Abstract: A method of determining the voltage and current output required for the application of specific and selective electric and electromagnetic signals to diseased articular cartilage in the treatment of osteoarthritis, cartilage defects due to trauma or sports injury, or used as an adjunct with other therapies (cell transplantation, tissue-engineered scaffolds, growth factors, etc.) for treating cartilage defects in the human knee joint and a device for delivering such signals to a patient's knee. An analytical model of the human knee is developed whereby the total tissue volume in the human knee may be determined for comparison to the total tissue volume of the diseased tissue in the animal model using electric field and current density histograms.

Abstract: A stimulator and a method for electrical stimulation of bone to promote osteogenesis is disclosed in which surface electrodes positioned around an incision site transmit an interferential current that has a base medium frequency alternating current between 1K-20 KHz. A digital signal processor generates a sine-wave-like waveform from a pulse generator which after further processing is used to generate two circuits for use in producing the interferential current. The effective area of stimulation is controlled by placement of electrodes and electrode orientation. Amplitude modulation of electrical circuits created at the electrode placements also augments the effective area of stimulation.

Abstract: A method for providing electromagnetic therapy to a patient includes placing the patient in proximity to an electromagnetic therapy apparatus. The electromagnetic therapy apparatus includes an electrical circuit for generating an electrical drive signal, a first transducer coil and a second transducer coil for generating respective electromagnetic fields in response to the drive signal, a first portion with a configuration corresponding generally with a chair seat, and a second portion with a configuration corresponding generally with a chair back. The first transducer coil is disposed within the first portion and the second transducer coil is disposed within the second portion. The method further includes stimulating the patient with a pulsed electromagnetic field from at least the first and second transducer coils. The pulsed electromagnetic field having a number of pulses, each pulse having a pulse period of ten microseconds to twenty microseconds.

Abstract: A method and device is disclosed for inhibiting bone growth, including inducing epiphysiodesis or hemiepiphysiodesis, using electrical current. The device includes a power source and one or a series of electrodes for applying a current sufficient to reduce or stop the growth of a bone to selected regions of the bone. The method and device may be used to correct growth discrepancies in extremities such as the arms or legs, as well as correct the curvature of the spine in scoliosis patients.

Abstract: Bone screw (10a) having a hollow, tubular shaft (12a) consisting of metal, such as titanium, the shaft having a head (14a) at one end and a self-tapping external thread (18a) at the other end. The head (14a) has a hexagonal recess (16a) for inserting a turning tool. An electrically insulated metallic end-piece (20a) which tapers in the direction of the end in the form of a cone or pointed arch, is inserted the other end of the shaft (12a). A receiving coil (30a) is located in the hollow shaft (12a), the terminals (36a, 38a) of the coil being electrically coupled to the shaft (12a) and to the end-piece (20a). The space between the end-piece (20a) and the end of the shaft (12a) as well as the interior of the shaft (12a) are filled with a biocompatible insulating compound (26a), such as an epoxy resin. A low-frequency electric voltage can be induced in the receiving coil by an external primary coil which is coupled to an oscillation generator.

Abstract: An electrosurgical medical device and method for creating thermal welds in engaged tissue. In one embodiment, at least one jaw of the instrument defines a tissue engagement plane that carries a recessed central portion. In another embodiment, the controller coupled to the Rf source is adapted to switch from a power control operational mode to a voltage controlled operational mode at a selected transition impedance level.

Abstract: Pathological conditions are alleviated by bone conduction practiced by the application of sinusoidal electric waves at frequencies of between 4,200 and 6,500 hertz at less than 200 microamperes current.

Abstract: A multi-functional portable electro-medical device provides interferential current stimulation to promote bone growth. Two electrical signals are applied to a target area, each electrical signal being formed by a set of two electrode pads. A beat frequency is created at the location the signals intersect with each other. The beat frequency is the difference between the frequencies of the two signals and has an amplitude that is additive and greater than either signal alone. The depth of the interferential signal is increased by increasing the carrier frequency of the signals. The direction of the interferential signal shifts toward the signal having the lower amplitude. The electrical stimulation is used in combination with biologics to further increase bone growth.

