Patent Publication Number: US-7218968-B2

Title: User interface for programming rate response technical field

Description:
TECHNICAL FIELD 
   The invention relates to rate responsive therapy in general and, more particularly, to techniques for programming the rate responsive behavior of an implantable medical device. 
   BACKGROUND 
   Implantable medical devices that are rate responsive monitor one or more physiological parameters of patients in which they are implanted, and adjust the rate of one or more stimulation outputs based on changes in these physiological parameters. For example, a rate responsive pacemaker may monitor one or more physiological parameters that indicate an activity level of a patient, such as patient motion, respiration, temperature, blood pressure, blood pH, blood oxygen and/or the lengths of various intervals within an electrocardiogram of the patient. A rate responsive pacemaker adjusts the rate at which pacing pulses are delivered to the heart of the patient in the absence of a sensed depolarization, by adjusting one or more escape intervals based on the changes in these physiological parameters. In general, a rate responsive pacemaker attempts to ensure that the heart rate of a patient is appropriate for the current activity level of the patient. 
   The rate response behavior of a rate responsive pacemaker is controlled by a number of programmed parameters stored within the pacemaker. A physician, clinician, or the like, may use a programmer that communicates with the pacemaker to program or reprogram these parameters. For example, a physician or clinician may specify ranges of heart rates and the rate response, i.e., the relationship between the output of the one or more sensors and the rate at which pacing pulses are delivered to a patient in the absence of a sensed depolarization, within those ranges. The programmer may direct the pacemaker to change the values of the parameters stored therein in response to the input provided by the physician or clinician. For some physicians and clinicians, the use of existing programmers and associated techniques to program these parameters has proven to be unintuitive, and, in some cases, confusing. 
   Often, in order to arrive at an appropriate rate response for a particular patient, a physician or clinician first programs the pacemaker, and then subjects the patient to an exercise test in order to determine the effectiveness of the current parameters at a variety of activity levels. The pacemaker may store data that indicates its rate response performance during the exercise test, and the programmer may retrieve this information and display it to the physician in some form such that the physician may evaluate it. In some cases, this process must be repeated multiple times before an appropriate rate response for that particular patient is achieved. Further, as the condition of the patient and/or the pacemaker changes, it may be determined on a follow-up visit to the clinic that the previously programmed parameters are no longer effective, requiring that the physician or clinician again subject the patient to this programming process. 
   Pacemakers that automatically optimize rate response parameters may allow physicians and patients to avoid multiple programming and exercise test iterations. In general, pacemakers that optimize rate response receive one or more performance targets from the physician, such as a target percentage of time for the sensor indicated rate to be within a particular range of rates, determine whether the performance targets are being met, and, if necessary, adjust the parameters to meet the targets. However, it may take two or more weeks for a pacemaker to reach the optimized rate response, and for the patient to feel better. Moreover, after this delay, the optimized rate response may still not be adequate if the physician erred in choosing the performance targets. 
   SUMMARY 
   In general, the invention is directed to a programmer including a user interface, and techniques for programming a rate responsive implantable medical device using such a programmer and user interface. The programmer may interrogate an implantable medical device to retrieve programmed rate response parameters and optimization target values of the implantable medical device. The programmer may display the currently programmed rate response parameters and optimization target values via a user interface. The programmer may also generate a current rate response curve and a current target rate histogram, and display the current rate response curve and current target rate histogram via the user interface. 
   The programmer may receive changes to the displayed currently programmed rate response parameters and/or target values made by a user via the user interface, generate a pending rate response curve and/or a pending target rate histogram based on these changes, i.e., pending parameters or target values, and display the pending rate response curve and/or pending target rate histogram via the user interface. A user may accept the pending parameters and/or optimization target values via the user interface, and the programmer may reprogram the implantable medical device with the pending parameters or optimization target values based on the acceptance. 
   In one embodiment, the invention is directed to a method that includes receiving currently programmed rate response parameters and at least one currently programmed optimization target value from an implantable medical device, and displaying the currently programmed parameters and at least one target value via a user interface. The method further includes generating a current rate response curve based on the parameters and a current target rate histogram based on the parameters and at least one target value, and displaying the curve and the histogram via the user interface. 
   In another embodiment, the invention is directed to a computer-readable medium containing instructions. The instructions cause a programmable processor to receive currently programmed rate response parameters and at least one currently programmed optimization target value from an implantable medical device, and display the currently programmed parameters and at least one target value via a user interface. The medium also includes instructions that cause a processor to generate a current rate response curve based on the parameters and a current target rate histogram based on the parameters and at least one target value, and display the curve and the histogram via the user interface. 
   In another embodiment, the invention is directed to a device that includes a transceiver to communicate with an implantable medical device and a processor. The processor receives currently programmed rate response parameters and at least one currently programmed optimization target value from the implantable medical device via the transceiver, and displays the currently programmed parameters and at least one target value via a user interface. The processor also generates a current rate response curve based on the parameters and a current target rate histogram based on the parameters and at least one target value, and displays the curve and the histogram via the user interface. 
   In another embodiment, the invention is directed to a method that includes receiving at least one rate response optimization target value, generating a target rate histogram based on the at least one received target value, and displaying the target rate histogram via a user interface. 
