Patent Publication Number: US-10780276-B1

Title: Systems and methods for selecting low-power, effective signal delivery parameters for an implanted pulse generator

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     The present application is a continuation of U.S. patent application Ser. No. 15/346,432, filed Nov. 8, 2016, which is a continuation of U.S. patent application Ser. No. 15/057,913, now issued as U.S. Pat. No. 9,517,344, filed Mar. 1, 2016, which is a continuation of U.S. patent application Ser. No. 14/657,971, filed Mar. 13, 2015, which is incorporated herein by reference in its entirety. 
    
    
     TECHNICAL FIELD 
     The present disclosure is directed to systems and methods for selecting low-power, effective signal delivery parameters for an implanted pulse generator. In particular applications, the techniques disclosed herein are applied in the context of delivering high-frequency, paresthesia-free therapy signals. 
     BACKGROUND 
     Neurological stimulators have been developed to treat pain, movement disorders, functional disorders, spasticity, cancer, cardiac disorders, and various other medical conditions. Implantable neurological stimulation systems generally have an implantable signal generator and one or more leads that deliver electrical pulses to neurological tissue or muscle tissue. For example, several neurological stimulation systems for spinal cord stimulation (SCS) have cylindrical leads that include a lead body with a circular cross-sectional shape and one or more conductive rings (i.e., contacts) spaced apart from each other at the distal end of the lead body. The conductive rings operate as individual electrodes and, in many cases, the SCS leads are implanted percutaneously through a needle inserted into the epidural space, with or without the assistance of a stylet. 
     Once implanted, the signal generator applies electrical pulses to the electrodes, which in turn modify the function of the patient&#39;s nervous system, such as by altering the patient&#39;s responsiveness to sensory stimuli and/or altering the patient&#39;s motor-circuit output. In SCS therapy for the treatment of pain, the signal generator applies electrical pulses to the spinal cord via the electrodes. In conventional SCS therapy, electrical pulses are used to generate sensations (known as paresthesia) that mask or otherwise alter the patient&#39;s sensation of pain. For example, in many cases, patients report paresthesia as a tingling sensation that is perceived as less uncomfortable than the underlying pain sensation. 
     In contrast to traditional or conventional (i.e., paresthesia-based) SCS, a form of paresthesia-free SCS has been developed that uses therapy signal parameters that treat the patient&#39;s sensation of pain without generating paresthesia or otherwise using paresthesia to mask the patient&#39;s sensation of pain. One of several advantages of paresthesia-free SCS therapy systems is that they eliminate the need for uncomfortable paresthesias, which many patients find objectionable. However, a challenge with paresthesia-free SCS therapy systems is that the signal may be delivered at frequencies, amplitudes, and/or pulse widths that use more power than conventional SCS systems. As a result, there is a need to develop optimized systems and methods for effectively delivering therapy while efficiently using power resources. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  is a partially schematic illustration of an implantable spinal cord modulation system positioned at the spine to deliver therapeutic signals in accordance with several embodiments in the present technology. 
         FIG. 1B  is a partially schematic, cross-sectional illustration of a patient&#39;s spine, illustrating representative locations for implanted lead bodies in accordance with embodiments of the present technology. 
         FIG. 2  is a flow diagram illustrating a process for selecting signal delivery parameters in accordance with an embodiment of the present technology. 
         FIG. 3  is a flow diagram illustrating a representative process for selecting signal delivery parameters in accordance with another embodiment of the present technology. 
     
    
    
     DETAILED DESCRIPTION 
     General aspects of the environments in which the disclosed technology operates are described below under Heading 1.0 (“Overview”) with reference to  FIGS. 1A and 1B . Particular embodiments of the technology are described further under Heading 2.0 (“Representative Embodiments”) with reference to  FIGS. 2 and 3 . Additional embodiments are described under Heading 3.0 (“Additional Embodiments”). 