Abstract: A combined tissue/bone growth stimulator and external fixation device is provided to aid in the treatment of fractures, osteotomies, soft tissue injuries, and reconstructive surgery and to reduce the likelihood of complications. The tissue/bone growth stimulator apparatus includes an external fixation device for stabilization of a selected portion of a patient. The tissue/bone growth stimulator apparatus also includes an electrical circuit attached to and forming an integral component of the external fixation device and operable to generate an electrical drive signal. The tissue/bone growth stimulator apparatus also includes a cable adapted to connect the electrical drive signal to a stimulator portion operable to provide an electromagnetic field to stimulate the growth of bone and tissue at the selected portion of the patient and/or at other portions of the patient. More particularly, the electromagnetic field may be produced by directing a current through the external fixation device into the patient.

Abstract: A multi-functional portable electro-medical device provides interferential current stimulation to promote bone growth. Two electrical signals are applied to a target area, each electrical signal being formed by a set of two electrode pads. A beat frequency is created at the location the signals intersect with each other. The beat frequency is the difference between the frequencies of the two signals and has an amplitude that is additive and greater than either signal alone. The depth of the interferential signal is increased by increasing the carrier frequency of the signals. The direction of the interferential signal shifts toward the signal having the lower amplitude. The electrical stimulation is used in combination with biologics to further increase bone growth. The target area is large enough to include multiple vertebral segments.

Abstract: An implantable composition of a biocompatible porous metal for enhanced tissue in-growth and fixation in the body. The metal has a porosity greater than 80% and up to about 95% which allows good cell population, yet it also provides structural integrity and stability allowing its use as a weight-bearing implant. In various embodiments, the metal may be titanium, which includes titanium alloys, or may be a cobalt-chromium-molybdenum alloy. The high porosity desirably facilitates in-growth of cells and/or tissues, which in turn facilitates biological fixation and biocompatibility. This is beneficial, for example, in an orthopedic implant such as a hip replacement, for facilitating in-growth of connective tissue and bone cells. The porous composition is structurally stable.

Abstract: An implantable neurological stimulation system has an in-growth anchor coupleable to an implantable stimulation lead that configured for anchoring the stimulation lead to tissue. The stimulation lead is coupled to an implantable neurostimulator, and the in-growth anchor is positioned proximal to at least one electrode. Many embodiments of the implantable neurological stimulation system with in-growth anchor and its methods of operation are possible.

Abstract: A method and apparatus for preparing a bone product are provided. The method includes contacting an interior section of a cylindrical bone portion with a high pressure fluid medium such as at least about 1000 psi to remove at least a portion of cancellous bone matrix from the bone portion. Preferably the bone contains less than about 25% by weight cancellous bone. The apparatus includes multiple stations of opposing high pressure nozzles holding the cylindrical bone portion from each end and for contacting the interior surfaces of a bone portion with a fluid medium. The apparatus also includes a third nozzle for contacting the exterior surface of the bone portion with a fluid medium.

Abstract: The present invention is a device that allows electrical stimulation to an anatomical site that is covered by a cast. The electrode is applied to achieve a desired physiological response (e.g., bone growth), treatment of pain, or the prevention of muscle atrophy.

Abstract: An electrical bone growth promotion apparatus and method for the delivery of electrical current to an implant surgically implanted within the intervertebral space between two adjacent vertebrae of the spine to promote bone growth and the fusion process to areas adjacent to the implant is disclosed. The apparatus of the present invention comprises a self contained implant having a surgically implantable, renewable power supply and related control circuitry for delivering electrical current directly to the implant and thus directly to the area in which the promotion of bone growth is desired. The desired areas of bone growth promotion may be controlled by conducting negative charge only to the desired location of bone growth promotion.

Abstract: A multi-functional portable electro-medical device provides interferential current stimulation to promote bone growth. Two electrical signals are applied to a target area, each electrical signal being formed by a set of two electrode pads. A beat frequency is created at the location the signals intersect with each other. The beat frequency is the difference between the frequencies of the two signals and has an amplitude that is additive and greater than either signal alone. The depth of the interferential signal is increased by increasing the carrier frequency of the signals. The direction of the interferential signal shifts toward the signal having the lower amplitude. The electrical stimulation is used in combination with biologics to further increase bone growth.

Abstract: A method of fusing or welding bone in vivo and in a fluid medium, comprising: harvesting a piece of autologous implant bone; treating the implant bone and/or a receiving bone to expose organic component; treating the implant bone and/or the receiving bone by de-fatting; combining the implant bone with other compounds to create an interfacing agent; adding the interfacing agent between receiving bone segments to be fused or welded; and fusing or welding in vivo, in a fluid medium, utilizing electromagnetic energy.

