Abstract:
A patient activity level recorder and a patient therapy adjustment recorder are provided to obtain an historical representation of patient activity levels and therapy changes in the form of profiles which are stored for later retrieval. The patient activity level profile and the therapy adjustment profile may be used to objectively interpreting subjective patient information. The activity level recorder may include an accelerometer, the output of which is processed by a signal processor, programmed to interpret the sensor raw signal as one of a plurality of predetermined activity levels. In a preferred embodiment, data for rest, moderate and vigorous activity levels for each day in a recording period are stored for later retrieval and use by a physician, or possible by the patient where therapy is self-administered. The therapy adjustment recorder may include a processor for interpreting signals from a patient control interface to a pulse generator of a spinal chord stimulation system.

Description:
This is a continuation of application Ser. No. 09/070,348, filed Apr. 30, 1998, U.S. Pat. No. 6,120,467, for which priority is claimed. This parent application is incorporated herein by reference in its entirety. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to systems for obtaining objective patient data, for example, by monitoring patient physiologic and metabolic activity and adjustments to patient therapy. More particularly, the invention relates to a system and method for obtaining objective information about patient activity levels, activity patterns and patient-activated changes in Spinal Cord Stimulation (SCS) therapy and using such objective information to interpret subjective patient responses to physician inquiry. 
     BACKGROUND OF THE INVENTION 
     SCS therapy is a relatively recent development in which electrical stimulation is applied to the central nervous system in the spinal cord area for the relief of pain of the trunk and/or limbs. Presently, there exist no known techniques for objectively determining the efficacy of an SCS system. Typically, efficacy determinations for SCS systems rely on empirical methods which are based on information conveyed from the patient to clinicians. For example, to assess efficacy a physician will interview a patient and ask simple questions relative, for example, to the level of pain that the patient is or has been experiencing after SCS has been implemented. 
     Currently, the practice of adjusting or optimizing post-implantation parameters in SCS systems relies exclusively on patient-reported feedback. Patient reporting is subject to the patient&#39;s own perception of symptoms. This prevents objective determinations of symptomatic conditions and leaves diagnostic procedures prone to inappropriate assumptions about the existing or potential efficacy of SCS in a given patient. To illustrate the problem, one can imagine a patient being treated with SCS who experiences significant pain reduction. As a result of the reduction in pain, the patient becomes more active, and takes part in day-to-day activities that were not undertaken before SCS treatment. That increase in activity actually causes the patient to experience more pain which may not necessarily be due to the condition treated with SCS, but instead may be the result of the heightened activity level. When asked whether pain has decreased, the patient may very well respond that it has not, even though the SCS may actually be mitigating the pain level. Thus, present efficacy evaluation techniques do not allow for a objective qualification of patient reported data. 
     It would therefore be desirable to provide a system which enables objective interpretation of subjective information regarding the efficacy of an SCS system. In particular, it would be desirable to provide a system which permits storage and retrieval of an historical representation of objective patient data, including patient activity levels and therapy adjustments to provide a physician with an objective reference to subjective patient information. 
     SUMMARY OF THE INVENTION 
     The invention achieves the aforementioned objectives by providing, according to a preferred embodiment, a system for monitoring and obtaining an historical representation or profile of the activity level and/or therapy adjustments of a patient. An activity level recorder, which is preferably incorporated into the structure of an SCS implantable generator, senses, according to output from an accelerometer and possibly other sensors, the amount of activity a patient is experiencing. The activity recorder is provided with a processor which is programmed to translate and categorize sensor output data into a number of predetermined activity categories. A patient activity level profile includes data about the activity undertaken by the patient in each of the different activity categories and is stored for later retrieval. A physician may then retrieve and review the activity level profile use it to objectively interpret subjective information obtained by interviewing the patient. 
     According to a preferred embodiment, activity levels for rest, moderate and vigorous activity are stored in daily profiles, which provide values for the amount of time that a patient has experienced each respective activity level. A physician viewing the daily profiles may determine whether a particular day included a significant amount of vigorous activity, for example, or whether a particular day was generally sedentary. Thus, an advantage provided by the present invention is that information obtained by interview regarding pain experience for a particular day may be objectively interpreted with regard to the activity level for that day or preceding days. 