     1.0 Overview 
     One example of a paresthesia-free SCS therapy system is a “high frequency” SCS system. High frequency SCS systems can inhibit, reduce, and/or eliminate pain via waveforms with high frequency elements or components (e.g., portions having high fundamental frequencies), generally with reduced or eliminated side effects. Such side effects can include unwanted paresthesia, unwanted motor stimulation or blocking, unwanted pain or discomfort, and/or interference with sensory functions other than the targeted pain. In a representative embodiment, a patient may receive high frequency therapeutic signals with at least a portion of the therapy signal at a frequency of from about 1.5 kHz to about 100 kHz, or from about 1.5 kHz to about 50 kHz, or from about 3 kHz to about 20 kHz, or from about 5 kHz to about 15 kHz, or at frequencies of about 8 kHz, 9 kHz, or 10 kHz. These frequencies are significantly higher than the frequencies associated with conventional “low frequency” SCS, which are generally below 1,200 Hz, and more commonly below 100 Hz. Accordingly, modulation at these and other representative frequencies (e.g., from about 1.5 kHz to about 100 kHz) is occasionally referred to herein as “high frequency stimulation,” “high frequency SCS,” and/or “high frequency modulation.” Further examples of paresthesia-free SCS systems are described in U.S. Patent Publication Nos. 2009/0204173 and 2010/0274314, the respective disclosures of which are herein incorporated by reference in their entireties. 
       FIG. 1A  schematically illustrates a representative patient therapy system  100  for providing relief from chronic pain and/or other conditions, arranged relative to the general anatomy of a patient&#39;s spinal column  191 . The system  100  can include a signal generator  101  (e.g., an implanted or implantable pulse generator or IPG), which may be implanted subcutaneously within a patient  190  and coupled to one or more signal delivery elements or devices  110 . The signal delivery elements or devices  110  may be implanted within the patient  190 , typically at or near the patient&#39;s spinal cord midline  189 . The signal delivery elements  110  carry features for delivering therapy to the patient  190  after implantation. As shown, the signal generator  101  can be implanted within the patient. In such an embodiment, the signal generator  101  can be connected directly to the signal delivery devices  110 , or it can be coupled to the signal delivery devices  110  via a signal link or lead extension  102 . In an embodiment wherein the signal generator is external to the patient, the signal generator can deliver a signal to the signal delivery device  110  via a wireless link, such as RF communication. In a further representative embodiment, the signal delivery devices  110  can include one or more elongated lead(s) or lead body or bodies  111  (identified individually as a first lead  111   a  and a second lead  111   b ). As used herein, the terms signal delivery device, lead, and/or lead body include any of a number of suitable substrates and/or support members that carry electrodes/devices for providing therapy signals to the patient  190 . For example, the lead or leads  111  can include one or more electrodes or electrical contacts that direct electrical signals into the patient&#39;s tissue, e.g., to provide for therapeutic relief. In other embodiments, the signal delivery elements  110  can include structures other than a lead body (e.g., a paddle) that also direct electrical signals and/or other types of signals to the patient  190 . 
     In a representative embodiment, one signal delivery device may be implanted on one side of the spinal cord midline  189 , and a second signal delivery device may be implanted on the other side of the spinal cord midline  189 . For example, the first and second leads  111   a ,  111   b  shown in  FIG. 1A  may be positioned just off the spinal cord midline  189  (e.g., about 1 mm offset) in opposing lateral directions so that the two leads  111   a ,  111   b  are spaced apart from each other by about 2 mm. In particular embodiments, the leads  111  may be implanted at a vertebral level ranging from, for example, about T 8  to about T 12 . In other embodiments, one or more signal delivery devices can be implanted at other vertebral levels, e.g., as disclosed in U.S. Patent Application Publication No. 2013/0066411, which is incorporated herein by reference in its entirety. 
     The signal generator  101  can transmit signals (e.g., electrical signals) to the signal delivery elements  110  that up-regulate (e.g., excite) and/or down-regulate (e.g., block or suppress) target nerves. As used herein, and unless otherwise noted, the terms “modulate,” “modulation,” “stimulate,” and “stimulation” refer generally to signals that have either type of the foregoing effects on the target nerves. The signal generator  101  can include a machine-readable (e.g., computer-readable) or controller-readable medium containing instructions for generating and transmitting suitable therapy signals. The signal generator  101  and/or other elements of the system  100  can include one or more processor(s)  107 , memory unit(s)  108 , and/or input/output device(s)  112 . Accordingly, the process of providing modulation signals, providing guidance information for positioning the signal delivery devices  110 , establishing battery charging and/or discharging parameters, establishing signal delivery parameters, and/or executing other associated functions can be performed by computer-executable instructions contained by, on or in computer-readable media located at the pulse generator  101  and/or other system components. Further, the pulse generator  101  and/or other system components may include dedicated hardware, firmware, and/or software for executing computer-executable instructions that, when executed, perform any one or more methods, processes, and/or sub-processes described herein; e.g., the methods, processes, and/or sub-processes described with reference to  FIGS. 2-3  below. The dedicated hardware, firmware, and/or software also serve as “means for” performing the methods, processes, and/or sub-processes described herein. The signal generator  101  can also include multiple portions, elements, and/or subsystems (e.g., for directing signals in accordance with multiple signal delivery parameters), carried in a single housing, as shown in  FIG. 1A , or in multiple housings. 