Abstract: An apparatus for generating an electrical signal for use in biomedical applications, including two timing blocks for generating timing intervals T1-T7, an interconnection block for combining these intervals into an output signal having predetermined relationships among the intervals, an output block for transmitting the output signal to a load, and, optionally, a filter for removing unwanted frequency components from the output signal and an adjustment block for selecting from among a plurality of output signals with predetermined characteristics. The output is a repeating succession of a burst of rectangular waves, an equalizing pulse (if needed) to cancel net DC, and a rest period of no signal.

Abstract: A cast punch and mounting assembly for forming an opening in an orthopedic cast and securing a therapeutic treatment device within the opening adjacent a bone or musculoskeletal injury is provided. The assembly includes a cast punch housing which is fastened to the body surface beneath the cast. The cast punch housing includes a central bore and a guide rod extending outwardly from the central bore. The guide rod extends through the cast. A punch member and a drive member are operably connected to the guide rod and are movable towards the central bore of the cast punch housing to core an opening in the cast above the central bore. The central bore includes engagement structure to releasably secure a therapeutic treatment device within the central bore of the cast punch housing.

Abstract: Apparatus and method for providing PEMF therapy to selected portions of a patient's body such as the hips and spine. The apparatus preferably includes at least two transducer coils. Electronics for driving the coils are contained in a housing. The housing is preferably connected to the transducer coil by a flexible cable. The housing preferably includes a battery power supply.

Abstract: A multi-functional portable electro-medical device provides interferential current stimulation to promote bone growth. Two electrical signals are applied to a target area, each electrical signal being formed by a set of two electrode pads. A beat frequency is created at the location the signals intersect with each other. The beat frequency is the difference between the frequencies of the two signals and has an amplitude that is additive and greater than either signal alone. The depth of the interferential signal is increased by increasing the carrier frequency of the signals. The direction of the interferential signal shifts toward the signal having the lower amplitude. The electrical stimulation is used in combination with biologics to further increase bone growth. The target area is large enough to include multiple vertebral segments.

Abstract: The apparatus is used for therapeutically treating injuries using ultrasound. The present invention may include a therapeutic ultrasonic composite comprising a transducer and an integrated circuit unit positioned adjacent the transducer. The therapeutic ultrasonic composite also includes signal generation circuitry, housed on the integrated circuit unit, for generating a driving signal for the transducer, and a driving interface between the signal generation circuitry and the transducer. In operation, driving signals generated by the signal generation circuitry are transmitted to the transducer by the interface, thereby driving the transducer for the creation of therapeutic ultrasound.

Abstract: Non-invasive therapeutic treatment of bone in vivo using ultrasound in conjunction with application of a biochemical compound or bone growth factor is performed by subjecting bone to an ultrasound signal supplied to an ultrasound transducer placed on the skin of a bony member, and involving a repetitive finite duration signal consisting of plural frequencies that are in the ultrasonic range to 20 MHz. Concurrent with application of the ultrasound is the utilization of a bone growth factor applied to the skin of a bony member before stimulation with ultrasound. Ultrasonic stimulation is operative to transport the bone growth factor to the bone and then to synergistically enhance the interaction of the bone growth factor with the bone, whereby to induce healing, growth and ingrowth responses. In another embodiment, a vibrational or mechanical input together with a biochemical compound enhances both bone fracture healing and treats osteoporosis.

Abstract: A spinal fusion stimulator comprising an interbody fusion cage or other interbody fixation device adapted to be implanted in the intervertebral disc space of a patient's spine, the interbody fusion cage in the preferred embodiment having a hollow body with internal and external conductive surfaces. The stimulator includes a constant current generator connected to the interbody fusion cage and set to provide a DC current effective to produce a surface current density of at least 1 &mgr;A/cm2 in the interbody fusion cage when implanted.

