Blocking pain using alternating electric fields

Abstract

Pain can be blocked in a living subject by positioning a plurality of electrodes at respective locations on the subject's body and applying an AC signal between the plurality of electrodes. The amplitude and frequency characteristics of the AC signal are such that when the AC signal is applied to the electrodes, the AC signal will block pain at the target site. The AC signal has a given frequency between 50 kHz and 1 MHz and an amplitude between 75% and 150% of a threshold. The threshold is either (a) determined based on a test performed on the subject to determine the subject's lowest amplitude at which electrical sensations are experienced at the given frequency or (b) determined based on previously obtained data specifying the lowest amplitude at which electrical sensations are experienced by a majority of subjects at the given frequency.

Description

[0001] Cross-reference to related applications

[0002] This application claims the benefit of U.S. Provisional Application 63 / 568,197, filed March 21, 2024, the full text of which is incorporated herein by reference. Background Technology

[0003] Hundreds of millions of people experience pain every day, and managing pain can often be a daunting task. Conventional methods for pain management include broad-spectrum medications (many of which can be dangerous and / or addictive) and various non-pharmacological approaches. However, in many cases, conventional methods fail to achieve the desired goal of safely eliminating or improving a subject's pain. Therefore, there is a strong need for additional methods for pain management. Summary of the Invention

[0004] One aspect of the invention relates to a first method for blocking pain experienced by a subject at a target site on the subject's body. The first method includes positioning a plurality of electrodes at corresponding locations on the subject's body and applying a first AC signal between the plurality of electrodes. These corresponding locations are selected such that when the first AC signal is applied between the plurality of electrodes, the first AC signal will block pain at the target site. The amplitude and frequency characteristics of the first AC signal are such that when the first AC signal is applied between the plurality of electrodes, the first AC signal will block pain at the target site. The first AC signal has a given frequency between 50 kHz and 1 MHz and an amplitude between 75% and 150% of a threshold. This threshold is determined (a) based on a test performed on the subject to determine the minimum amplitude at which the subject experiences an electrical sensation at that given frequency; or (b) based on previously obtained data specifying the minimum amplitude at which most subjects experience an electrical sensation at that given frequency.

[0005] In some instances of this first method, the threshold is determined based on the test performed on the subject. In some instances of this first method, the threshold is based on previously obtained data that specifies the minimum amplitude at which at least 80% of the subjects experience an electrical sensation at a given frequency.

[0006] In some instances of the first method, the threshold is determined prior to the application by: applying a second AC signal to the subject's body at the given frequency; increasing the amplitude of the second AC signal until the subject begins to experience an electrical sensation; recording the amplitude of the second AC signal when the subject begins to experience an electrical sensation; and using the recorded amplitude as the threshold.

[0007] Optionally, in the example described in the previous paragraph, the second AC signal is applied to the subject's body after positioning using the multiple electrodes. Optionally, in the example described in the previous paragraph, the first AC signal has an amplitude between 80% and 99% of the threshold. Optionally, in the example described in the previous paragraph, the first AC signal has an amplitude between 100% and 120% of the threshold.

[0008] In some instances of this first method, the given frequency is determined prior to the application by: applying a second AC signal to the subject's body, wherein the second AC signal is maintained at a specific amplitude; decreasing the frequency of the second AC signal until the subject begins to experience an electrical sensation; recording the frequency of the second AC signal when the subject begins to experience an electrical sensation; and using the recorded frequency as the given frequency. In these embodiments, the threshold corresponds to the specific amplitude of the second AC signal.

[0009] Alternatively, in the example described in the previous paragraph, the second AC signal is applied to the subject's body after positioning using the multiple electrodes.

[0010] In some instances of the first method, the given frequency and the threshold are determined prior to the application by: applying a second AC signal to the subject's body; changing the frequency of the second AC signal according to a periodic frequency variation curve, and increasing the amplitude of the second AC signal while changing the frequency; recording the frequency and amplitude of the second AC signal when the subject begins to experience an electric sensation; and using the recorded frequency as the given frequency and the recorded amplitude as the threshold.

[0011] Optionally, in the example described in the previous paragraph, the periodic frequency variation curve causes the frequency characteristics of the second AC signal to decrease from a maximum frequency to a minimum frequency during the first part of a single periodic operating cycle, maintain the frequency of the second AC signal at the minimum frequency during the second part of the periodic cycle, and increase the frequency of the second AC signal to the maximum frequency during the third part of the periodic cycle.

[0012] In some instances of the first method, the locations where the plurality of electrodes are positioned are selected such that the target region is situated between the plurality of electrodes. In some instances of the first method, the plurality of electrodes are positioned proximally relative to the target region. In some instances of the first method, at least one of the electrodes is positioned proximally relative to the target region, and at least one of the electrodes is positioned distally relative to the target region.

[0013] In some instances of the first method, the first AC signal has a frequency between 90 kHz and 300 kHz. In some instances of the first method, the first AC signal comprises a periodic sequence of AC voltage pulses, each pulse having a duration of less than 50 ms, and the periodic sequence having a period between 100 ms and 2 seconds. In some instances of the first method, the first AC signal comprises a sequence of AC voltage pulses, each pulse having a duration of less than 50 ms, and the consecutive pulses within the sequence are spaced 100 ms to 2 seconds apart.

[0014] Another aspect of the invention relates to a first device for blocking pain experienced by a subject at a target site on the subject's body. The first device includes an AC voltage source and a controller. The AC voltage source is configured to generate a first AC signal. The controller is configured to control the operation of the AC voltage source such that (a) the amplitude and frequency characteristics of the first AC signal are such that when the first AC signal is applied between a plurality of electrodes positioned at corresponding locations on the subject's body, the first AC signal will block pain at the target site; (b) the first AC signal has a given frequency between 50 kHz and 1 MHz; and (c) the first AC signal has an amplitude between 75% and 150% of a threshold. This threshold is determined (a) based on a test performed on the subject to determine the minimum amplitude at which the subject experiences an electrical sensation at that given frequency; or (b) based on previously obtained data specifying the minimum amplitude at which most subjects experience an electrical sensation at that given frequency.

[0015] In some embodiments of the first device, the threshold is determined based on the test performed on the subject, and the controller is further configured to: (a) control the operation of the AC voltage source during the test performed on the subject, such that the AC voltage source (i) applies a second AC signal to the subject's body at the given frequency, and (ii) increase the amplitude of the second AC signal until the subject begins to experience an electric sensation; (b) record the amplitude of the second AC signal when the subject begins to experience an electric sensation; and (c) use the recorded amplitude as the threshold.