     According to another feature of the invention, a therapy adjustment recorder is provided for storing one or more profiles representing the type and time of various patient therapy adjustments. Such adjustments may include adjustments to the pulse width, frequency and amplitude of an SCS signal. The patient therapy adjustment profiles may be stored in the therapy adjustment recorder for later retrieval by a physician. Therapy adjustment profiles provide another objective standard by which physicians may evaluate subjective patient data. 
     Other objects, advantages novel features, and the further scope of applicability of the present invention will be set forth in the detailed description to follow, taken in conjunction with the accompanying drawings, and in part will become apparent to those skilled in the art upon examination of the following, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The accompanying drawings which are incorporated into and form a part of the specification, illustrate several embodiments of the present invention and, together with the description, serve to explain the principles of the invention. The drawings are only for the purpose of illustrating a preferred embodiment of the invention and are not to be construed as limiting the invention. In the drawings, in which like numbers refer to like parts throughout: 
     FIG. 1 is a block diagram of a device for obtaining a historical representation of patient activity levels according to a preferred embodiment of the invention; 
     FIG. 2 is a flow diagram illustrating the steps of a process for generating patient activity level profiles according to a preferred embodiment of the invention; 
     FIGS. 3A and 3B are illustrations of activity level profiles according to a preferred embodiment of the invention; 
     FIG. 4 is a schematic illustration of a therapy adjustment recorder for obtaining a therapy adjustment profile according to a preferred embodiment of the present invention; and 
     FIG. 5 is a flow diagram illustrating the steps of a process for adjusting patient therapy according to a preferred embodiment of the invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 depicts in block diagram form an activity level recorder  10  for obtaining an historical representation of patient activity levels according to a preferred embodiment of the present invention. In the presently preferred embodiment of the invention, a sensor  12  is provided for generating a signal corresponding to activity undertaken by the patient. Sensor  12  may utilize a piezoelectric accelerometer for measuring changes in movement of the patient, patient&#39;s limbs or both. Preferably, sensor  12  is installed as an accelerometer mounted on the electronic circuit board inside of an implantable SCS generator. 
     Sensor  12  provides a raw electrical signal to a signal processor  18 , which may include an analog-to-digital (A/D) converter  14  for converting the analog raw signal from sensor  12  into digital form, a filter  16 , which may be a bandpass filter, for screening background noise from the sensor output signal, and a central processing unit (CPU)  17  for executing a sequence of processing instructions stored in RAM  22  and/or ROM  24  in a manner described below. It will be recognized that A/D converter  14  and filter  16  may be interchanged to obtain desired signal processing characteristics. CPU  17  is provided with an internal clock and calendar maintaining temporal orientation with respect to the processing of the sensor output signal. A power supply  26  is provided, preferably in the form of a battery, for supplying electrical energy to CPU and other system components which require it. 
     Those of ordinary skill will recognize that the invention contemplates alternative devices for sensing patient activity. For example, sensors which give a reading of certain metabolic activity could be substituted for or used in conjunction with the accelerometer. Conventional devices for sensing heart rate, respiration and body temperature, for example, could be employed to replace or augment the data output of sensor  12 . 
     FIG. 2 illustrates a flow diagram depicting the process steps accomplished by signal processor  18 . It will be recognized by those of ordinary skill in the art that FIG. 2 represents an iterative process which may be executed many times per second or may be executed, for example, once every 10 seconds. At state  30 , the current value of the sensor output signal is obtained by the signal processor  18 . At state  32 , a long-term average value for patient activity level, LTACTLEV is obtained. The value for LTACTLEV is computed by time-averaging the sensor output signal level over a time period corresponding preferably from one to four hours. As will be recognized, the process depicted in FIG. 2 would have to be initially executed for such a duration in order to determine the value of LTACTLEV. For each iteration, a running value of LTACTLEV may be determined by adding the value corresponding to the sensor output signal to a running sum of previous values over the four-hour interval and dividing that sum by the total number of processor clocking intervals corresponding to four hours. 