     The signal generator  101  can also receive and respond to an input signal received from one or more sources. The input signals can direct or influence the manner in which the therapy, charging, parameter selection and/or other process instructions are selected, executed, updated, and/or otherwise performed. The input signals can be received from one or more sensors (e.g., an input device  112  shown schematically in  FIG. 1A  for purposes of illustration) that are carried by the signal generator  101  and/or distributed outside the signal generator  101  (e.g., at other patient locations) while still communicating with the signal generator  101 . The sensors and/or other input devices  112  can provide inputs that depend on or reflect patient state (e.g., patient position, patient posture, and/or patient activity level), and/or inputs that are patient-independent (e.g., time). Still further details are included in U.S. Pat. No. 8,355,797, incorporated herein by reference in its entirety. 
     In some embodiments, the signal generator  101  and/or signal delivery devices  110  can obtain power to generate the therapy signals from an external power source  103 . In one embodiment, for example, the external power source  103  can by-pass an implanted signal generator and generate a therapy signal directly at the signal delivery devices  110  (or via signal relay components). The external power source  103  can transmit power to the implanted signal generator  101  and/or directly to the signal delivery devices  110  using electromagnetic induction (e.g., RF signals). For example, the external power source  103  can include an external coil  104  that communicates with a corresponding internal coil (not shown) within the implantable signal generator  101 , signal delivery devices  110 , and/or a power relay component (not shown). The external power source  103  can be portable for ease of use. 
     In another embodiment, the signal generator  101  can obtain the power to generate therapy signals from an internal power source, in addition to or in lieu of the external power source  103 . For example, the implanted signal generator  101  can include a non-rechargeable battery or a rechargeable battery to provide such power. When the internal power source includes a rechargeable battery, the external power source  103  can be used to recharge the battery. The external power source  103  can in turn be recharged from a suitable power source (e.g., conventional wall power). 
     During at least some procedures, an external stimulator or trial modulator  105  can be coupled to the signal delivery elements  110  during an initial procedure, prior to implanting the signal generator  101 . For example, a practitioner (e.g., a physician and/or a company representative) can use the trial modulator  105  to vary the modulation parameters provided to the signal delivery elements  110  in real time, and select optimal or particularly efficacious parameters. These parameters can include the location from which the electrical signals are emitted, as well as the characteristics of the electrical signals provided to the signal delivery devices  110 . In some embodiments, input is collected via the external stimulator or trial modulator and can be used by the clinician to help determine what parameters to vary. In a typical process, the practitioner uses a cable assembly  120  to temporarily connect the trial modulator  105  to the signal delivery device  110 . The practitioner can test the efficacy of the signal delivery devices  110  in an initial position. The practitioner can then disconnect the cable assembly  120  (e.g., at a connector  122 ), reposition the signal delivery devices  110 , and reapply the electrical signals. This process can be performed iteratively until the practitioner obtains the desired position for the signal delivery devices  110 . Optionally, the practitioner may move the partially implanted signal delivery devices  110  without disconnecting the cable assembly  120 . Furthermore, in some embodiments, the iterative process of repositioning the signal delivery devices  110  and/or varying the therapy parameters may not be performed. 
     The signal generator  101 , the lead extension  102 , the trial modulator  105  and/or the connector  122  can each include a receiving element  109 . Accordingly, the receiving elements  109  can be patient implantable elements, or the receiving elements  109  can be integral with an external patient treatment element, device or component (e.g., the trial modulator  105  and/or the connector  122 ). The receiving elements  109  can be configured to facilitate a simple coupling and decoupling procedure between the signal delivery devices  110 , the lead extension  102 , the pulse generator  101 , the trial modulator  105  and/or the connector  122 . The receiving elements  109  can be at least generally similar in structure and function to those described in U.S. Patent Application Publication No. 2011/0071593, incorporated by reference herein in its entirety. 