   In another embodiment, the invention is directed to a computer-readable medium containing instructions. The instructions cause a programmable processor to receive at least one rate response optimization target value, generate a target rate histogram based on the at least one received target value, and display the target rate histogram via a user interface. 
   The invention is capable of providing one or more advantages. For example, a programmer that displays a current rate response curve or current target rate histogram via a user interface may allow the user to more easily visualize the current programming of an implantable medical device, and the effect of the current programming on a patient in whom the medical device is implanted. Further, a programmer that displays a pending rate response curve or pending target rate histogram via a user interface based on pending changes to the programming made by a user via the user interface may allow the user to more easily visualize the effect that those pending changes would have on the rate response of an implantable medical device and a patient in whom the medical device is implanted, if they were accepted and used to reprogram the implantable medical device. In some embodiments, the programmer displays current and pending curves or histograms side-by-side, further increasing the ability of a user to understand the effect of pending changes to the programming of the implantable medical device. A user of such a programmer may evaluate the effect of these changes before submitting them to the implantable medical device, i.e. without reprogramming the implantable medical device with the changes, and without an exercise test. 
   Some programmer embodiments may provide a user interface with slider-bar fields, arrows, or buttons indicating “more” and “less” aggressive rate response. Such embodiments provide an intuitive interface for a user to adjust the aggressiveness of the rate response of an implantable medical device. Using such interfaces, a user need not understand the relationship between various parameters that control the rate response of the implantable device in order to effectively adjust the rate response of the implantable medical device. 
   Some programmer embodiments capable of rate response optimization may associate changes in optimization target values with changes in other programmed parameters that control the rate response of the implantable medical device. When the user intends to change an optimization target value, the corresponding change in the programmed parameters will advantageously bring them closer to the values that the implantable medical device would arrive at through optimization based on the changed optimization target values. Thus, at the time of programming, the rate response of the implantable medical device will be closer to the eventual optimized response, allowing the patient to more quickly feel the effect of the changes, and the user to more quickly evaluate whether the changes made are effective. 
   The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims. 

   
     BRIEF DESCRIPTION OF DRAWINGS 
       FIG. 1  is a perspective diagram illustrating a programmer to program the rate response behavior of an implantable medical device. 
       FIG. 2  is a block diagram illustrating the programmer of  FIG. 1  in greater detail. 
       FIGS. 3A–3F  are diagrams illustrating an exemplary user interface that may be provided by the programmer of  FIGS. 1 and 2 . 
       FIG. 4  is a flow diagram illustrating an exemplary method for programming a rate responsive implantable medical device via a programmer that includes user interface. 
       FIG. 5  is a flow diagram illustrating an exemplary method for generating current and pending rate response curves. 
       FIG. 6  is a flow diagram illustrating an exemplary method for generating a current or pending target rate histogram. 
       FIG. 7  is a flow diagram illustrating an exemplary method for adjusting rate response curve values and optimization target values based on user interaction with rate response curve value fields. 
   

   DETAILED DESCRIPTION 
     FIG. 1  is a perspective diagram illustrating a programmer  10  to program the rate response of an implantable medical device (IMD)  12  implanted within a patient  14 . As illustrated in  FIG. 1 , IMD  12  may be a rate responsive pacemaker or rate responsive implantable cardioverter-defibrillator. Embodiments of programmer  10  that interact with a rate-responsive pacemaker embodiment of IMD  12  will be described herein. 
   However, the invention is not so limited, and may be applied to any programmer  10  for programming any rate-responsive medical device. 
   A user (not shown) of programmer  10 , such as a clinician or physician, interacts with programmer  10  and IMD  12  via a user interface. A user may interact with the user interface provided by programmer  10  via a keyboard  18  and a monitor  20 , which may for example, be a CRT monitor, LCD monitor, LED monitor, or the like. Programmer  10  may also include a pointing device, such as a mouse, via which a user may interact with the user interface. Programmer  10  is in wireless communication with IMD  12 . Programmer  10  may, for example, communicate with IMD  12  by wireless transmission via a programming head (not shown) placed over IMD  12  and telemetry circuits of IMD  12  as is known in the art. 
   IMD  12  may include a memory to store data reflecting electrical activity sensed in heart  16 , the output of various other sensors of IMD  12 , such as one or more sensors used to control the rate response of IMD  12 , and the rate response of IMD  12  over time. The rate response of IMD  12  is controlled by a number of programmed parameters stored by IMD  12 . IMD  12  may also provide for the optimization of some of these parameters based on one or more optimization target values provided by a user and stored by IMD  12 . Programmer  10  may interrogate IMD  12  to retrieve the data, and the currently programmed parameters and optimization target values stored by IMD  12 , and display some or all of these items to a user via the user interface provided by programmer  10 . A user may also program or reprogram the rate response of IMD  12  via the user interface by, for example, providing or adjusting rate response parameters or target values. The user interface provided by programmer  10  may provide a number of advantages which may simplify the programming or reprogramming of IMD  12  by a user, as will be discussed in greater detail below. 