[0016] Optionally, in the example described in the preceding paragraph, the amplitude of the first AC signal is set between 80% and 99% of the threshold. Optionally, in the example described in the preceding paragraph, the amplitude of the first AC signal is set between 100% and 120% of the threshold.

[0017] In some embodiments of the first device, the first AC signal has a frequency between 90 kHz and 300 kHz. In some embodiments of the first device, the first AC signal comprises a periodic sequence of pulse trains of AC voltage, wherein each pulse train has a duration of less than 50 ms, and wherein the periodic sequence has a period between 100 ms and 2 seconds. In some embodiments of the first device, the first AC signal comprises a sequence of pulse trains of AC voltage, wherein each pulse train has a duration of less than 50 ms, and wherein consecutive pulse trains within the sequence are spaced 100 ms to 2 seconds apart.

[0018] In some embodiments of the first device, the threshold is determined based on the test performed on the subject, and the controller is further configured to: (a) control the operation of the AC voltage source during the test performed on the subject, such that the AC voltage source (i) applies a second AC signal to the subject's body, wherein the second AC signal is maintained at a specific amplitude, and (ii) decrease the frequency of the second AC signal until the subject begins to experience an electric sensation; (c) record the frequency of the second AC signal when the subject begins to experience an electric sensation; and (d) use the recorded frequency as the given frequency. In these embodiments, the threshold corresponds to the specific amplitude of the second AC signal.

[0019] In some embodiments of the first device, the threshold is determined based on the test performed on the subject, and the controller is further configured to: (a) control the operation of the AC voltage source during the test performed on the subject, such that the AC voltage source (i) applies a second AC signal to the subject's body, (ii) changes the frequency of the second AC signal according to a periodic frequency variation curve, and (iii) increases the amplitude of the second AC signal while changing the frequency; record the frequency and amplitude of the second AC signal when the subject begins to experience an electric sensation; and use the recorded frequency as the given frequency and the recorded amplitude as the threshold.

[0020] Optionally, in the embodiment described in the previous paragraph, the periodic frequency variation curve causes the frequency characteristics of the second AC signal to decrease from a maximum frequency to a minimum frequency during the first part of a single periodic operating cycle, maintain the frequency of the second AC signal at the minimum frequency during the second part of the periodic cycle, and increase the frequency of the second AC signal to the maximum frequency during the third part of the periodic cycle.

[0021] In some embodiments of the first device, the threshold is based on previously obtained data that specifies the minimum amplitude at which at least 80% of subjects experience an electrical sensation at a given frequency.

[0022] Another aspect of the invention relates to a second method for blocking pain experienced by a subject at a target site on the subject's body. The second method includes positioning a plurality of electrodes at corresponding locations on the subject's body and applying a first AC signal between the plurality of electrodes. These corresponding locations are selected such that when the first AC signal is applied between the plurality of electrodes, the first AC signal will block pain at the target site. The amplitude and frequency characteristics of the first AC signal are such that when the first AC signal is applied between the plurality of electrodes, the first AC signal will block pain at the target site. The first AC signal has a given frequency between 50 kHz and 1 MHz.

[0023] In some instances of the second method, the first AC signal has an amplitude of at least 30V peak-to-peak value. In some instances of the second method, the first AC signal has an amplitude of 30V to 90V peak-to-peak value.

[0024] In some instances of this second method, the amplitude of the first AC signal is set to at least 25% of a threshold, and the threshold is determined based on a test performed on the subject to find the lowest amplitude at which the subject experiences an electrical sensation at a given frequency.

[0025] In some instances of this second method, the amplitude of the first AC signal is set to 50% to 100% of a threshold, and the threshold is determined based on a test performed on the subject to find the lowest amplitude at which the subject experiences an electrical sensation at a given frequency.

[0026] Optionally, in the examples described in the preceding paragraph, the threshold is determined before application by: applying a second AC signal to the subject's body at the given frequency; increasing the amplitude of the second AC signal until the subject begins to experience an electrical sensation; recording the amplitude of the second AC signal when the subject begins to experience an electrical sensation; and using the recorded amplitude as the threshold. Optionally, in these examples, the second AC signal is applied to the subject's body after localization using the multiple electrodes.

[0027] In some instances of the second method, the amplitude of the first AC signal is set to 50% to 100% of a threshold determined based on a test performed on the subject to find the lowest amplitude at which the subject experiences an electrical sensation at a given frequency, and the first AC signal has an amplitude between 80% and 99% of that threshold.

[0028] In some instances of this second method, the given frequency is determined prior to the application by: applying a second AC signal to the subject's body, wherein the second AC signal is maintained at a specific amplitude; decreasing the frequency of the second AC signal until the subject begins to experience an electrical sensation; recording the frequency of the second AC signal when the subject begins to experience an electrical sensation; and using the recorded frequency as the given frequency. Optionally, in these instances, the second AC signal is applied to the subject's body after positioning using the multiple electrodes.

[0029] In some instances of the second method, the locations where the plurality of electrodes are positioned are chosen such that the target region is situated between the plurality of electrodes. In some instances of the second method, the plurality of electrodes are positioned proximally relative to the target region. In some instances of the second method, at least one of the electrodes is positioned proximally relative to the target region, and at least one of the electrodes is positioned distally relative to the target region.

[0030] In some instances of the second method, the first AC signal has a frequency between 90 kHz and 300 kHz. In some instances of the second method, the first AC signal comprises a sequence of pulse trains of AC voltage, each pulse train having a duration of less than 50 ms, and the interval between consecutive pulse trains within the sequence being 100 ms to 2 seconds.

[0031] Another aspect of the invention relates to a second device for blocking pain experienced by a subject at a target site on the subject's body. The second device includes an AC voltage source and a controller. The AC voltage source is configured to generate a first AC signal. The controller is configured to control the operation of the AC voltage source such that (a) the amplitude and frequency characteristics of the first AC signal are such that when the first AC signal is applied between a plurality of electrodes positioned at corresponding locations on the subject's body, the first AC signal will block pain at the target site; (b) the first AC signal has a given frequency between 50 kHz and 1 MHz; and (c) the first AC signal has an amplitude between 50% and 100% of a threshold. This threshold is determined based on a test performed on the subject to find the lowest amplitude at which the subject experiences an electrical sensation at that given frequency.

[0032] In some embodiments of the second device, the controller is further configured to perform the test by: (a) controlling the operation of the AC voltage source such that the AC voltage source (i) applies a second AC signal to the subject's body at the given frequency, and (ii) increases the amplitude of the second AC signal until the subject begins to experience an electric sensation; (b) recording the amplitude of the second AC signal when the subject begins to experience an electric sensation; and (c) using the recorded amplitude as the threshold. Optionally, in these embodiments, the amplitude of the first AC signal is set between 80% and 99% of the threshold.