     At state  34 , a short-term value for patient activity level STACTLEV is determined. STACTLEV is computed by time-averaging the sensor output signal level over a time period corresponding preferably to between 2 and 60 seconds. At state  37 , a comparison is made to. determine the relative values of STACTLEV and LTACTLEV. If it is determined that STACTLEV is much greater than LTACTLEV, for example, if STACTLEV exceeds LTACTLEV by a factor of 3, the signal processor branches to step  38 . At step  38 , a vigorous activity register, which may be defined as a location in RAM  22 , is incremented with a time value corresponding to the clocking cycle of the depicted process. For example, if the process is programmed to occur at one-second intervals, then the vigorous activity register would be incremented by a value of one. 
     If the condition defined in step  37  is not met, the process continues to step  40  to determine if the sensor output signal corresponds to moderate activity level. At step  40 , a determination is made as to whether STACTLEV exceeds LTACTLEV by, for example a factor of 2. If so, the process branches to state  42  where a moderate activity register is incremented. If the condition defined in step  40  is not met, the process continues to step  44  where, logically, the sensor output level must correspond to a resting condition and a rest activity register is incremented. 
     As shown in FIG. 2, each of states  38 ,  42  and  44  branch to a decision block  46  where a determination is made as to whether a 24-hour daily period has expired. Such a determination may be implemented, for example, by a running counter the value of which is checked at state  46  to determine if it corresponds to a 24-hour period. If it is determined that the daily clock has not expired, the process returns to state  30  for another iteration. However, if it is determined at state  46  that the 24 hour clock as expired, then the process branches to state  48  where daily values are stored in appropriate locations in RAM  22 . The daily values for the vigorous and moderate activity levels and the rest activity level will correspond to the values stored in the respective registers. Thus, state  48  may be implemented by simply reading the value of the activity registers and writing that value to an assigned memory location corresponding to a particular day. 
     The process proceeds to state  50  where the day counter is incremented to signify the start of a new 24-hour period. Appropriately, the three activity level registers described above are reset to zero values at state  52  and the process returns to state  30  to begin monitoring activity levels for the next day. 
     FIG. 3A illustrates a patient activity level profile that may be stored in RAM  22  and later retrieved in a manner to be described below. The data may be stored in the form of a matrix which is visualized in the form of a table  50  that contains corresponding activity levels for each day of monitoring. For example, DAY  1  is assigned corresponding values for rest, moderate and vigorous activity levels of 14, 8 and 2 hours. DAY  2  corresponds to respective values of 20.3, 3.7 and zero. Referring again to FIG. 1, a reporting interface  26  is provided to CPU  17  to enable retrieval of the patient activity level profile stored in RAM  22 . Reporting interface  26  may be provided in the form of an input/output bus or serial port, the details of which are well known to those of ordinary skill in the art. It will be recognized by those of ordinary skill that the number of activity categories may be varied such that, for example, five activity categories instead of three are provided. Similarly, while daily reporting intervals are described with respect to FIG. 3A, the duration and number of reporting intervals may be varied. 
     FIG. 3B illustrates another form of an historical representation of patient activity level data that may be stored in RAM  22 . Here, a curve is represented for a 60-day interval for one of the activity level categories, in this case, moderate activity, as a percentage of daily activity. Such an activity level profile provides a physician with a readily-apparent indication of activity trends. 