   IMD  12  may deliver pacing pulses to heart  16  of patient  14  on demand, or as otherwise programmed, as controlled by a rate control signal which is determined based on the output of the one or more physiological sensors (not shown). IMD  12  may include one or more physiological sensors that generate output signals that vary based on the activity level of patient  14 . For example, IMD  12  may include a sensor that detects the motion of the patient, e.g., an activity sensor or accelerometer, which may be a piezoelectric crystal, a sensor that monitors respiration, e.g., a sensor that measures thoracic impedance, a sensor that monitors patient temperature, a sensor that monitors blood pressure at some location within the circulatory system of the patient, a sensor that monitors the pH of blood of the patient, a sensor that monitors the level of oxygen within the blood of the patient, or IMD  12  may monitor lengths of various intervals within an electrocardiogram of the patient. In an exemplary embodiment, IMD  12  is a dual sensor rate responsive pacemaker that includes a sensor to detect motion of patient  14  and a sensor that monitors the respiration of patient  14 . In such an embodiment, IMD  12  may determine the weights or relative contributions of the signals generated by each sensor to the rate control signal used to determine the sensor indicated heart rate, i.e., the rate that IMD  12  will pace heart  16  at in the absence of a sensed ventricular depolarization. 
   As mentioned above, IMD  12  determines sensor indicated rate, i.e., the rate response of IMD  12  based on a number of programmed parameters. These programmed parameters may be received from a user via the user interface of programmer  10 , and stored in a memory of IMD  12 . These programmed parameters may include rate limits, such as a lower rate (LR) and an upper sensor rate (USR). The LR and USR are the minimum and maximum sensor indicated rates available to IMD  12 , i.e., the minimum and maximum rates at which IMD  12  will pace heart  16 , respectively. 
   These programmed parameters may also include one or more setpoint values that indicate a currently programmed or selected curve used to determine the sensor indicated rate based on the output of the sensors. IMD  12  may store a family of curves or look-up tables that relate sensor output to sensor indicated rate. These curves provide varying levels of rate response at a given output of the sensors, i.e., have varying slopes from the LR to the USR. The greater the slope of a curve is, the more aggressive the rate response of IMD  12  employing that curve across a range of sensor outputs will be. IMD  12  determines a sensor indicated rate for a sensor output by comparing the sensor output to the currently programmed or selected curve. Through the selection of curves or tables, a user may provide a customized rate response for patient  14  that is appropriate for the condition and overall activity level of patient  14  via IMD  12 . 
   In some embodiments, IMD  12  may be a dual-slope rate responsive pacemaker. Programmed parameters for a dual-slope embodiment of IMD  12  also include a third rate limit that falls between the LR and USR. This third rate limit may divide the effective rate range of such an embodiment of IMD  12  into two rate ranges, from the LR to the third rate, and from the third rate to the USR. 
   IMD  12  may provide a first rate response within the range from the LR to the third rate, and a second rate response within the range form the third rate to the USR. In other words, IMD  12  may maintain a separate family of curves with associated setpoint values for each of these ranges, and a user may select the curve within each range by programming a setpoint for each range. Through the selection of curves or tables in a dual-slope device, a user may provide a customized rate response for patient  14  via IMD  12  that is not only appropriate for the condition and overall activity level of patient  14 , but is appropriate within the distinct ranges of activity levels and heart rates. 
   A user may select a curve for the range between the LR and the third rate that provides a desired rate response during normal daily activities of patient  14 , such as getting into and out of bed, walking around the house, and the like. Thus, the third rate may be referred to as the activities of daily living rate (ADLR). The range of rates between the LR and the ADLR may be referred to as the ADL range. The user may select a curve for the range between the ADLR and USR that provides a desired rate response during more strenuous activities, such as exercising. The range between the ADLR and USR may be referred to as the exertion range. 
   The rate response of IMD  12  may also be controlled by parameters that control how quickly IMD  12  reaches a sensor indicated rate. An attack constant may control how quickly IMD  12  can increase the sensor indicated rate in response to increased output of the sensors. A decay constant may control how slowly IMD  12  can decrease the sensor indicated rate in response to decreased output of the sensors. 
   As mentioned above, IMD  12  may optimize some of these programmed parameters, and thus the rate response of IMD  12 , based on one or more optimization target values received from a user and stored in a memory of IMD  12 . In general, IMD  12  optimizes the rate response parameters by adjusting setpoint values, i.e., selecting different curves, in order to meet the optimization target value. In some embodiments of IMD  12 , an optimization target value may be a percentage of time that IMD  12 , through changes made to programmed parameters via the optimization program, will cause the sensor indicated rate to be within a rate range. Some dual-slope embodiments of IMD  12  may receive two optimization target values from a user. The first optimization target value may be a percentage of time that IMD  12  will cause the sensor indicated rate to be within the range from the ADLR to the USR, and may be referred to as the ADL percentage. The second optimization target value may be a percentage of time the IMD  12  will cause the sensor indicated rate to be at the USR, and may be referred to as the USR percentage. 