Abstract: Non-invasive therapeutic treatment of bone in vivo using ultrasound in conjunction with application of a biochemical compound or bone growth factor is performed by subjecting bone to an ultrasound signal supplied to an ultrasound transducer placed on the skin of a bony member, and involving a repetitive finite duration signal consisting of plural frequencies that are in the ultrasonic range to 20 MHz. Concurrent with application of the ultrasound is the utilization of a bone growth factor applied to the skin of a bony member before stimulation with ultrasound. Ultrasonic stimulation is operative to transport the bone growth factor to the bone and then to synergistically enhance the interaction of the bone growth factor with the bone, whereby to induce healing, growth and ingrowth responses. In another embodiment, a vibrational or mechanical input together with a biochemical compound enhances both bone fracture healing and treats osteoporosis.

Abstract: An electrical bone growth promotion apparatus and method for the delivery of electrical current to an implant surgically implanted within the intervertebral space between two adjacent vertebrae of the spine to promote bone growth and the fusion process to areas adjacent to the implant. The apparatus of the present invention comprises a self contained implant having a surgically implantable, renewable power supply and related control circuitry for delivering electrical current directly to the implant and thus directly to the area in which the promotion of bone growth is desired. The desired areas of bone growth promotion may be controlled by conducting negative charge only to the desired location of bone growth promotion.

Abstract: An implantable bone growth stimulator comprising an electrical signal generator having an anode connected thereto along with a prefabricated flexible wire mesh cathode that is extendable to at least twice its preformed initial length. The cathode in a preferred embodiment includes a single chain of conductive wire links formed as alternating loops and twists of two strands of monofilament titanium wire.

Abstract: Methods for healing bone fractures are provided. The methods as provided herein involve the application of resonant frequency stimulation to promote fracture healing and also to diagnose status of fracture healing. The methods of the present invention are particularly desirable because they are site-specific, non-invasive and require a minimum amount of early healing or callus formation.

Abstract: Implantable device, such as a femoral head prosthesis, with a body (12) of biocompatible material shaped to suit its medical function, which forms an internal cavity (16) and has open apertures (18) that lead from the cavity (16) to the outside. The cavity (16) serves to receive spongiosa or other biological material into which the tissue that surrounds the implanted device is intended to grow through the apertures (18). The device is provided with at least two electrodes (30, 32), at least one of which is located in the cavity (16) spaced apart from the inside of the body (12) that forms the cavity (16). The electrodes are provided with an arrangement for supplying a low-frequency alternating voltage, so that by means of the supplied voltage a low-frequency electrical alternating field and a low-frequency alternating current, whereby the tissue growth is promoted, are created inside the cavity (16).

Abstract: An apparatus provides relief from osteoporosis, through either prevention of its development or reversal of its presence, by utilizing a light-weight portable low intensity, low frequency electrical field specifically targeted for osteoporotic of hips and spine, thereby reducing the growing numbers of hip and vertebral fractures in our aging population. The apparatus is simple to utilize, safe, of inexpensive construction, convenient to use, and may be incorporated permanently within a specific designer line of clothing made for this purpose, or the device may be portable and adaptable to a variety of clothing which the wearer may choose, as that person's fashion preferences may dictate. The hip areas of the official pants are padded to absorb energy if the wearer accidentally falls onto either hip, decreasing the likelihood of a hip fracture.

Abstract: A method is provided for the repair of a bone defect in a patient which employs a bone growth-stimulating composition derived from healthy cancellous bone.

Abstract: Disclosed herein is a method for preventing osteoporosis in a human patient by contacting the patient with an electromagnetic (EM) capture and generator device for a time effective for preventing the disease.

Abstract: A hand-held programmer/monitor (500) for programming and monitoring an implantable tissue growth stimulator (10) is provided. The stimulator (10) includes circuitry (46) for implementing selected operations in response to a down-link signal transmitted by the programmer/monitor (500). The stimulator (10) also includes circuitry (14) for transmitting up-link signals to the programmer/monitor (500). The programmer/monitor (500) includes a control circuit (518) for generating the down-link signal. The control circuit (518) also processes the up-link signal to monitor the status of the implantable tissue growth stimulator (10). The programmer/monitor (500) also includes a transmit/receive circuit (514) for transmitting the down-link signal to and for receiving the up-link signal from the implantable tissue growth stimulator (10). The transmit/receive circuit (514) also couples the up-link signal to the control circuit (518).

Abstract: A method and apparatus for accelerating osseointegration of titanium implants in bone to anchor a prosthetic or dental device thereon in which an alternating electric signal of symmetrical wave form and of substantially constant amplitude having a frequency in the range of from about 40 to 100 KHz and providing a constant current in the range of from about 10 to 100 microamperes is supplied to at least one electrode in contact with the metal implant and another electrode in contact with the skin in proximity to the implant.