[0033] In some embodiments of the second device, the first AC signal has a frequency between 90 kHz and 300 kHz. In some embodiments of the second device, the first AC signal comprises a sequence of pulse trains of AC voltage, each pulse train having a duration of less than 50 ms, and the consecutive pulse trains within the sequence are spaced 100 ms to 2 seconds apart.

[0034] In some embodiments of the second device, the controller is further configured to perform the test by: (a) controlling the operation of the AC voltage source while performing the test on the subject, such that the AC voltage source (i) applies a second AC signal to the subject's body, wherein the second AC signal is maintained at a specific amplitude, and (ii) decreasing the frequency of the second AC signal until the subject begins to experience an electric sensation; (b) recording the frequency of the second AC signal when the subject begins to experience an electric sensation; and (c) using the recorded frequency as the given frequency. In these embodiments, the threshold corresponds to the specific amplitude of the second AC signal. Attached Figure Description

[0035] Figure 1A A device for blocking pain is described, comprising electrodes positioned on the subject's arm and an AC power source that applies AC signals to these electrodes.

[0036] Figure 1B Describing the use of Figure 1A The electrodes are attached to a strap on the subject's arm.

[0037] Figure 2 The periodic frequency variation in an example of an AC signal that can provide pain-blocking effects is depicted.

[0038] Figure 3 This is a graph illustrating the voltage level of an AC signal at a given frequency applied to a subject as a sequence of several pulse trains.

[0039] Figure 4 This is a flowchart illustrating an example of a pain-blocking procedure.

[0040] Various embodiments will now be described in detail with reference to the accompanying drawings, wherein the same reference numerals denote the same elements. Detailed Implementation

[0041] This application relates to systems, apparatus, methods, and other embodiments for applying an electric field to a region of a subject's body to achieve a pain-blocking effect on pain experienced by the subject, the pain originating from a region of the subject's body (referred to as a "target site" or "pain area"). It should be noted that the region where the electric field is applied and the pain area / target site do not necessarily overlap.

[0042] Tumor Therapeutic Fields (TTFields) therapy is a proven cancer treatment method that uses an alternating electric field with frequencies, for example, between 50 kHz and 1 MHz (more commonly 100 kHz to 300 kHz). The alternating electric field is induced by electrode assemblies (e.g., an array of capacitively coupled electrodes, also known as a transducer array) placed on opposite sides of the subject's skin in a region of the body. An alternating electric field is formed in this region when an AC voltage is applied between the opposing electrode assemblies.

[0043] When subjects are treated with alternating electric fields, the efficacy of the treatment is strongly dependent on the duration of application of the alternating electric field. For example, when TTFields are used to treat tumors, it is preferable to apply the alternating electric field for at least 14 hours per day, and preferably even longer. Furthermore, higher amplitude is closely associated with higher therapeutic efficacy. However, as the amplitude of the alternating electric field increases and / or as the frequency of the alternating electric field decreases (e.g., to around 100 kHz), some subjects experience an unpleasant sensation referred to herein as “electrosensory sensation.” This electrosensory sensation may be, for example, a vibrational sensation in muscle fibers, paresthesia, and / or a twitching or contraction sensation. The inventors believe that the electrosensory sensation originates from the interaction between the alternating electric field and nerve cells (i.e., neurons) located near or adjacent to the electrode assembly.

[0044] Electrosensory sensation is a problem when using alternating electric fields (e.g., TTFields) to treat subjects, as it may cause some subjects to reduce the amount of time the alternating electric field is applied each day (which reduces the efficacy of the treatment). In extreme cases, electrosensory sensation may even cause some subjects to discontinue treatment. However, the inventors have discovered beneficial side effects associated with electrosensory sensation. More specifically, pain experienced by a subject in certain areas of their body can be blocked or at least partially relieved at or around the combination of amplitude and frequency at which electrosensory sensation occurs. And in many cases, the pain-blocking effect will occur at significantly lower amplitudes. In some embodiments, this pain-blocking effect is achieved by intentionally inducing electrosensory sensation. In other embodiments, the pain-blocking effect can be achieved without inducing electrosensory sensation by setting the amplitude to a lower level (e.g., 80%, 50%, or even 25% of the amplitude that would trigger electrosensory sensation in the subject's body).

[0045] Some embodiments block pain experienced by a subject at a target site on the subject's body. These embodiments include an AC voltage source and a controller configured to generate a first AC signal, the controller being configured to control the operation of the AC voltage source such that (a) the amplitude and frequency characteristics of the first AC signal are such that when the first AC signal is applied between multiple electrodes positioned at corresponding locations on the subject's body, the first AC signal will block pain at the target site; (b) the first AC signal has a given frequency between 50 kHz and 1 MHz; and (c) the first AC signal has an amplitude between 75% and 150% of a threshold. This threshold is determined either (a) based on a test performed on the subject to determine the minimum amplitude at which the subject experiences an electrical sensation at that given frequency; or (b) based on previously obtained data specifying the minimum amplitude at which most subjects experience an electrical sensation at that given frequency.

[0046] Some embodiments block pain experienced by a subject at a target site on the subject's body. These embodiments include an AC voltage source and a controller configured to generate a first AC signal, the controller being configured to control the operation of the AC voltage source such that (a) the amplitude and frequency characteristics of the first AC signal are such that when the first AC signal is applied between multiple electrodes positioned at a corresponding location on the subject's body, the first AC signal will block pain at the target site; (b) the first AC signal has a given frequency between 50 kHz and 1 MHz; and (c) the first AC signal has an amplitude between 50% and 100% of a threshold. The threshold in these embodiments is determined based on a test performed on the subject to find the lowest amplitude at which the subject experiences an electrosensory sensation at that given frequency.

[0047] Figure 1A A device 100 for blocking pain experienced by a subject is depicted. Device 100 includes a plurality of electrodes 110 positioned at corresponding locations on a subject's forearm 102. Note that the electrodes 110 can be positioned at other locations on the body, typically near the area where the subject is experiencing pain. The electrodes 110 can be deployed to surround the area where the subject is experiencing pain, such that a target site 104 (the location where the subject is experiencing pain) is located between the electrodes 110. For example, at least one electrode of the electrodes 110 can be positioned proximally relative to the target site 104, and at least one electrode of the electrodes 110 can be positioned distally relative to the target site, such as... Figure 1A As depicted. However, it should be noted that the deployment of electrodes may result in the area where the current is applied not necessarily overlapping with the area of ​​pain. For example, in Figure 1A In this study, electrodes are positioned on the subject's forearm, but applying alternating current through these electrodes to create an electric field (the electrical properties of which are determined in a manner described in more detail below) can, in some cases, block or alleviate pain in another part of the arm located distal to the electrodes (e.g., the wrist).