   As will be described in greater detail below, programmer  10 , via the user interface, provides a user with a depiction of the current rate response of IMD  12  in the form of a curve that relates activity level to sensor indicated rate based on currently programmed parameters received from IMD  12 , and may provide a depiction of a current target distribution of the sensor indicated rate over time that is to be or has been caused by currently programmed optimization target values. Programmer  10  may also provide a pending rate response curve, and a pending target distribution of the sensor indicated rate via the user interface based on changes to parameters and/or target values made by a user via the user interface. The heart rate distributions may be displayed as rate histograms that show estimated percentages of time IMD  12  will cause the heart rate to be in discrete rate ranges, or bins, based on the currently programmed parameters and optimization target values. 
   Display of the current rate response curve and current target rate histogram by programmer  10  via the user interface may allow the user to more easily visualize the current programming of IMD  12 , and its effect on patient  14 . Display of pending rate response curve and target rate histograms by programmer  10  may allow the user to more easily visualize the effect of the changes made on the rate response of IMD  12  and patient  14 , making programming IMD  12  more intuitive for the user. Moreover, the user may evaluate the effect of these changes before submitting them to IMD  12 , i.e. without reprogramming IMD  12  with the changed parameters or target values, and without an exercise test. 
     FIG. 2  is a block diagram illustrating programmer  10  in greater detail. As shown in  FIG. 2 , programmer  10  includes a processor  30 , a transceiver  32 , and an antenna  34 . As mentioned above, programmer  10  may be in wireless communication with IMD  12 . Processor  30  may receive data collected by IMD  12 , currently programmed rate response parameters, and currently programmed optimization target values from IMD  12 , and may reprogram IMD  12  by providing new parameters and/or optimization target values to IMD  12  via transceiver  32  and antenna  34 . Antenna  34  may correspond to the programming head that may be placed over heart  16  as described above with reference to  FIG. 1 . 
   As discussed above, programmer  10  provides a user interface  36  by which a user of programmer  10 , such as a clinician or physician, interacts with programmer  10  and IMD  12 . User interface  36  may be a graphical user interface displayed on monitor  20 , and a user may interact with user interface  36  via monitor  20 , keyboard  18 , and/or a pointing device, illustrated in  FIG. 1 . Processor  30  may provide user interface  36  as described herein. A memory  38  may store program code that causes processor  30  to provide user interface  36  as described herein, and the functionality ascribed to user interface  36  herein. Memory  38  may include any fixed or removable magnetic or optical media, such as RAM, ROM, CD-ROM, hard or floppy magnetic disks, EEPROM, or the like. 
   As will be described in greater detail below, processor  30  may display data collected by IMD  12 , currently programmed rate response parameters and optimization target values retrieved from IMD  12  via user interface  36 . Processor  30  may also generate a current rate response curve and a current target rate histogram, and display the current rate response curve and current target rate histogram via user interface  36 . Processor  36  may receive changes to the currently programmed rate response parameters and/or target values made by a user via user interface  36 , generate a pending rate response curve and/or a pending target rate histogram based on these changes, and display the pending rate response curve and/or pending target rate histogram via user interface  36 . A user may accept the changes made to the programmed parameters and/or optimization target values via user interface  36 , and programmer  10  may direct IMD  12  to change the parameters or optimization target values stored within a memory of IMD  12  based on the acceptance. 
     FIGS. 3A–3F  are diagrams illustrating an exemplary embodiment of user interface  36  that may be provided by processor  30 . The embodiment of user interface  36  illustrated in  FIGS. 3A–3F  is an embodiment that may be provided by processor  30  to allow a user to program or reprogram a dual-slope rate responsive pacemaker embodiment of IMD  12 . It is to be understood, however, that the invention is not limited to embodiments of user interface  36  for programming or reprogramming dual-slope rate responsive pacemakers. Nor is the invention limited to embodiments of user interface  36  that display the information that user interface  36  is depicted as displaying in  FIGS. 3A–3F , that display the information in the same manner as user interface  36  is depicted as displaying in  FIGS. 3A–3F , or that provide buttons, drop-down menus, text boxes, slider-bars, or the like in the same manner as user interface  36  is depicted as providing in  FIGS. 3A–3F . Moreover, embodiments of user interface  36  consistent with the invention may provide additional screens, windows, fields, functionality, and the like, not illustrated in  FIGS. 3A–3F . 
     FIG. 3A  illustrates user interface  36  after processor  30  has retrieved data, currently programmed rate response parameters and, in some cases, currently programmed optimization target values stored within a memory of IMD  12 . As mentioned above, processor  30  may display some of the currently programmed parameters via user interface  36 . For example, as shown in  FIG. 3A , processor  30  may display the programmed rate limits, e.g., the LR, ADLR, and USR, within fields  40 – 44 . Fields  40 – 44  may comprise drop-down menus, text boxes, or drop-down menus with text boxes, and a user may make changes to the programmed rate limits displayed in fields  40 – 44  by clicking on and/or typing within fields  40 – 44  using a mouse and/or keyboard  18 . Although not shown in  FIG. 3A , user interface  36  may also display and allow a user to change additional programmed parameters via fields similar to fields  40 – 44 , such as acceleration and decay constants. 