Abstract: The present invention relates to a method and device for the iontophoretic delivery of a therapeutic dose range of bisphosphonate to be delivered to a patient over a period of lime to prevent the onset for advancement of osteoporosis and other metabolic bone diseases for a selected period of time.

Abstract: A method for preventing the onset or advancement of osteoporosis or other metabolic bone disorders in a patient by iontophoretically administering to the patient an effective amount of a bisphosphonate which would be effective for preventing the onset or advancement of osteoporosis or other bone disorders and wherein the effective amount of bisphosphonate is delivered over a period of from about four (4) hours to about forty-eight (48) hours, at intervals of from about once a week to about twice a year and wherein the effective amount of bisphosphonate also contains an agent capable of chelating calcium.

Abstract: A hand-held programmer/monitor (500) for programming and monitoring an implantable tissue growth stimulator (10) is provided. The stimulator (10) includes circuitry (46) for implementing selected operations in response to a down-link signal transmitted by the programmer/monitor (500). The stimulator (10) also includes circuitry (46) for transmitting up-link signals to the programmer/monitor (500). The programmer/monitor (500) includes a control circuit (518) for generating the down-link signal. The control circuit (518) also processes the up-link signal to monitor the status of the implantable tissue growth stimulator (10). The programmer/monitor (500) also includes a transmit/receive circuit (514) for transmitting the down-link signal to and for receiving the up-link signal from the implantable tissue growth stimulator (10). The transmit/receive circuit (514) also couples the up-link signal to the control circuit (518).

Abstract: The apparatus is used for therapeutically treating injuries using ultrasound. The apparatus includes an ergonomically constructed ultrasonic transducer treatment head module partially fabricated with a conductive plastic material. The apparatus also utilizes a portable, ergonomically constructed main operating unit constructed to fit within a pouch worn by the patient. In operation, the transducer treatment head module is positioned adjacent the area of the injury and excited for a predetermined period of time. To ensure that the transducer treatment head module is properly positioned, and to insure compliance with a treatment protocol, a safety interlock is provided to prevent inadvertent excitation of the transducer.

Abstract: A device (10, 18) stimulates with an ultrasound the growth of a tissue or produces an image at a site within a patient. A housing (12, 20, 22) may be subcutaneously implanted within the patient such that the ultrasound is directed toward the site. A generator (52), disposed within the housing (12, 20, 22), produces a signal, which a transducer (56, 84, 144) converts into the ultrasound. The transducer (56, 84, 144) is partially disposed within the housing (12, 20, 22). The device (10, 18) may include an imaging circuit (80) for processing ultrasound echoes received by the transducer (56, 84, 144) to generate images of the tissue at the site. A remote control (102) may be used to control the device (10, 18) while it is implanted within the patient.

Abstract: A transducer for non-invasive transcutaneous transmission of pulsed ultrahigh-frequency acoustic radiation, in body tissue and/or fluids adjacent a bone fracture is "on target" when a fraction of the propagated energy within the longitudinal-response lobe of the transducer encounters a crack or other open feature of the fracture, where a gap or space exists between closely spaced fracture walls. The ultrahigh-frequency acoustic radiation sees this "on target" feature as the entrance to a waveguide, whereby pulsed ultrahigh-frequency acoustic radiation is guided within the crack. When this acoustic radiation encounters a gap of at least a quarter wavelength (at the ultrahigh frequency), a standing wave condition establishes itself, with dissipation of the ultrahigh frequency and with demodulation to establish a therapeutically beneficial low-frequency acoustic condition, within the fracture, and acting where most needed, namely, on and between wall regions of adjacent fragments of the broken bone.

Abstract: An apparatus and method for regulating the growth of living tissue are provided. The apparatus includes a deformable magnetic field generator and a magnetic field detector for producing a controlled, fluctuating, directionally oriented magnetic field parallel to a predetermined axis projecting through the target tissue. The deformable magnetic field generator includes a pair of field coils embedded in a flexible material which allows the field coils to be plastically deformed to fit the contour of a body region such as a patient's limb. The field detector samples the magnetic flux density along the predetermined access and provides a signal to a microprocessor which determines the average value of the flux density. The applied magnetic field is oscillated at predetermined frequencies to maintain a preselected ratio of frequency to average flux density.