     After the signal delivery elements  110  are implanted, the patient  190  can receive therapy via signals generated by the trial modulator  105 , generally for a limited period of time. During this time, the patient wears the cable assembly  120  and the trial modulator  105  outside the body. Assuming the trial therapy is effective or shows the promise of being effective, the practitioner then replaces the trial modulator  105  with the implanted signal generator  101 , and programs the signal generator  101  with therapy programs selected based on the experience gained during the trial period. Optionally, the practitioner can also replace the signal delivery elements  110 . Once the implantable signal generator  101  has been positioned within the patient  190 , the therapy programs provided by the signal generator  101  can still be updated remotely via a wireless physician&#39;s programmer (e.g., a physician&#39;s laptop, a physician&#39;s remote or remote device, etc.)  117  and/or a wireless patient programmer  106  (e.g., a patient&#39;s laptop, patient&#39;s remote or remote device, etc.). Generally, the patient  190  has control over fewer parameters than does the practitioner. For example, the capability of the patient programmer  106  may be limited to starting and/or stopping the signal generator  101 , and/or adjusting the signal amplitude. The patient programmer  106  may be configured to accept pain relief input as well as other variables, such as medication use. 
     In any of the foregoing embodiments, the parameters in accordance with which the signal generator  101  provides signals can be adjusted during portions of the therapy regimen. For example, the frequency, amplitude, pulse width, and/or signal delivery location can be adjusted in accordance with a pre-set therapy program, patient and/or physician inputs, and/or in a random or pseudorandom manner. Such parameter variations can be used to address a number of potential clinical situations. Certain aspects of the foregoing systems and methods may be simplified or eliminated in particular embodiments of the present disclosure. Further aspects of these and other expected beneficial results are detailed in U.S. Patent Application Publication Nos. 2010/0274314; 2009/0204173; and 2013/0066411 (all previously incorporated by reference) and U.S. Patent Application Publication No. 2010/0274317, which is incorporated herein by reference in its entirety. 
       FIG. 1B  is a cross-sectional illustration of the spinal cord  191  and an adjacent vertebra  195  (based generally on information from Crossman and Neary, “Neuroanatomy,” 1995 (published by Churchill Livingstone)), along with multiple leads  111  (shown as leads  111   a - 111   e ) implanted at representative locations. For purposes of illustration, multiple leads  111  are shown in  FIG. 1B  implanted in a single patient. In actual use, any given patient will likely receive fewer than all the leads  111  shown in  FIG. 1B . 
     The spinal cord  191  is situated within a vertebral foramen  188 , between a ventrally located ventral body  196  and a dorsally located transverse process  198  and spinous process  197 . Arrows V and D identify the ventral and dorsal directions, respectively. The spinal cord  191  itself is located within the dura mater  199 , which also surrounds portions of the nerves exiting the spinal cord  191 , including the ventral roots  192 , dorsal roots  193  and dorsal root ganglia  194 . The dorsal roots  193  enter the spinal cord  191  at the dorsal root entry zone  187 , and communicate with dorsal horn neurons located at the dorsal horn  186 . In one embodiment, the first and second leads  111   a ,  111   b  are positioned just off the spinal cord midline  189  (e.g., about 1 mm. offset) in opposing lateral directions so that the two leads  111   a ,  111   b  are spaced apart from each other by about 2 mm, as discussed above. In other embodiments, a lead or pairs of leads can be positioned at other locations, e.g., toward the outer edge of the dorsal root entry zone  187  as shown by a third lead  111   c , or at the dorsal root ganglia  194 , as shown by a fourth lead  111   d , or approximately at the spinal cord midline  189 , as shown by a fifth lead  111   e.    
     2.0 Representative Embodiments 
     Systems of the type described above with reference to  FIGS. 1A-1B  can include implanted pulse generators (IPGs) having rechargeable batteries or other rechargeable power sources that are periodically recharged with an external charger. In addition, such devices are configured to generate therapy signals, typically at higher frequencies than are used for conventional SCS, to produce pain relief without generating paresthesia in the patient. High frequency signals, however, may consume more energy than low frequency signals, e.g., for a given therapy, and may accordingly deplete the rechargeable power source more rapidly than conventional SCS therapy signals do. As a result, the patient may be required to recharge the implantable device more often than would be required for a conventional SCS device. Techniques in accordance with the present technology, described further below, can allow the system to automatically determine signal parameters that produce effective pain treatment with reduced (e.g., minimal) energy consumption. 