   Processor  30  also generates and displays current rate response curve values for the ADL range, which includes rates from the LR to the ADLR, and the exertion range, which includes rates from the ADLR to the USR. The rate response curve values correspond to and are generated based on the currently programmed setpoints retrieved from IMD  12 , which in turn correspond to the currently selected curve from the family of curves for each range. Although each family of curves stored by IMD  12  may include numerous curves, and thus the number setpoint values may be numerous, processor  30  may convert the setpoint values retrieved from IMD  12  for each range to one of ten curve values for each range in order to promote ease of understanding on the part of the user. Processor  30  may maintain look-up tables, or the like, within memory  38 , and use the look-up tables to determine a curve value based on a retrieved setpoint value. A greater curve value for a range corresponds to more aggressive rate response within the range. 
   In some embodiments, user interface  36  may display these curve values and allow a user to make changes to these values via fields of any type, such as a drop-down menus, text boxes, or drop-down menus with text boxes. The embodiment of user interface  36  illustrated in  FIGS. 3A–3F  displays these curve values and allows a user to make changes to the curve values via slider-bar fields  46  and  48 . The positions of the sliders  50  and  52  of each of slider-bar field  46  and  48  is set based on the curve value for that range. For example, as shown in  FIG. 3A , the positions both sliders  50  and  52  are set to 6, which are the current curve values for each range corresponding to the setpoint values received from IMD  12  for each range. A user may make changes to these curve values by moving sliders  50  and  52  or clicking on the arrow buttons provided with each slider-bar. The user may make these changes using, for example, a mouse associated with programmer  10 . 
   Processor  30  may also generate a current rate response curve  54  based on the rate limits and setpoint values retrieved from IMD  12 , and display current rate response curve  54  via rate response curve window  56 . As shown in  FIG. 3A , curve window  56  includes a two dimensional coordinate system for plotting sensor indicated rate (on the y-axis) as a function of activity level (on the x-axis). Processor  30  may display curve  54  by drawing a first line for the ADL range with a slope determined based on the currently programmed setpoint value for the ADL range received from IMD  12 . The curve value for this range, 6, is indicated on the graph near the first line. Processor  30  may then draw a second line for the exertion range with a slope determined based on the currently programmed setpoint value for the exertion range received from IMD  12 . The curve value for this range, 6, is also indicated on the graph, in this case near the second line. 
   The first line may be drawn from a point on the sensor indicated rate axis at the LR to a point defined by the setpoint value received for the ADL range and the ADLR. Another parameter that processor  30  may receive from IMD  12  is an ADL widthcounts value. Processor  30  may draw a horizontal line at the ADLR from the point corresponding to the setpoint value received for the ADL range and the ADLR from the point defined by the setpoint value received for the ADL range and the ADLR to a point defined by the setpoint value received for the ADL range plus the widthcounts value and the ADLR. The exertion response curve may be drawn from the point defined by the setpoint value received for the ADL range plus the widthcounts value and the ADLR to a point defined by the setpoint value received for the exertion range. Curve window  56  may, as shown in  FIG. 3A , include horizontal lines marking the LR, ADLR and USR, which may make curve  54  easier for a user to interpret. By displaying current rate response curve  54  via user interface  36 , programmer  10  may make it easier for a user to visualize the current rate response of IMD  12 . 
   As illustrated in  FIG. 3A , current rate response curve  54  may be drawn with solid lines. A pending rate response curve, which will be discussed in greater detail below, may be drawn with a different line format, such as a dashed line. 
   Where IMD  12  is capable of providing for optimization of rate response parameters, processor  30  may receive an indication from IMD  12  that indicates whether IMD  12  is currently operating in an optimization mode. Processor  30  may indicate to a user whether IMD  12  is currently operating in an optimization mode via a field  58 , as shown in  FIG. 3A . Field  58  may be a drop-down menu, text box, or drop-down menu with a text box, and a user may change the optimization mode of IMD  12  via field  58 . For example, a user may select whether rate response optimization is on or off via field  58 . 
   If rate response optimization is on, the user may direct processor  30  to display a target rate histogram window via user interface  36 , which will be described in greater detail below, instead of rate response curve window  56 . The user may select which window is displayed, via fields of any type provided by processor  30  within user interface  36 . For example, the user may select which window is displayed via a drop-down menu, text box, or drop-down menu with text boxes. The embodiment of user interface  36  illustrated in  FIGS. 3A–3F  includes button fields  60  and  62 , by which the user may select which window is displayed. The user may select a window by clicking one of button fields  60  and  62  using a mouse associated with programmer  10 . Processor  30  may make the target rate histogram window unavailable to the user when rate optimization is off because target rate histograms are generated based on optimization target values, as will be described in greater detail below. Processor  30  may make this feature of user interface  36  unavailable, by, for example, graying out button field  60  and/or not allowing the user to click on button field  60 . 
   As mentioned above, in addition to currently programmed parameters and optimization target values, processor  30  may retrieve data collected by IMD  12  from IMD  12 . Processor  30  may organize and format this data in a form suitable for display, and make this data available for display via user interface  36 . For example, IMD  12  may store data indicating the distributions of sensed and paced atrial beats within discrete rate ranges over time. Processor  30  may retrieve this data from IMD  12 , generate an atrial rate histogram that illustrates these distributions, and make this atrial rate histogram available for display via user interface  36 . 