[0048] Various electrodes may be used in the embodiments described herein, including but not limited to those described in US 2023 / 0043071 entitled “Electrode Assembly for Applying Tumor Treating Fields (TTFields) that Include a Sheet of Graphite”, US 2021 / 0402179 entitled “Flexible Transducer Arrays with a Polymer Insulating Layer for Applying Tumor Treating Fields (TTFields)”, US 2021 / 0402179 entitled “Flexible Transducer Arrays with a Polymer Insulating Layer for Applying Tumor Treating Fields (TTFields)”, and those described in US 2021 / 0402179 entitled “Composite”. The electrode assembly described in U.S. Patent 8,715,203, entitled "electrode (composite electrode)," is incorporated herein by reference in its entirety.

[0049] Electrodes 110, positioned on body parts of the subject (e.g., the subject's arm, leg, back, etc.), can be secured to the skin using conductive adhesives (such as conductive hydrogel adhesives or conductive non-hydrogel polymer adhesives). To further secure the electrodes to the skin and maintain their positioning on the subject's body parts, additional electrode fixation mechanisms can be used. For example, Figure 1B A retaining band 160 wrapped around the electrode 110 is shown (typically shown in dashed lines through the electrode 110, which is not normally visible through the band 160). The band 160 can be made of a stretchable / flexible material that can be used with body parts of different sizes and contours, and can also be configured to operate to press the electrode (or electrode assembly) against the subject's body. Such stretchable / flexible materials can include breathable materials (e.g., cotton fabric) through which sweat can pass. The stretchable / flexible band 160 can be a reusable band, in which case it can include fasteners (not shown) (such as hook and loop fasteners (e.g., Velcro®)) attached to opposite ends of the band to allow for adjustable tightening of the band, thereby forming a closed loop around body parts of different sizes. Other types of fastening mechanisms can be used, including various adhesive materials, buckle fasteners, etc. Alternatively, Figure 1B The bandage 160 may be a disposable bandage, such as a bandage (e.g., an adhesive bandage), the front surface (the surface that contacts the subject's skin) of which is at least partially covered with an adhesive layer in order to secure the bandage to the body part.

[0050] Return to Figure 1A The device 100 also includes an AC voltage source 130 configured to generate an AC signal and apply it to the electrodes 110, which in turn applies an alternating electric field in the region 104 between the electrodes 110. It should be noted that, although... Figure 1A and Figure 1B Two electrodes 110 are depicted above region 104 and two electrodes 110 are depicted below region 104, but the number of electrodes on each side of region 104 may vary (e.g., between 1 and 20). When the electrical characteristics of the generated AC signal are suitable for specific values ​​(e.g., a predetermined threshold voltage and a specific frequency), the applied electric field will achieve a pain-blocking effect on pain emanating from the subject's region ("pain area" or "pain site"). (As noted above, the pain area is not necessarily located within region 104 where the electric field is formed). AC voltage source 130 is configured to apply an AC voltage with a frequency between 50 kHz and 1 MHz, and its voltage level will typically be in the range of 50 VRMS to 150 VRMS or 20 VRMS to 150 VRMS.

[0051] exist Figure 1AIn the depicted embodiments, the AC voltage source 130 and the device 100 are typically controlled by a controller 140 (e.g., a processor-based controller). The controller 140 controls the characteristics of the voltage delivered by the AC voltage source 130 (including amplitude and frequency, and optionally other characteristics such as waveform and duty cycle). This control can be based on previously determined electrical characteristics of a specific subject, and when applied to a specific subject (and possibly to a specific location using a specific electrode arrangement), such that pain experienced by the subject is blocked. As will be discussed in more detail below, the controller 140 can also be configured to control the AC source voltage 130 while performing tests to determine the electrical characteristics of the AC signal (e.g., the minimum amplitude at which the subject experiences an electrosensory sensation at a given frequency), which will help block or alleviate pain experienced by the subject.

[0052] In some embodiments, the controller 140 further controls the operation of the AC voltage source (including the electrical characteristics of the generated AC signal) based on operating conditions. For example, the controller 140 may electrically communicate with various sensors deployed in the system 100 and receive measurement data from such sensors. For instance, the controller 140 may use temperature measurements (e.g., measured by a thermistor) to adjust the AC signal applied to the electrode 110 to maintain its temperature below a safe threshold (e.g., 41°C). This can be achieved, for example, by measuring the temperature of the electrode and controlling the AC signal generated by the AC voltage source 130 based on the measured temperature (e.g., adjusting the amplitude of the AC signal or pausing the application of the AC signal for a period of time).

[0053] exist Figure 1A In the depicted example, the electrodes are arranged such that one pair of electrodes 110 is positioned above region 104 and another pair of electrodes 110 is positioned below region 104. All electrodes within any given pair are electrically coupled to each other (and therefore will be at the same potential). The voltage applied by the AC voltage source 130 between the upper and lower electrodes 110 causes an electric field to be formed between the two sets of electrodes 110. The electrical characteristics (e.g., voltage level, frequency, duty cycle, waveform) of the AC signal generated by the AC voltage source 130 will form an associated electric field that, for a particular individual subject, blocks or alleviates the pain experienced by the subject. Thus, for example, the electrical characteristics of an AC voltage signal previously determined to be capable of blocking or alleviating the pain experienced by the subject (e.g., based on tests performed on a particular subject) can be used to set up a device for pain-blocking therapy, for example, for a particular individual subject. Alternatively, if the electrical characteristics of the AC voltage that would cause the electric field to form to block or alleviate the pain experienced by the subject are unknown, the electrodes can be... Figure 1A The configuration shown is the same (or different) configuration to be arranged, and the specific electrical properties that achieve the pain-blocking electric field are determined (e.g., in a way discussed below).

[0054] Device 100 can generate an AC signal with electrical characteristics previously determined for a specific individual based on testing performed on the subject (i.e., at an earlier time). In this case, controller 140 retrieves data associated with that specific individual (e.g., from local memory or from a remote server) specifying the voltage and frequency that the AC signal should be set to achieve pain blocking for the individual. Controller 140 (which may be part of AC voltage source 130) instructs the AC voltage source to generate a signal with a specified amplitude and frequency. The data retrieved for the subject may also optionally include information about the specific configuration / arrangement of electrodes that, when the AC signal (at a specific voltage and given frequency) is applied to the electrodes, will achieve a pain blocking effect on the pain experienced by the subject.