     FIG. 4 illustrates a block diagram of a therapy adjustment recorder according to a preferred embodiment of the invention. Several commercially available SCS systems have functions that allow the patient to alter the parameters characterizing the therapy delivered to the patient. For example, the ITREL 3  system manufactured by Medtronic, Inc. of Minneapolis, Minn., permits patient altering of the pulse frequency, pulse amplitude and pulse width in an SCS system. Settings are altered via hand-held radio frequency which communicates via telemetry with an implanted SCS pulse generator. Such a system is schematically represented in FIG. 4 along with the therapy adjustment profile generator according to a preferred embodiment of the present invention. SCS generator  62  is in electrical communication with an implanted lead (not shown) for delivering electrical stimulation to excitable tissue in the spinal dura. Through a radio frequency link  66 , SCS generator  62  communicates with a patient control interface  64  for permitting a patient to adjust various parameters of the electrical stimulation applied to the excitable tissue. In accordance with the present invention, a therapy adjustment profile generator  80  comprises a data bus  82  which conveys data indicating the various parameters to a processor  68  which includes an internal clock  69  and timekeeping functions. Time and parameter data are periodically stored in storage  70  which is a memory device. Thus, particular parameter settings and changes therein may be correlated with particular times and days to form a therapy adjustment profile stored in storage  70 . Processor  68  operates according to pre-programmed instructions to permit on-demand exporting of the therapy adjustment profile and retrieval by a physician. Once the information is stored in storage  70 , the patient control interface  64  can send that information via RF to a physician control interface  90 . This instrument can then display or print the information in several different formats. Reporting interface  72  provides an interface to processor  68  for enabling retrieval of a stored patient activity level profile. 
     FIG. 5 illustrates the process steps according to a preferred embodiment of the invention by which a physician may adjust patient therapy based on the objective data provided by the patient activity level recorder and the patient therapy adjustment recorder described above. In this example, it will be assumed for simplicity that only two therapy settings where undertaken by the patient, settings “A” and “B”. At. steps  100  and  101 , respectively, the physician retrieves the therapy adjustment profile and activity level profile through respective reporting interfaces. At step  102 , the patient is interviewed to determine whether setting “A” offered more beneficial therapy. In the event that the patient characterizes setting “A” as better, the method proceeds to state  104  where the activity level profile is reviewed to determine if ACTLEVEL(A)—the general activity level corresponding to therapy setting “A”—was much less than ACTLEVEL(B)—the general activity level corresponding to therapy setting “B”. If not, the physician selects therapy setting “A” as represented at state  106 . If, on the other hand, ACTLEVEL(A) is much less than that ACTLEVEL(B), the method proceeds to state  108 . This step would indicate that the patient undertook generally much less activity under setting “A”. Thus, at state  108 , the physician considers whether therapy setting “B” is more beneficial to the patient, despite the patient&#39;s indicated preference for therapy setting “A”. Further inquiry may be undertaken to reconcile the increased activity level corresponding to setting “B”. Thus, the patient activity level data and patient therapy adjustment level data are utilized to objectively qualify the patient&#39;s subjective preference for setting “A”. 
     Still referring to FIG. 5, in the event that the patient, at state  102 , does not indicate that therapy setting “A” is preferred, the method continues to state  110  where further inquiry is made as to the patient&#39;s preference for therapy setting “B”. If such a preference is indicated, the method branches to state  112  where the activity level profile is analyzed to determine whether ACTLEVEL(A) greatly exceeds ACTLEVEL(B). If that condition is met, the physician proceeds to step  116  where consideration of therapy setting “A” is made and further inquiry is conducted to reconcile the increased activity level corresponding to activity level “A”. If the condition at state  112  is not met, the physician selects therapy setting “B” at state  114 . 
     As denoted by state  118 , if neither condition at state  102  or state  110  is met, the method requires analysis of the activity level profile to determine whether ACTLEVEL(A) is greater than ACTLEVEL(B). Such a condition would indicate that the patient undertook more activity under therapy setting “A” than under therapy setting “B”. In that case, therapy “A” is selected at state  120 . If the condition at state  118  is not met, the activity level profile is analyzed to determine whether ACTLEVEL(B) is greater than ACTLEVEL(A) at state  122 . If that condition is met, therapy setting “B” is selected at state  124 . If no difference between the activity levels corresponding to respective therapy settings “A” and “B” is noticeable, then either therapy setting may be selected as denoted at state  126 . 
     Those skilled in the art will recognize that the preferred embodiments may be altered or amended without departing from the true spirit and scope of the invention, as defined in the accompanying claims.