   Other data that IMD  12  may collect and processor  30  may retrieve includes data indicating the distributions of sensed and paced ventricular beats within discrete rate ranges over time, data indicating the output of the sensors used to control the rate response of IMD  12  over time, and data indicating the distribution of actual sensor indicated rates within discrete rate ranges over time. Processor  30  may also generate histograms based on these categories of data, and make these histograms available for display via user interface  36 . 
   Processor  30  may provide one or more fields within user interface  36 , such as field  64  shown in  FIG. 3A , by which a user may direct processor  30  to display such a histogram. Field  64  may be a drop-down menu by which a user may select one of multiple available histograms for display, or a button by which a user may direct processor to display a single histogram, such as an atrial rate histogram. Processor  30  may display these histograms in a different window, or, in some embodiments, may display these histograms alongside a target rate histogram, which will be described in greater detail below. 
     FIG. 3B  illustrates user interface  36  when rate response optimization is on, and the user has directed processor  30  to display a target rate histogram window  64  by, for example, clicking button  60  as described above. As discussed above, processor  30  may, when rate response optimization is on, retrieve currently programmed optimization target values from IMD  12 . The optimization target values may be percentages of time that IMD  12 , through optimization, will cause the sensor indicated rate to be within particular ranges. Processor  30  may retrieve two current optimization target values, the current ADL percentage and current USR percentage, from some dual-slope embodiments of IMD  12 , as discussed above. 
   Using the currently programmed target values and rate limits, processor  30  generates a current target rate histogram  68 , and displays current target rate histogram  68  within target rate histogram window  64  of user interface  36 . Processor  30  may calculate, and current target rate histogram  68  may illustrate estimated percentages of time that IMD  12  will cause the sensor indicated rate to be within a number of discrete rate ranges, or bins, between the LR and USR based on the currently programmed optimization target values. By displaying current target rate histogram via user interface  36 , programmer  10  may make it easier for a user to visualize the current rate response of IMD  12 , and its effect on patient  14 . As shown in  FIG. 3C , processor may also display the current ADL percentage and current USR percentage with current target rate histogram  66  in histogram window  64 . 
   As shown in  FIG. 3B , target histogram window  66  includes a two dimensional coordinate system for plotting percentage of time (on the y-axis) as a function of sensor indicated rate (on the x-axis). In order to generate current target rate histogram  68 , the sensor indicated rate axis is divided into bins. The bins, as shown in  FIG. 3B , may be 10 beat-per-minute (b.p.m.) bins. However, bins of any size may be used. 
   Processor  30  calculates the percentage of time that IMD  12  will cause the sensor indicated rate to be within each bin via optimization based on the optimization target values and the rate limits. Processor  30  determines percentage of time in three rate ranges determined with reference to the rate limits, i.e., the ranges from the LR to the ADLR, from the ADLR to the USR, and at the USR, based on the optimization target values. For example, processor  30  identifies the bin that contains the USR, and calculates the percentage of time in that bin to be the USR percentage, i.e., the percentage of time that IMD  12  will cause the sensor indicated rate to be at the USR. Thus, if, as shown in  FIG. 3B , processor  30  retrieves a USR percentage target value of 0.4% from IMD  12 , processor  30  will assign 0.4% to the bin, from 120 b.p.m. to 130 b.p.m., that contains the USR, which is 120 b.p.m. 
   The ADL percentage is the percentage of time that IMD  12  will cause the sensor indicated rate to be within the range from the ADLR to the USR. Processor  30  will distribute the ADL percentage among the bins within this range. Processor  30  may distribute the ADL percentage among the bins by, for example, determining the number of bins within this range and estimating the fraction of the ADL percentage within each bin. Processor  30  may estimate the fraction of the ADL percentage within each bin using a variety of techniques, such as linear interpolation, non-linear, e.g., exponential interpolation, or by referring to a look-up table of percentages generated based on clinical data. Thus, if, as shown in  FIG. 3B , processor  30  retrieves an ADL percentage target value of 8% from IMD  12 , processor  30  may determine that there are two bins, from 100 b.p.m. to 110 b.p.m. and from 110 b.p.m. to 120 b.p.m., between the ADLR of 100 b.p.m. and the USR of 120 b.p.m., and use any of the above described techniques to assign a fraction of 8% to each of these bins. 
   Based on the ADL percentage, processor  30  may calculate the percentage of time remaining to be distributed amongst bins within the range from the LR to the ADLR. For example, if, as shown in  FIG. 3B , processor  30  retrieves an ADL percentage of 8% from IMD  12 , the percentage of time remaining for this range is 100%−8%, or 92%. Processor  30  may distribute this determined percentage of time among the bins within this range by, for example, determining the number of bins within this range and using any of the above-mentioned techniques to estimate the fraction of this below ADLR percentage within each bin. 