     In particular embodiments, embodiments of the therapy disclosed herein do not produce paresthesia or other undesirable side effects. This characteristic can significantly improve the degree to which the process for selecting the signal delivery parameters can be automated. In particular, with standard, conventional, low frequency SCS, the therapeutic efficacy (e.g., the degree of pain relief) typically increases with the amplitude of the signal. The power required to produce the signal also increases with amplitude. However, as the amplitude increases, other side effects, such as motor reflex and/or an overwhelming sensory intensity, overshadow the beneficial pain relief results. Accordingly, the approach for maximizing pain relief via conventional low frequency SCS therapy is typically to increase the amplitude of the signal until the patient can no longer tolerate the side effects. This can be a time-consuming operation, because the practitioner wishes to avoid over-stimulating the patient. It also tends to result in a therapy signal that requires a large amount of power, due to the high amplitude. Still further, this process is typically not automated, so as to avoid inadvertently over-stimulating the patient as the amplitude is increased. 
     By contrast, it has been discovered that the therapeutic efficacy (e.g., level of pain relief) produced by a high frequency signal may begin to decrease at higher amplitudes, before other sensory or motor side-effects appear to limit further increases in amplitude. Because the therapeutic efficacy level is expected to decrease before the onset of unwanted motor or sensory effects, the presently disclosed systems and methods can automatically increment and/or decrement the stimulation amplitude, within pre-selected ranges (e.g., efficacy ranges), without triggering unwanted side effects. This technique can be used to identify an amplitude at one or more frequencies that both produces effective therapy, and does so at a relatively low energy consumption rate (e.g., power). Further details are described below. 
       FIG. 2  is a flow diagram illustrating a representative process  200  for selecting a therapy signal for delivery to a patient in accordance with an embodiment of the present technology. Process portion  201  includes configuring a signal generator to deliver therapy signals at multiple combinations of parameters. The parameters can include combinations of amplitudes and frequencies in particular embodiments. In other embodiments, the parameters can include other characteristics of the therapy signal, for example, the duty cycle, pulse width, and/or interpulse interval. In any of these embodiments, process portion  203  includes determining the patient&#39;s response to individual combinations (e.g., each combination) of applied signal parameters. The patient&#39;s response can be measured using any of a variety of suitable techniques that have been developed for identifying the patient&#39;s level of pain. Such techniques include using VAS scores, NRS scores, Likert satisfaction scales, Oswestry disability indices, among others. These techniques can be used to provide a patient-specific but quantifiable measure of the efficacy of the therapy, which is expected to change as the signal delivery parameters change. The foregoing techniques include feedback from the patient via deliberate patient participation (e.g., the patient consciously writing, describing or keying in a pain score). In other embodiments, the patient&#39;s response may be determined without this level of patient participation, e.g., by directly measuring patient physiological values that are correlated with the patient&#39;s pain level. 
     Process portion  205  includes determining the expected energy consumption for individual combinations (e.g., each combination) of signals applied to the patient. For example, process portion  205  can include integrating the area under a wave form graph of amplitude as a function of time. Accordingly, signals with high amplitudes and high frequencies consume more power than signals with low amplitudes and low frequencies. However, in particular embodiments, signals with high frequencies but low amplitudes can consume more power than signals with low frequencies and high amplitudes, and vice versa. The level of computation used to determine whether a particular combination of signal delivery parameters consumes more energy than another can vary in complexity, as will be described in further detail later. 
     Process portion  207  includes delivering one or more therapy signals for additional therapy based on (a) the patient&#39;s responses to the signals (i.e., the therapeutic efficacy of the signals) and (b) the expected energy consumption associated with the signals. The manner in which these two characteristics are weighted can vary from one patient to another. For example, some patients may value high efficacy (e.g., highly effective pain relief) more than low power consumption. Such patients will accordingly be willing to recharge their implanted devices more frequently in order to obtain better pain relief. Other patients, on the other hand, may be willing to tolerate an increase (e.g., a slight increase) in pain in order to reduce the frequency with which they recharge their implanted devices. Process portion  207  can include accounting for (e.g., weighting) patient-specific preferences in order to identify one or more therapy signals or sets of therapy signal delivery parameters that satisfy the patient&#39;s requirements. 
