 4  with the electromagnetic assembly in an open position; and 
         FIG. 6  is a block diagram schematically showing the interrelation of various components of the diaphragm assist device of  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  illustrates a diaphragm assist device according to an embodiment of the invention. In the illustrated embodiment, the device includes a magnetic mat  10  which is adapted to be mounted inside the human body, within the thoracic cavity and adjacent the diaphragm D. Preferably, the mat  10  is a permanent magnet made from a flexible ferro-magnetic material, including but not limited to samarium cobalt, neodymium iron, and neodymium iron boron (NeFeBo). It can be appreciated, however, that the mat may comprise other materials (such as a superconductive material) so long as the mat is sufficiently responsive to application of an electromagnetic field to compress the diaphragm in accordance with the principles of the present invention. Regardless of the material used, however, the exterior surface of the mat should be chemically inert, and not immunogenic, so that it does not react with blood, tissue, or organs. If necessary, the mat may be coated or surrounded by an inert substance, including but not limited to polyvinyl chloride (PVC), polytetrafluoroethylene (PTFE), and zinc. In an embodiment, each magnetic mat has a curvilinear, relatively flat shape and is made from neodymium iron boron (NeFeBo) and has a zinc coating. 
     The mat  10  is supported within the body, preferably in contact with the superior dome of the diaphragm D. If both diaphragms are paralyzed, a magnetic mat may be placed over each diaphragm, as shown in  FIG. 1 . Preferably, the mat support comprises a plurality of heavy mono-filament threads  20  each having one end secured to the mat and another end secured to the rib cage R (or sternum). The threads are flexible to permit movement of the mat, and should be sufficiently strong to withstand continued flexing without breakage. When the mat is disposed on the diaphragm, the threads  20  may also be sutured through the diaphragm so that the mat will stay in position. It can be appreciated that many alternatives to the mono-filament threads can be used to support the mat, as long as such alternatives maintain the mat in movably supported relation proximate to the diaphragm. 
     In an embodiment, the mat  10  may also include, a silicone or silicone-like sleeve  50 , or, alternatively, each magnetic mat may be covered with silicone or a silicone-like substance to decrease the risk of injury to the diaphragm and also to decrease the risk of contact reactivity. Further details of a suitable sleeve may be found in U.S. patent application Ser. No. 11/648,914, which is incorporated herein by reference. The silicone sleeves that cover each mat may be secured loosely to the patient&#39;s ribs and located closely to diaphragmatic tissue. The mat  10  may be placed via thoracoscopy in sections with tongue and groove interlocking joints or hinges. Further details of a magnetic mat that includes sections and hinges may be found in U.S. patent application Ser. No. 11/648,635, which is incorporated herein by reference. The heavy mono-filament threads  20  each have one end thereof secured to the peripheral edges of two opposite sides of the mat, which preferably has a substantially rectangular or oval shape. An incision may be made immediately below the breastbone using the sub-xiphoid approach, and the threads may then be sutured to the rib cage and/or sternum by use of curved trochar sheath. Enough slack should be left in the mono-filament sutures to permit movement of the mat  10  into compressive relation with the diaphragm upon application of an electromagnetic field to the mat  10 , as described in further detail below. 
     An electromagnetic assembly  12  is adapted to be mounted externally to the human body, preferably so that it surrounds the torso T of the body, in functionally cooperative relation with respect to the mat  10 . The electromagnetic assembly  12  includes at least one induction coil  13  that surrounds the torso of the body and to which a current is provided (preferably by a D.C. battery, not shown) to generate or produce an electromagnetic field MF, which moves the mat in a first direction into compressive relation with the diaphragm and away from the lungs L, as shown in  FIG. 2  by arrow F. The operation of the electromagnetic assembly and the magnetic mat may be similar to the electromagnetic assembly and mat disclosed by U.S. Pat. No. 5,498,228, which is incorporated herein by reference in its entirety. 
     More particularly, the electromagnetic assembly  12  may alternately generate and discontinue the electromagnetic field to alternately move the diaphragm and then permit the diaphragm to relax, thereby assisting the mechanical pumping function of the diaphragm. The magnitude of the force produced will be proportionally dependent on the mat&#39;s magnetic field strength, the amount of current traveling through the electromagnetic assembly  12 , and the number of current-turns in the electromagnetic assembly  12 , but inversely proportional to the distance between the electromagnetic assembly and the mat. Optimal coil function may be seen when the coil is adjacent to the torso, with the shortest distance between the ribs and coil. The current in the coil is controlled in time regarding onset and duration, in power regarding quantity of current delivered, and direction as to reverse polarity. 
     For example, the electromagnetic assembly  12  may be configured so that the current that is provided to the coil  13  may be reversed so that a second electromagnetic field MF′ may be applied to the magnetic mat, which causes the magnetic mat to be moved in a second direction that is away from the diaphragm and toward the lungs L, as shown in  FIG. 3  and represented by arrow F′. Because the mat will tend to stick to the diaphragm, the diaphragm will move with the mat  10  via suction. In an embodiment, the mat  10  may be physically attached to the diaphragm D with sutures. When properly timed, such an application and reversal of the electromagnetic field MF may further improve the assistance being provided to the patient, as described in further detail below. 