     FIG. 3C  illustrates user interface  36  after a user has made a change to a programmed parameter. In particular, as shown in  FIG. 3C , the user has manipulated slider-bar fields  46  and  48  to select different rate response curve values for the ADL range and the exertion range. The user has selected a more aggressive rate response within the ADL range than is currently programmed, and a less aggressive response in the exertion range. Slider-bar bar fields  46  and  48 , arrows, and buttons indicating “more” and “less” rate response provide an intuitive interface for a user to adjust rate response within these ranges, and are within the scope of this invention. Using such interfaces within user interface  36 , a user need not understand the relationship between rate response curve values and setpoint values used by IMD  12  in order to effectively adjust the rate response of IMD  12 . Thus user interface  36  may provide a user with a more intuitive to the user for programming or more or less aggressive rate response. 
   Based on the curve values selected by the user, e.g., the positions of sliders  50  and  52  within slider-bar fields  46  and  48 , processor  30  may determine pending setpoint values. Processor  30  may determine pending setpoint values by referring to a look-up table or the like stored within memory  38  that relates curve and setpoint values. Where a curve value selected by the user would lead to combination of setpoint values, i.e., a rate response, that is not capable of being implemented by IMD  12 , processor  30  may change the other curve value to achieve an allowed combination of setpoint values. Using the pending setpoint values and the unchanged currently programmed rate limits, processor  30  may generate and display a pending rate response curve  70  within curve window  54  in the manner described above with reference to the generation and display of current rate response curve  54 . 
   Pending rate response curve  70  illustrates what the rate response of IMD  12  would be using the pending parameters selected by the user. Thus, the user is able to evaluate the effect of reprogramming IMD  12  on the rate response of IMD  12  before actually reprogramming IMD  12 . As shown in  FIG. 3C , pending rate response curve  70  may be displayed via curve window  56  side-by-side with, e.g., at the same time as, current rate response curve  54 . By displaying current rate response curve  54  and pending rate response curve  70  side-by-side, programmer  10  may allow the user to more easily visualize the effect of the changes made to rate response parameters on the rate response of IMD  12 , making programming IMD  12  more intuitive for the user. Moreover, the user may evaluate the effect of these changes before submitting them to IMD  12 , i.e. without reprogramming IMD  12  with the changed parameters, and without an exercise test. Processor  30  may, as shown in  FIG. 3C , display current rate response curve  54  and pending rate response curve  70  with different line formats so that they may be more easily distinguished from each other. 
   Processor  30  may provide fields  72  and  74  within user interface  36  that allow a user to undo changes made to rate response parameters and accept changes made to rate response parameters respectively. Fields  72  and  74  may, as shown in  FIG. 3C , be button fields, and a user may use a mouse to click either of fields  72  and  74 . If the user clicks undo field  72 , processor  30  may remove pending rate response curve  70  from curve window  56 , and return sliders  50  and  52  to their original position. Processor may store currently programmed parameters, including the current programmed setpoint values and determined curve values, and pending parameters, including pending setpoint values and curve values, within memory  38  in order to facilitate this process. If the user clicks accept field  74 , processor  30  may reprogram IMD  12  with the pending parameters. 
     FIG. 3D  illustrates user interface  36  with target histogram window  64  displayed after a user has manipulated slider-bar fields  46  and  48  to select different rate response curve values for the ADL range and the exertion range, as described above. The user may have selected target histogram window  64  as described above after manipulating slider-bar fields  46  and  48  with curve window  56  displayed, or user may have manipulated slider-bar fields  46  and  48  with target histogram window displayed. 
   In either situation, when processor  30  receives a change or adjustment made by a user to either the ADL range or exertion range curve value, processor  30  may make a corresponding change or adjustment to the appropriate optimization target value, i.e., either the ADL percentage or the USR percentage. In other words, the user may make changes to the optimization target values via the ADL range and exertion range fields  46  and  48 . Processor  30  may refer to a look-up table or the like in stored in memory  38  to determine the pending optimization target value based on the input made by the user via fields  46  and  48 . The look-up table may include a number of possible values for the optimization targets, including the currently programmed target values. 
   If, for example, the user increments or decrements slider  50  by one position processor  30  may select the next greater or lesser ADL percentage value within a look-up table for ADL percentage values relative to the currently programmed ADL percentage value. If the next greater or lesser target value is not available, i.e., if the target is already at the highest or lowest possible value, processor  30  will continue to make changes to the curve value without changing the target value. In the example shown in  FIG. 3D , the user has incremented slider  50  of ADL range field  46  by two curve values, from the original curve value of 6 to a pending curve value of 8, and decremented slider  52  of exertion range field  48  by one curve value, from an original curve value of 6 to a pending curve value of 5. Processor  30  has selected a pending ADL percentage of 10%, which may have been two entries within a look-up table for ADL percentages greater than the current programmed ADL percentage of 8%, and a pending USR percentage of 0.3%, which may have been one entry within a look-up table for USR percentages less than the current programmed USR percentage of 0.4%. 
   When the user intends to change an optimization target value, the corresponding change in the rate response curve value, and thus the setpoint value, will advantageously bring the setpoint value closer to the value that IMD  12  would arrive at through optimization based on the changed optimization target values at the time of programming. Thus, the association of changes made to target values with changes to curve values in this manner will advantageously allow the patient to more quickly feel the effect of the changes when IMD  12  is reprogrammed with the changed setpoint values and optimization values. Further, this association will allow the user to more quickly evaluate whether the changes made are effective. 