       FIG. 3  is a detailed flow diagram illustrating a representative process  300  for selecting signal delivery parameters in accordance with another embodiment of the present technology. In a particular aspect of the illustrated embodiment, it is assumed or determined that other stimulation parameters (such as pulse width and the locations of active contacts, but excluding amplitude) are fixed, e.g., because they provide reasonable efficacy for the patient. The process  300  can include selecting a starting frequency (process portion  301 ), and selecting a frequency increment or list of frequencies (process portion  303 ). For example, process portion  301  can include selecting 10 kHz as a starting frequency and process portion  303  can include selecting a list of frequencies that includes 10 kHz and 1.5 kHz. In this simple example, just these two frequencies will be tested, at a variety of signal delivery amplitudes. In other cases, the list of frequencies can include more values (e.g., 10 kHz, 5 kHz, and 1.5 kHz). In still further embodiments, a frequency increment can be used, e.g., in lieu of a list of frequencies. For example, the frequency increment can be 1 kHz, so that multiple frequencies, spaced apart from each other by the 1 kHz increment, can be tested over the course of the process. Accordingly, the process can allow the practitioner, manufacturer, and/or other professional to select the number of frequencies tested, the values of the frequencies, and the manner in which the frequencies are selected in different ways for different patients. 
     In process portion  305 , the process  300  includes selecting an amplitude increment. The amplitude increment can be selected to allow the process to cover a suitably wide range of amplitudes within a reasonable period of time. It has been observed that the efficacy of particular high frequency therapy signals may take some time to develop. This is unlike the case for standard, low frequency SCS treatments, during which the patient can immediately identify whether or not the paresthesia associated with a particular therapy signal masks or overlies the pain. Instead, the effects of high frequency signals, or changes in high frequency signals, may take several hours to a day or so for the patient to detect. Accordingly, the amplitude increment can be selected by the practitioner to allow a reasonable number of different amplitudes to be tested over a reasonable period of time. For example, the practitioner can set the increment to be 0.1 mA in a particular embodiment so as to cover five different amplitudes over a period of five days, assuming the amplitude is incremented once every day. In other embodiments, the practitioner can select other suitable values, e.g., ranging from about 0.1 mA to about 2 mA, and ranging from about 0.5 days to about 5 days, with a representative value of from 1-2 days. 
     At process portion  307 , the starting amplitude is selected. The starting amplitude will typically be selected to be at a value that produces effective therapy. In process portion  309 , the therapy is applied to the patient at the starting frequency and starting amplitude. Process portion  311  includes receiving a response or efficacy measure from the patient. The response can include the patient providing a pain score in accordance with any of the scales or measures described above. The patient can provide this pain score via the patient remote  106  ( FIG. 1A ) so that the value is automatically stored, e.g., at the patient remote, or at the patient&#39;s implanted pulse generator. Process portion  313  includes determining the expected energy consumption associated with the combination of frequency and amplitude applied to the patient. This process can be executed by the patient remote  106  or other patient-controllable device, or by the implanted pulse generator (IPG)  101 , or by another device. In particular embodiments, the process of determining the expected energy consumption need not be conducted in the sequence shown in  FIG. 3 . Instead, it can be conducted after or before all the planned combinations of amplitude and frequency have been tested. In particular, a more accurate estimate of the energy consumption may include the actual time the patient uses each frequency and amplitude pair. In any of these embodiments, the energy consumption can be expressed in a variety of suitable manners, including energy per unit time (e.g., power). 
     Process portion  315  includes determining whether the efficacy, as indicated by the patient, has decreased by greater than a threshold amount relative to the baseline efficacy present at process portion  301 . The threshold amount can be selected by the patient and/or practitioner. For example, the threshold can be selected to be a 10%, 20%, 30%, 40% or other decrease from an initial or baseline efficacy value. If this is the first tested amplitude at the selected frequency, this step can be skipped. If not, and it is determined that the efficacy has not decreased by greater than a threshold amount, then the amplitude is incremented, as indicated at process portion  317 , and the steps of applying the therapy to the patient, receiving the patient&#39;s response and determining the expected energy consumption are repeated. If the efficacy has decreased by greater than the threshold amount, then the process moves to process portion  319 . Accordingly, the range within which the amplitude is increased is controlled by the threshold value. This range can also be governed or controlled by other limits. For example, the IPG can have manufacturer-set or practitioner-set limits on the amount by which the amplitude can be changed, and these limits can override amplitude values that might be within the efficacy thresholds described above. In addition, the patient can always override any active program by decreasing the amplitude or shutting the IPG down, via the patient remote  106  ( FIG. 1A ). 