Abstract: Non-invasive apparatus for accelerating the process of jawbone healing and regeneration, reattachment of traumatically loosened teeth to the jawbone, or osseointegration of implants in a patient, including at least one piezoelectric transducer and connections to transmit ultrasonic frequency electrical current to the piezoelectric transducer. The ultrasonic frequency electrical current transmitted to the piezoelectric transducer causes the transducer to contract and expand volumetrically in response to a changing electrical field to generate pressure wave vibrations of ultrasonic frequency that are coupled to the bone.

Abstract: An apparatus and method for regulating tissue growth in vivo are provided. The apparatus includes a magnetic field generator and a magnetic field detector for producing a controlled, fluctuating, directionally oriented magnetic field parallel to a predetermined axis projecting through the target tissue. The field detector samples the magnetic flux density along the predetermined access and provides a signal to a microprocessor which determines the average value of the flux density. The applied magnetic field is oscillated at predetermined frequencies to maintain a preselected ratio of frequency to average flux density. This ratio is maintained by adjusting the frequency of the fluctuating magnetic field and/or by adjusting the intensity of the applied magnetic field as the composite magnetic flux density changes in response to changes in the local magnetic field to which the target tissue is subjected.

Abstract: Invented are methods and an apparatus for faradic stimulation of osteogenesis by control of electrochemical reactions through maintenance of a stimulus between a cathode and anode yielding only beneficial electrochemical reactions at the cathode, the site of desired osteogenesis, while preventing any detrimental reaction at the same. Said methods and apparatus maintain a stimulus yielding the maximum acceptable level of oxygen consumption and pH elevation at the cathode, either with or without the formation of hydrogen peroxide as only an intermediate chemical species, while preventing the initiation of hydrogen gas evolution at the same such that the stimulus results in depression of oxygen tension plus elevation of pH, environmental effects that favor osteogenesis, and prevents a reaction resulting in elevation of pH plus hydrogen gas evolution, the latter effect being detrimental to the same.

Abstract: A method for the therapeutic stimulation of bone growth of a bone site is disclosed comprising the steps of implanting first and second electrodes into the tissue near the base site. The electrodes are coupled to a bone growth stimulator which generates an alternating current.

Abstract: Applicator coil for an electromagnetic therapy apparatus, which has substantially the form of a zone of a sphere deformed into an oval and which is suited above all to rendering a low frequency magnetic alternating field operative on projecting parts of the human or animal body, such as the shoulder region or the face of the person.

Abstract: A device for stimulating bone tissue by applying a low level alternating current signal directly to the patient's skin. A crystal oscillator, a binary divider chain and digital logic gates are used to generate the desired waveforms that reproduce the natural electrical characteristics found in bone tissue needed for stimulating bone growth and treating osteoporosis. The device, powered by a battery, contains a switch allowing selection of the correct waveform for bone growth stimulation or osteoporosis treatment so that, when attached to the skin of the patient using standard skin contact electrodes, the correct signal is communicated to the underlying bone structures.

Abstract: The invention relates to a method for stimulating bone growth in a mammal. The method comprises the step of exposing a bone zone where bone growth is to occur to cavitation for bringing forth haemorrhage and/or microfissures and/or to at least partially loosened bone chips at said bone zone.

Abstract: A medical treatment installation having an imaging system and a transmitter which generates a focused therapy field, such as focused shockwaves, for treating a pathology in a region of a patient includes components for displacing the position of the focal point of the therapy field relative to the region to be treated so that the focus therapy field is successively incident at a number of locations in the region during treatment, and a mark generator, which interacts with the imaging system, for generating an indicator in the image corresponding to each of the locations of the focused therapy field in the region. The mark may identify each location at which the region has been subjected to the therapy field during treatment, so that repetitive administration of the therapy field at a location which has already been treated can be avoided.

Abstract: A method including applying varying signals to a first electrode at the tissue site and a second electrode remote from the tissue site and monitoring the results to determine a distinctive transition in the current-voltage characteristics of the electrode pair. A signal is then selected and applied to the electrodes to operate beyond the transition. Periodically, a varying signal is applied to the electrodes and the monitoring process reperformed to determine a new transition and an appropriate signal is selected to operate beyond the transition.