[0055] When the electrical properties of the AC signal that will block or alleviate pain in a given subject are unknown, device 100 can perform tests to determine those properties. In some embodiments, the test is performed immediately before the AC signal is applied to the subject using the same hardware that will ultimately be used to apply the pain-blocking AC signal. Alternatively, the test can be performed at any prior time (e.g., minutes, hours, days, weeks, or months ago) using the same hardware that will ultimately be used to apply the pain-blocking AC signal or using different hardware.

[0056] Once the test has been performed and the electrical characteristics have been established, pain management treatment can be administered to the subject. Optionally, the electrical characteristic values ​​determined by performing the test can be recorded (e.g., locally recorded in a memory device of controller 140 or recorded at a remote server). Furthermore, during subsequent pain management for a specific subject (typically for the same type of pain tested), the recorded electrical characteristics can be retrieved and used to configure AC voltage source 130. As noted above, the data recorded after performing the test may also include electrode information (e.g., the number and type of electrodes) and configuration information indicating how the electrodes are positioned on the subject's body.

[0057] Various methods can be used to determine the electrical properties of the AC signal applied to electrode 110 to achieve pain blocking or relief effects. In a first example method (also known as the amplitude scanning method), a test is performed on the subject to determine a threshold representing the minimum amplitude of an AC signal for a given frequency when the subject experiences an electrical sensation. For example, multiple electrodes are positioned at corresponding locations on the subject's body. Typically, the electrodes are placed near the part of the body where the subject is experiencing pain. In some cases, it is possible (depending on what can be used with...) Figure 1AElectrodes are placed in an arrangement similar to the one depicted, such that the target site 104 (the location where the subject is experiencing pain) is located between the electrodes 110, such that when an electric field is applied when the AC voltage source is activated, the electric field will pass through the target site. For example, at least one electrode of the electrodes 110 may be positioned proximally relative to the target site 104, and at least one electrode of the electrodes 110 may be positioned distally relative to the target site, such as... Figure 1A As depicted. In other cases, the electrodes can be positioned entirely proximally relative to the target site (meaning the electrodes will be positioned between the target site and the spinal cord). This type of arrangement may be necessary when it is difficult to place the target site between the electrodes, such as when the target site is at a joint (e.g., the elbow or wrist).

[0058] After the electrodes have been placed, a given frequency of the AC signal is set between 50 kHz and 1 MHz. The AC voltage source is set to an initial amplitude (typically low enough that it is unlikely to induce an electrosensory sensation in the subject) and activated. The voltage level is then gradually increased (e.g., by increasing the amplitude by predetermined steps over predetermined time periods). Eventually, after the amplitude level has been sufficiently increased, the subject will begin to experience an electrosensory sensation (e.g., manifested as a vibratory sensation, paresthesia, and / or a twitching or contraction of muscle fibers). The onset of the electrosensory sensation can be reported by the subject or detected using specialized sensors to monitor muscle behavior and determine the onset of the electrosensory sensation in the subject. Once an electrosensory sensation is experienced or detected, the amplitude of the AC signal is recorded and then used to represent a threshold (i.e., the minimum amplitude at which an AC signal at a given frequency induces an electrosensory sensation). Thus, in some embodiments, the controller 140 may be configured to control the operation of the AC voltage source during the testing of the subject, such that the AC voltage source (i) applies a test AC signal between the plurality of electrodes at a given frequency, and (ii) increases the amplitude of the test AC signal until the subject begins to experience an electrosensory sensation. The controller is also configured to record the amplitude of the test AC signal when the subject begins to experience electrosensory sensation, and to use the recorded amplitude as a threshold.

[0059] Once the threshold voltage is determined, the device can be configured to begin applying an AC signal to the electrodes on the subject's body at a given frequency (and / or other characteristics of the AC signal and device setup, such as electrode configuration) to block or alleviate pain at the target site. In some embodiments, once pain-blocking treatment begins (i.e., after the threshold is determined), the actual amplitude of the AC signal to be applied can be between 75% and 150% of the determined threshold voltage value. In other embodiments, the actual amplitude of the AC signal to be applied may be 25% to 150%, 25% to 120%, 25% to 100%, 25% to 99%, 33% to 150%, 33% to 120%, 33% to 100%, 33% to 99%, 40% to 150%, 40% to 120%, 40% to 100%, 40% to 99%, 50% to 150%, 50% to 120%, 50% to 100%, 50% to 99%, 60% to 150%, 60% to 120%, 60% to 100%, 60% to 99%, 70% to 150%, 70% to 120%, 70% to 100%, 70% to 99%, 80% to 150%, 80% to 120%, 80% to 100%, or 80% to 99% of the determined threshold voltage value.

[0060] In some embodiments, the AC signal is set to an amplitude between 100% and 120% of the threshold. And although this amplitude will induce an electrical sensation, many subjects will prefer a milder version of the electrical sensation rather than the pain they are trying to avoid.

[0061] For many subjects, the pain-blocking effect occurs *before* the electrosensory effect begins, i.e., before the determined threshold voltage value is reached. For these subjects, the amplitude of the AC signal can be set to 80% to 99% of the threshold, or to 25% to 99%, 25% to 99%, 33% to 99%, 40% to 99%, 50% to 99%, 60% to 99%, or 70% to 99% of the threshold. It should be noted that the lower limit of the percentage range providing the pain-blocking effect may vary from subject to subject. The selected percentage value may also depend on factors such as the severity of pain experienced by the subject, the desired duration of treatment, etc. Alternatively, the amplitude of the AC signal can be set to a default percentage of the threshold (e.g., between 80% and 99%), regardless of the presence of specific conditions or factors.

[0062] Another example method for determining the electrical characteristics of an AC signal is to determine the AC signal frequency that induces an electrosensory sensation in a subject for a specific AC signal amplitude level. It has been observed that when the AC signal frequency is decreased, there exists a point at which the electrosensory sensation begins. Therefore, the AC signal amplitude can be set to a specific amplitude level (e.g., between 50 and 150 VRMS or 20 and 150 VRMS), and the frequency at which the electrosensory sensation is triggered in the subject can then be determined. To determine this electrosensory triggering frequency, a plurality of electrodes (or electrode assemblies) are positioned on the subject (some predetermined electrode configuration may also be used here). A test AC signal is then applied between the plurality of electrodes, wherein the test AC signal is maintained at a specific amplitude. The frequency of the AC signal starts at an initial value and gradually decreases (e.g., decreasing by a predetermined step size and over a predetermined time period) until the subject begins to experience an electrosensory sensation (alternatively, a sensor may be used to detect the onset of the electrosensory sensation). Once the subject has experienced the electrosensory effect, the frequency at which the electrosensory effect begins is recorded, and the recorded frequency is used as the given frequency when the actual therapeutic application of the AC signal begins.