     After it has been determined that the efficacy has decreased by at least the threshold amount, the amplitude is decreased at process portion  319 . In a particular embodiment, the amplitude can be decreased back to the starting amplitude set in process portion  307 , and the amplitude tests (with decreasing amplitude) can continue from that point. In another embodiment, if it is desired to re-test amplitudes that have already been tested in process portions  309 - 315 , those amplitudes can be re-tested as the amplitude is decremented from the value that resulted in the efficacy threshold being met or exceeded. 
     In process  321 , the therapy is applied to the patient at the decreased amplitude and the process of testing the therapeutic efficacy at multiple amplitudes is reiterated in a manner generally similar to that described above with reference to incrementing the amplitude. In particular, process portions  323  (receiving a response and/or efficacy measure from the patient), and process portion  325  (determining the expected energy consumption associated with the decreased amplitude) are repeated as the amplitude is decreased. In process portion  327 , the process includes determining whether the efficacy has decreased by greater than a threshold amount. This threshold amount can be the same as or different than the threshold amount used in process portion  315 . If it has not decreased by more than the threshold amount, the loop of decreasing amplitude (process portion  329 ), applying the signal to the patient, and testing the result is repeated until it does. 
     In process portion  331 , the process includes determining whether all frequencies to be tested have in fact been tested. If not, in process portion  333 , the frequency is changed and the process of incrementing and then decrementing the amplitude is repeated at the new frequency. If all frequencies have been tested, then process  335  includes selecting the signal or signals having or approximating a target combination of efficacy and energy consumption. 
     In a simple case, for example, if the practitioner tests 10 kHz and 1.5 kHz at a variety of amplitudes, process portion  335  can also be fairly simple. For example, process portion  335  can include determining if the lowest amplitude that produces effective therapy at 10 kHz also produces effective therapy at 1.5 kHz. If it does, then clearly the energy consumption at 1.5 kHz will be less than the energy consumption at 10 kHz, at the same amplitude. Accordingly, process portion  335  can include selecting the frequency to be 1.5 kHz for delivering additional signals to the patient. Furthermore, if it is clear that all tested amplitudes at 1.5 kHz will consume less energy than even the lowest amplitude at 10 kHz, then process portion  335  can include determining whether any of the amplitudes at 1.5 kHz produce effective pain relief. If any do, the process can include selecting the lowest amplitude that does so. 
     In other embodiments, process portion  335  can include a more involved process of pairing pain scores and energy consumption levels for each of the tested combinations and automatically or manually selecting the pair that produces the expected best efficacy at the expected lowest energy consumption. The energy consumption can be calculated, expressed, and/or otherwise described as a total amount of energy over a period of time, an energy rate (power) and/or other suitable values. The selection process will include weighting pain reduction and energy consumption in accordance with any preferences, e.g., patient-specific preferences. Accordingly, the patient may prefer a less-than-optimum pain score, but improved power consumption, or vice versa. In any of these embodiments, the selected signal is then applied to the patient in process portion  337 , e.g., to provide a course of therapy. The foregoing process can be repeated if desired, for example, if the patient&#39;s condition changes over the course of time. 
     One feature of the foregoing embodiments is that the manufacturer or practitioner can select the range of amplitudes over which the foregoing tests are conducted to be well higher than the point at which therapeutic efficacy is expected to decrease significantly, yet below the point at which the patient is expected to experience any uncomfortable or undesirable side effects. For example, in a particular embodiment, the patient is expected to receive effective therapeutic results at an amplitude range of from about 2 mA to about 6 mA. The overall amplitude test range can be selected to be between about 0 mA and about 10 mA or another suitable value that is not expected to produce undesirable side effects. As a result, the system can automatically test a suitable number of amplitude values and frequency values, without placing the patient in any discomfort. As a further result, the system can automatically test the foregoing amplitude and frequency values in an autonomous manner, without requiring practitioner or patient action, beyond the patient recording pain scores or other responses as the parameters change. Accordingly, the process for identifying an effective, low power consumption therapy signal can be more fully automated than existing processes and can accordingly be easier, less time-consuming, and/or less expensive to perform. 