     As shown in  FIGS. 4 and 5 , the electromagnetic assembly  12  may include a hinge  60  that is configured to allow the electromagnetic assembly  12  to open up like a clamshell. After opening the electromagnetic assembly  12 , the patient would lie in the assembly  12  and the assembly  12  may close and lock with a locking structure  62  so that the coil  13  is a continuous structure wrapped around the torso T. 
     As shown in  FIG. 6 , the diaphragm assist device also includes a transthoracic impedance device (“TID”)  28  that measures transthoracic impedance as the patients breathes. A controller  22  may be programmed with what would be normal transthoracic impedance measurements during inspiration and expiration. As the patient produces, what would be for the patient a normal inspiration, the transthoracic impedance changes, thereby yielding a curve. When inspiration is detected by the device per the curve, current is provided to the coil  13 , which moves the magnetic mat  10  through the coil  13  in a direction as determined by the polarity of the mat and the coil, which is set during manufacture. 
     As the transthoracic impedance device  28  detects expiration, the current provided to the coil  13  may be turned off, or if desired, the current flow may be reversed to that the polarity of the electromagnetic field that is generated by the coil  13  may be reversed to produce opposite movement of the mat  10  and diaphragm. In this manner, both expiration and inspiration may be augmented. 
     The interaction of the coil  13  with the magnetic mat  10  on the diaphragm D will produce a physical force vector both on the diaphragm D and on the coil  13 . Piezoelectric sensors  14  on the electromagnetic assembly  12  may be used to indicate how much force is being applied to the diaphragm D in each direction. This is a feedback mechanism that may be used to avoid excessive force on the diaphragm and potential injury to the diaphragm. 
     As shown in  FIG. 6 , the sensors  14  forms part of an electronic feedback/control loop, and function to evaluate the compressive resistance of the diaphragm during movement of the mat into compressive relation with the diaphragm. The transducer  14  senses the compressive pressure or force applied thereto and outputs a voltage proportional to such force or pressure. The controller  22  receives the signal generated by the transducer and controls the intensity of said electromagnetic field generated by the electromagnetic assembly as a function of that signal. As a result, the controller effectively controls the degree to which the mat moves the diaphragm. 
     More specifically, the controller  22  includes a compensation/comparison circuit  26  (or “compensation circuit”) which compares the voltage generated by the sensors  14  to a command voltage generated by command voltage generator  24 . The command voltage corresponds to a predetermined voltage which represents the ideal amount of force required to move the diaphragm. The compensation/comparison circuit  26  measures the difference between the voltage generated by the sensors  14  and the command voltage, and then digitally compensates for such difference so that an appropriate amount of current is sent through the coil  13  in the electromagnetic assembly  12 . For example, if the voltage generated by sensors  14  is less than the command voltage, the compensation circuit  26  will ramp up the current sent through the coil  13  and thereby increase the intensity of the magnetic field applied by electromagnetic assembly  12 . In contrast, if the voltage generated by sensors  14  is less more than the command voltage, the compensation circuit will decrease the amount of current through the coil  13  and thereby decrease the intensity of the magnetic field applied by the electromagnetic assembly  12 . Thus, the intensity or magnitude of the electromagnetic field generated by the electromagnetic assembly is controlled so that the force applied by the mat  10  to the diaphragm remains within a predetermined range with each compressive stroke. 
     The predetermined amount of force to be applied to the diaphragm in order to obtain the desired output is determined experimentally during an initial procedure wherein a catheter, may placed in the body to monitor pressures in the body near the diaphragm. The pressures are correlated with the voltages generated by the sensors  14 , and after several days of experimentation, the catheter may be removed. The sensors  14  thereafter may generate a voltage as a function of the resistance of the diaphragm. 
     While the magnitude of the electromagnetic field generated by the electromagnetic assembly  12  is controlled by the controller  22 , together with the sensors  14 , it can be appreciated that the frequency of the electromagnetic field will coincide with the natural contractions of the diaphragm. 
     The initial treatment course, which may include a series of treatments may be evaluated regarding the current delivered to the coil and pressure production on the diaphragm. The patient&#39;s resting title volumes, heart rate, oxygen saturation, and respiratory rate may be monitored to determine treatment efficacy. After the initial series, a treatment program may be set up with given currents. Initial treatments may be performed by a fixed device in which the patient may come to a hospital or doctor&#39;s office for initial treatment, and evaluation of the treatment, until a safety protocol has been outlined for that specific patient. Once the patient has safely undergone a series of treatments and current delivery parameters have been established, a portable device may be substituted for home use. 
     It will be appreciated that the aspects of this invention have been fully and effectively accomplished. It will be realized, however, that the foregoing preferred specific embodiments have been shown and described for the purpose of this invention and is subject to change without departure from such principles. Therefore, this invention includes all modifications encompassed within a spirit and scope of the following claims.