[0063] Therefore, in the latter method, the controller 140 can also be configured to control the operation of the AC voltage source during the test on the subject, such that the AC voltage source (i) applies a test AC signal between the plurality of electrodes, wherein the test AC signal is maintained at a specific amplitude, and (ii) decreases the frequency of the second AC signal until the subject begins to experience an electrical sensation. The controller 140 is additionally configured to record the frequency of the second AC signal when the subject begins to experience an electrical sensation, and use the recorded frequency as a given frequency. Here, the threshold corresponds to a specific amplitude of the test AC signal set at the start of the test.

[0064] Another approach to determining the electrical characteristics of an AC signal when used to block or relieve pain is a hybrid approach, where both the frequency and amplitude of the AC signal are varied. Figure 2 This includes a graph 200 illustrating the periodic frequency variation of AC voltage excitation. Figure 2 The frequency variation curve shown is used to compare with Figure 1A In an experiment using the same apparatus described, two pairs of ceramic discs 110 were placed on the subject's arm, approximately 6 cm apart. As shown in graph 200, the frequency curve of the AC signal operated at a fundamental frequency of 100 kHz, periodically shifting to 300 kHz every 200 ms and then back to 100 kHz. Each shift lasted 40 ms. As the frequency cycled in this manner, the amplitude increased from the initial voltage level until the subject felt an electrical sensation.

[0065] Experiments were conducted to verify that subjects experiencing electrical sensations did not feel pain. This was done by clamping the subject's arm with tweezers or a toothpick. In the specific experiment conducted, the subject reported tactile sensation but no pain.

[0066] Therefore, in this example, controller 140 is configured to decrease the frequency characteristics of the test AC signal from a maximum frequency to a minimum frequency during the first part of the periodic cycle, maintain the frequency of the second AC signal at a minimum frequency (e.g., 100 kHz) during the second part of the periodic cycle, and increase the frequency of the test AC signal to the maximum frequency during the third part of the periodic cycle. During the periodic cycle, the amplitude of the AC signal increases slowly (e.g., in steps of 0.5 V per periodic cycle).

[0067] In some embodiments, the AC voltage source (e.g., based on a control signal received from controller 140) is configured to apply an AC signal (e.g., a voltage determined according to the test method described above) as a pulse train sequence that may be periodic or aperiodic. For example, Figure 3 The plotted graph 300 illustrates the voltage level of an AC signal (at a given frequency) applied to a subject as a sequence of pulse trains. Figure 3 In the example depicted, a 30ms AC signal pulse train occurs every 200ms (resulting in a 15% duty cycle).

[0068] In some embodiments, the AC signal comprises a periodic sequence of AC pulse trains, wherein each pulse train has a duration of less than 50 ms. In some embodiments, the periodic sequence of pulse trains has a period between 100 ms and 2 seconds. It should be noted that the pulse train sequence can be time-constrained (e.g., 60 seconds to 300 seconds). Applying the pulse train sequence within a time-constrained period avoids generating excessive heat at the electrode site. In other embodiments (not shown), the pulse train sequence can be non-periodic. In these embodiments, the duration of some pulse trains or the duration of the corresponding period / interval of those pulse trains are not equal.

[0069] The pain-blocking effect of the alternating electric field can persist for a period of time after the AC signal is stopped being applied to the electrodes. Therefore, applying something like... Figure 3 The illustrated periodic waveform can achieve pain blocking while reducing the adverse effects of heat generation at the electrode site and / or reducing the overall effective duration of treatment for the subject (i.e., the overall duration of non-zero voltage applied to the electrode).

[0070] As noted above, in various embodiments, controller 140 can be configured to control the operation of AC voltage source 130 in response to changes in operating conditions, such as an increase in temperature. Therefore, the controller can be configured to adjust the pulse train sequence to, for example, increase the period (e.g., from 200 ms to 400 ms), shorten the pulse train size (e.g., from 50 ms to 30 ms), or shorten the sequence length if, for example, a sensor coupled to the electrodes indicates an increase in temperature. Controller 140 can also be configured to monitor other conditions (e.g., based on biometric measurements from a subject, or based on the operating conditions of device 100) and make necessary adjustments to the characteristics of the pulse train sequence.

[0071] As noted earlier, the amplitude and frequency of the AC signal used to block pain experienced by a particular subject can be determined based on a test performed on the subject, during which the frequency or amplitude (or both) of the AC signal generated by the AC voltage source 130 is scanned until the subject begins to experience an electrical sensation. These electrical characteristics can be determined for a specific arrangement of electrodes and for a specific selection of waveforms. That is, different electrode configurations (e.g., different numbers of electrodes, different types of electrodes, different positions of electrodes on the subject's body, different spatial arrangements, etc.) and / or different waveforms can cause the subject to begin experiencing an electrical sensation at different frequencies (for a specific amplitude level) or different amplitudes (for a given frequency).

[0072] Therefore, when identifying the amplitude and frequency to be used for pain blocking, the electrode configuration and waveform characteristics used to identify the amplitude and frequency of the AC signal can be recorded and documented. Subsequently, at a future point in time when the subject needs to undergo another pain blocking treatment, the electrode configuration previously used with the previously determined amplitude, frequency, and / or waveform can be replicated, except that the AC voltage source is set to generate an AC signal with the previously determined amplitude and frequency.

[0073] The methods discussed above are based on finding the appropriate electrical properties of the AC signal for a specific subject. Another method that can be used to treat pain in subjects is based on data regarding the use of the device 100 of Figure 1 on a subject population.

[0074] Such general performance information may include the number of subjects experiencing an electrosensory sensation at various combinations of amplitude and frequency (and optionally for a specific waveform and / or electrode configuration). Based on this data, electrical characteristics likely to trigger an electrosensory sensation in the majority of subjects can be determined. For example, a value at which 80% of subjects experience an electrosensory sensation at a given frequency can be determined. This value can then be used as the threshold discussed above. Optionally, if data considering the demographic characteristics of the subjects (e.g., sex, age, height, weight, etc.) is available, the AC signal can be characterized based on a more limited dataset corresponding to a group of subjects matched with those being treated.