     From the foregoing, it will be appreciated that specific embodiments of the presently-disclosed technology have been described herein for purposes of illustration, but that various modifications may be made without deviating from the disclosed technology. For example, several embodiments were described above in the context of variations in the amplitude and frequency of the signal, in order to determine an effective yet low-power therapy signal. In other embodiments, the process can include other parameters that are also varied to determine low-power effective therapy signals, in combination with amplitude and frequency, or in lieu of amplitude and frequency. Suitable signal parameters include pulse width, inter-pulse interval, and duty cycle. 
     Other embodiments of the present technology can include further variations. For example, instead of selecting an amplitude increment, as discussed above with reference to  FIG. 3 , a list of amplitude values can be used to increment and/or decrement from a starting amplitude value. The patient can receive a prompt (e.g., via the patient remote) when the system requires an input, such as a pain score. Instead of varying the amplitude at a constant frequency, the system can vary the frequency at a constant amplitude. Instead of first increasing amplitude and then decreasing amplitude, these processes can be reversed. In another embodiment the amplitude can be changed in only one direction, e.g., by starting at zero amplitude or starting at the top of the amplitude test range. 
     As discussed above, many of the steps for carrying out the foregoing processes are performed automatically, without continual involvement by the patient and/or practitioner. The instructions for carrying out these steps may be carried on any suitable computer-readable medium or media, and the medium or media may be distributed over one or more components. For example, certain steps may be carried out by instructions carried by the IPG, the patient remote and/or the physician&#39;s programmer, depending on the embodiment. Accordingly, a portion of the instructions may be carried by one device (e.g., instructions for receiving patient responses may be carried by the patient remote), and another portion of the instructions may be carried by another device (e.g., the instructions for incrementing and decrementing the amplitude may be carried by the IPG). 
     Certain aspects of the technology described in the context of particular embodiments may be combined or eliminated in other embodiments. For example, in some embodiments, the foregoing process can include only incrementing the amplitude or only decrementing the amplitude, rather than both, as discussed above. In other embodiments, certain steps of the overall process can be re-ordered. For example, the expected energy consumption value can be determined before or after receiving a response from the patient, and/or can be performed on a list of amplitude values all at one time. In some embodiments, certain amplitude/response pairs may be eliminated from consideration or from further calculations, e.g., if the data are determined to be defective, and/or for any other suitable reason. 
     3.0 Additional Embodiments 
     In one embodiment, there is provided a method for programming a spinal cord stimulation system for providing pain relief to a patient. The method comprises configuring a signal generator to deliver a first therapy signal at a first frequency, and a second therapy signal at a second frequency different than the first. For both the first and second signals, the method includes carrying out the following processes: (i) increasing an amplitude of the signal, over multiple steps, from a baseline amplitude at which the patient has a baseline response; (ii) for individual step increases, determining the patient&#39;s response to the increased amplitude; (iii) decreasing the amplitude over multiple steps; and (iv) for individual step decreases, determining the patient&#39;s response to the decreased amplitude. The method can further include comparing the patient responses to the first therapy signal with the patient responses to the second therapy signal and, based on the patient responses and an expected energy consumption for the first and second therapy signals, selecting one of the first and second therapy signals for additional therapy to the patient. 
     In particular embodiments, the first frequency can be in a frequency range from 10 kHz to 100 kHz, inclusive, and the second frequency can be in a frequency range from 1.5 kHz to 10 kHz. The process of increasing or decreasing the amplitude can be halted if the pain score worsens by a threshold value, and the threshold value can vary from 10% to 40%, in particular embodiments. 
     Another representative embodiment of the technology is directed to a spinal cord stimulation system. The system comprises a signal generator coupleable to a signal delivery device to deliver electrical therapy signals to a patient at a first frequency and a second frequency different than the first. The system can further include a computer-readable medium programmed with instructions that, when executed, for both the first and second signals: (i) increases an amplitude of the signal, over multiple steps, from a baseline amplitude at which the patient has a baseline response; (ii) at individual step increases, receives the pain score based on the patient&#39;s response to the increased amplitude; (iii) decreases the amplitude over multiple steps; and (iv) for individual step decreases, receives the pain score based on the patient&#39;s response to the decreased amplitude. The instructions compare the pain scores corresponding to the first therapy signal with the pain scores corresponding to the second therapy signal. Based on the pain scores and an expected energy consumption for each of the first and second therapy signals, the instructions determine one of the first and second therapy signals for additional therapy to the patient.