[0075] Another method that can be used to administer pain-blocking therapy to subjects is to have device 100 apply a predetermined voltage threshold, such as a peak-to-peak value between 20 volts and 100 volts, to all subjects. For example, device 100 can apply predetermined voltage thresholds of 20 volts to 25 volts, 25 volts to 30 volts, 30 volts to 40 volts, 40 volts to 50 volts, 50 volts to 60 volts, 60 volts to 70 volts, 70 volts to 80 volts, 80 volts to 90 volts, 90 volts to 100 volts, 30 volts to 60 volts, 30 volts to 90 volts, 40 volts to 80 volts, 40 volts to 90 volts, or 45 volts to 90 volts to all subjects. Device 100 was tested on a limited number of volunteers, and it was found that peak-to-peak values ​​of 30V to 60V, 40V to 80V, and 45V to 90V provided significant pain-blocking effects for each test subject.

[0076] While the various pain-blocking methods described herein are discussed in terms of the subject's electrosensory perception (to determine the appropriate AC electrical characteristic values ​​for pain blocking), in some embodiments, other physiological effects may be used as a means of determining the AC signal characteristics for pain blocking. One example of such a physiological effect is the occurrence of action potential activity. During certain types of electrical stimulation of biological tissue, an electrically evoked compound action potential (ECAP) represents the approximately synchronous firing of a group of electrically stimulated nerve fibers. When an electrical signal of sufficient energy is applied to activate nerve fibers, fibers of different diameters and locations are activated at approximately the same time (e.g., within fractions of a millisecond), and their action potentials (APs) propagate to the vicinity of the recording electrodes at different speeds. Furthermore, different nerve fibers of different diameters have different activation thresholds and conduction velocities, transmitting different signals, such as sensory signals (vibration, temperature, hair movement, muscle contraction, joint position, etc.).

[0077] An electric field-generating electrode associated with electrosensory perception (ECAP) can be measured using a set of electrodes placed on the subject's skin. These electrodes detect the composite sum of individual acute pressure points (APs) arriving approximately simultaneously, which is displayed as a curve for a given amplitude and duration. The ECAP measuring electrodes can be positioned on electric field-generating electrodes used to block pain (e.g., [insert electrode name here]). Figure 1A The passive electrode (used for detecting electrical activity) can be placed near electrode 110. Figure 1A The upper electrode 110 is positioned near the lower electrode 110, while another passive electrode may be placed near the lower electrode 110. Signals from the ECAP measuring electrodes (which may be on the order of mV, for example) are forwarded to the ECAP measuring system (not shown). The ECAP measuring system (e.g., using an amplifier and an analog-to-digital converter) processes these signals. The processed signals can then be used to determine the likelihood that the subject is experiencing electrosensory sensation and / or is approaching a threshold expected to exceed electrosensory sensation. This determination may be based on a lookup table that indicates the likelihood of electrosensory sensation based on the detection values ​​of ECAP activity, thereby using a machine learning system to predict the likelihood of electrosensory sensation, or using any other method that correlates ECAP activity with the onset of electrosensory sensation. Further details about ECAP and its measurement are provided, for example, in US 2023 / 0414955 entitled “Closed-Loop Technique to Reduce Electrosensory While Treating a Subject Using Alternating Electric Fields,” the full text of which is incorporated herein by reference.

[0078] ECAP measurements can be combined with the amplitude scanning or frequency scanning methods described above. For example, in the amplitude scanning method, the AC signal is set to a given frequency (e.g., between 100 kHz and 500 kHz), and the amplitude is set to an initial value and gradually increased. During the amplitude scan, ECAP measuring electrodes deployed near the pain-blocking electrodes passively measure electrical activity and forward the measurement results to controller 140. Controller 140 determines whether an electrosensory sensation has been triggered or is about to be triggered based on the received measurements. Once controller 140 determines that an electrosensory sensation has been triggered or is about to be triggered, it records the value of the gradually increasing amplitude of the AC signal. The recorded value represents a threshold upon which the electrical characteristics of the pain-blocking AC signal are set.

[0079] Figure 4This is a flowchart of an example procedure 400 for blocking pain experienced by a subject at a target site on the subject's body. The procedure includes (at S410) positioning multiple electrodes at corresponding locations on the subject's body and (at S420) applying a first AC signal between the multiple electrodes. In procedure 400, the corresponding locations are selected such that when the first AC signal is applied between the multiple electrodes, the first AC signal will block pain at the target site. Furthermore, the amplitude and frequency characteristics of the first AC signal are such that when the first AC signal is applied between the multiple electrodes, the first AC signal will block pain at the target site. Additionally, the first AC signal has a given frequency between 50 kHz and 1 MHz, and an amplitude between 75% and 150% of a threshold, which is determined (a) based on a test performed on the subject to determine the minimum amplitude at which the subject experiences an electrical sensation at that given frequency; or (b) based on previously obtained data specifying the minimum amplitude at which most subjects experience an electrical sensation at that given frequency.

[0080] In some embodiments, the threshold is determined prior to application by: applying a second AC signal (also referred to as a "test AC signal") to the subject's body at the given frequency; increasing the amplitude of the second AC signal until the subject begins to experience an electric sensation; recording the amplitude of the second AC signal when the subject begins to experience an electric sensation; and using the recorded amplitude as the threshold. In some embodiments, the first AC signal has an amplitude between 80% and 99% of the threshold. In other embodiments, the first AC signal has an amplitude between 100% and 120% of the threshold.

[0081] In some embodiments, a test is performed to find the frequency that triggers an electrical sensation in the subject. In such embodiments, the given frequency is determined before application by: applying a second AC signal to the subject's body, wherein the second AC signal is maintained at a specific amplitude; decreasing the frequency of the second AC signal until the subject begins to experience an electrical sensation; recording the frequency of the second AC signal when the subject begins to experience an electrical sensation; and using the recorded frequency as the given frequency. In these embodiments, the threshold will be the specific amplitude of the second AC signal.

[0082] In some embodiments, a test is performed to find a combination of amplitude and frequency that triggers an electrosensory sensation in the subject. In such embodiments, prior to this application, a given frequency and threshold are determined by applying a second AC signal to the subject's body, varying the frequency of the second AC signal according to a periodic frequency variation curve, and increasing the amplitude of the second AC signal while varying its frequency. When it is detected that the subject has begun to experience an electrosensory sensation, the frequency and amplitude of the second AC signal at the time the subject begins to experience the sensation are recorded, and the recorded frequency is used as the given frequency, and the recorded amplitude is used as the threshold. In some embodiments, the periodic frequency variation curve may cause the frequency characteristics of the second AC signal to decrease from a maximum frequency to a minimum frequency during a first portion of a single periodic operating cycle, maintain the frequency of the second AC signal at the minimum frequency during a second portion of the periodic cycle, and increase the frequency of the second AC signal to the maximum frequency during a third portion of the periodic cycle.

[0083] In some embodiments, the positions of the plurality of electrodes are selected such that the target region is located between the plurality of electrodes. In other embodiments, the plurality of electrodes are positioned proximally relative to the target region. In some embodiments, the first AC signal has a frequency between 90 kHz and 300 kHz.

[0084] In some embodiments, the first AC signal comprises a periodic sequence of pulses of AC voltage, wherein each pulse has a duration of less than 50 ms, and the periodic sequence has a period between 100 ms and 2 seconds. In some embodiments, the first AC signal comprises a sequence of pulses of AC voltage, wherein each pulse has a duration of less than 50 ms, and wherein consecutive pulses within the sequence are spaced 100 ms to 2 seconds apart. In some embodiments, the threshold is based on previously obtained data specifying the minimum amplitude at which at least 80% of subjects experience an electrosensory sensation at a given frequency.

[0085] The headings are provided for convenience only and should not be construed as limiting the invention in any way. Embodiments shown under any heading or section of this disclosure may be combined with embodiments shown under the same or any other heading or section of this disclosure. Unless otherwise indicated herein or clearly contradicted by the context, the invention covers any combination of the elements described herein in all possible variations.

[0086] While the invention has been disclosed with reference to certain embodiments, various modifications, alterations, and changes can be made to the described embodiments without departing from the scope and domain of the invention as defined by the appended claims. Therefore, the invention is intended to be limited to the described embodiments, but rather to have the full scope defined by the language of the appended claims and their equivalents.

Claims

1. A method for blocking pain experienced by a subject at a target site on the subject's body, the method comprising: Multiple electrodes are positioned at corresponding locations on the subject's body; as well as A first AC signal is applied between the plurality of electrodes. The corresponding location is selected such that when the first AC signal is applied between the plurality of electrodes, the first AC signal will block pain at the target site. The amplitude and frequency characteristics of the first AC signal are such that when the first AC signal is applied between the plurality of electrodes, the first AC signal will block pain at the target site, and The first AC signal has a given frequency between 50 kHz and 1 MHz.

2. The method according to claim 1, wherein the first AC signal has an amplitude of at least 30V peak-to-peak value.

3. The method according to claim 1, wherein the first AC signal has an amplitude of 30V to 90V peak-to-peak value.

4. The method of claim 1, wherein the amplitude of the first AC signal is set to at least 25% of a threshold, and The threshold is determined based on a test performed on the subject to find the lowest amplitude of electrical sensation experienced by the subject at the given frequency.

5. The method of claim 1, wherein the amplitude of the first AC signal is set to 50% to 100% of a threshold, and The threshold is determined based on a test performed on the subject to find the lowest amplitude of electrical sensation experienced by the subject at the given frequency.

6. The method according to claim 5, wherein, The threshold is determined by the following steps before the application is performed: A second AC signal is applied to the subject's body at the given frequency; Increase the amplitude of the second AC signal until the subject begins to experience an electrical sensation; Record the amplitude of the second AC signal when the subject begins to experience an electrical sensation; as well as The recorded amplitude is used as the threshold.

7. The method of claim 6, wherein after the positioning is performed using the plurality of electrodes, the second AC signal is applied to the subject's body.

8. The method of claim 5, wherein the first AC signal has an amplitude between 80% and 99% of the threshold.

9. The method according to claim 1, wherein, The given frequency is determined by the following steps before the application is performed: A second AC signal is applied to the subject's body, wherein the second AC signal is maintained at a specific amplitude; Reduce the frequency of the second AC signal until the subject begins to experience an electrical sensation; Record the frequency of the second AC signal when the subject begins to experience an electrical sensation; and The recorded frequency is used as the given frequency.

10. The method of claim 9, wherein after the positioning is performed using the plurality of electrodes, the second AC signal is applied to the subject's body.

11. The method of claim 1, wherein the positions in which the plurality of electrodes are positioned are selected such that the target portion is located between the plurality of electrodes.

12. The method of claim 1, wherein the plurality of electrodes are positioned proximally relative to the target region.

13. The method of claim 1, wherein at least one of the electrodes is positioned proximally relative to the target region, and at least one of the electrodes is positioned distally relative to the target region.

14. The method of claim 1, wherein the first AC signal has a frequency between 90 kHz and 300 kHz.

15. A device for blocking pain experienced by a subject at a target site on the subject's body, the device comprising: An AC voltage source, configured to generate a first AC signal; and A controller configured to control the operation of the AC voltage source such that (a) the amplitude and frequency characteristics of the first AC signal are such that when the first AC signal is applied between multiple electrodes positioned at corresponding locations on the subject's body, the first AC signal will block pain at the target site; (b) the first AC signal has a given frequency between 50 kHz and 1 MHz; and (c) the first AC signal has an amplitude between 50% and 100% of a threshold. The threshold is determined based on a test performed on the subject to find the lowest amplitude of electrical sensation experienced by the subject at the given frequency.

16. The apparatus of claim 15, wherein the controller is further configured to perform the test by: (a) Controlling the operation of the AC voltage source such that the AC voltage source (i) applies a second AC signal to the subject's body at the given frequency, and (ii) increases the amplitude of the second AC signal until the subject begins to experience an electrical sensation. (b) Record the amplitude of the second AC signal when the subject begins to experience an electrical sensation, and (c) Use the recorded amplitude as the threshold.

17. The apparatus of claim 16, wherein the amplitude of the first AC signal is set between 80% and 99% of the threshold.

18. The apparatus of claim 15, wherein the first AC signal has a frequency between 90 kHz and 300 kHz.

19. The apparatus of claim 15, wherein the first AC signal comprises a sequence of pulse trains of AC voltage, wherein each pulse train has a duration of less than 50 ms, and wherein the consecutive pulse trains within the sequence are spaced 100 ms to 2 seconds apart.

20. The apparatus of claim 15, wherein the controller is further configured to perform the test by: (a) Controlling the operation of the AC voltage source during the test on the subject, such that the AC voltage source (i) applies a second AC signal to the subject's body, wherein the second AC signal is maintained at a specific amplitude, and (ii) reduces the frequency of the second AC signal until the subject begins to experience an electrical sensation. (b) Record the frequency of the second AC signal when the subject begins to experience an electrical sensation, and (c) Use the recorded frequency as the given frequency. The threshold corresponds to the specific amplitude of the second AC signal.

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