   Using the pending target values and the unchanged rate limits, processor  30  may generate and display a pending target rate histogram  76  in the manner described above with reference to the generation of the current target rate histogram  66 . Pending target rate histogram  76  illustrates estimated percentages of time that IMD  12  would cause the sensor indicated rate to be within a number of discrete rate ranges using the pending optimization target values. Thus, the user is able to evaluate the effect of reprogramming IMD  12  on the rate response of IMD  12  before actually reprogramming IMD  12 . The user may reprogram IMD  12  or undo the pending changes via fields  74  and  72  of user interface  36 , as described above. 
   As shown in  FIG. 3D , pending target rate histogram  76  may be displayed via target histogram window  64  side-by-side with, e.g., at the same time as, current target rate histogram  66 . By displaying current target rate histogram  66  and pending target rate histogram  76  side-by-side, programmer  10  may allow the user to more easily visualize the effect of the changes made to optimization target values on the rate response of IMD  12 , making programming IMD  12  more intuitive for the user. Moreover, the user may evaluate the effect of these changes before submitting them to IMD  12 , i.e. without reprogramming IMD  12  with the changed parameters, and without an exercise test. Processor  30  may, as shown in  FIG. 3D , display current target rate histogram  66  and pending target rate histogram  86  with different shading so that they may be more easily distinguished from each other. 
     FIGS. 3E and 3F  illustrate user interface  36  with rate response curve window  56  and target rate histogram window  66  displayed, respectively, after a user has modified additional programmed parameters, such as the rate limits within fields  40 – 44 . Although  FIGS. 3E and 3F  illustrate these modifications to rate limits in addition to modifications to curve values and optimization target values made via ADL range and exertion range fields  46  and  48 , it is to be understood that these modifications to rate limits may be made in the absence of other modifications to the programming of IMD  12 . Further, although  FIGS. 3E and 3F  illustrate these modifications only to rate limits within fields  40  and  44 , it is to be understood that the rate limit of field  42  may also be modified. In other words, a user may modify any one of or combination of currently programmed parameters, current rate response curve values, or currently programmed optimization target values displayed via user interface  36  consistent with the invention. 
   In the example illustrated by  FIGS. 3E and 3F , the user has modified the LR within field  40  from the currently programmed value of 60 b.p.m. to a pending value of 50 b.p.m., and the USR within field  44  from the currently programmed value of 120 b.p.m. to a pending value of 140 b.p.m. As shown in  FIGS. 3E and 3F , fields  40  and  44  may be shaded or the like to indicate that they are currently displaying pending values. As shown in  FIG. 3E , based on the pending rate limits and the pending setpoint values that were discussed above with reference to  FIG. 3C , processor  30  may generate and display a pending rate response curve  78  in the manner discussed above. Further, as shown in  FIG. 3F , based on the pending rate limits and the pending optimization target values that were discussed above with reference to  FIG. 3D , processor  30  may generate and display a pending target rate histogram  80  in the manner discussed above. Display of the pending curve  78  and histogram  80 , and display of the pending curve  78  and histogram  80  alongside a current curve  54  and histogram  66  respectively may provide the advantages discussed above. Further, the user may reprogram IMD  12  or undo the pending changes via fields  74  and  72  of user interface  36 , as described above. 
     FIG. 4  is a flow diagram illustrating an exemplary method for programming a rate responsive IMD, such as IMD  12 , via programmer  10  and user interface  36 . Processor  30  of programmer  10  interrogates IMD  12  ( 90 ) to retrieve currently programmed parameters ( 92 ). Where IMD  12  is in an optimization mode, processor  30  may also retrieve currently programmed optimization target values. Processor  30  may also retrieve data collected by IMD  12  and stored within a memory of IMD  12 , as described above. Processor  30  may interrogate IMD  12  via transceiver  32  and antenna  34 , which may correspond to a programming head of programmer  10  placed over IMD  12 . 
   Processor  30  displays the at least some of the currently programmed parameters to a user via user interface  36  ( 94 ). The currently programmed parameters displayed via user interface  36  may include rate limits, such as the LR, ADLR and USR, and may also include acceleration and decay constants. The currently programmed parameters may be displayed via fields of user interface  36 , such as fields  40 – 44 . The currently programmed parameters may also include one or more currently programmed setpoint values described above, and processor  30  may determine and display current curve values, such as an ADL range curve value and an exertion curve value, based on the setpoint values. The curve values may be displayed via fields of user interface  36  such as slider-bar fields  46  and  48 . Where IMD  12  is in an optimization mode, processor  30  may also display currently programmed optimization target values. 
   Processor  30  generates a current rate response curve  54  based on the currently programmed parameters, e.g., the rate limits and setpoint values retrieved from IMD  12 , and display current rate response curve  54  to a user via user interface  36  ( 96 ). Where IMD  12  is in an optimization mode, processor  30  may generate a current target rate histogram  66  based on the rate limits and the currently programmed optimization target values, and display current target rate histogram  66  via user interface  36 , as discussed above. The curve  54  and histogram  66  may be presented via different windows provided by user interface  36 , and a user may select which window processor  30  will display via fields within user interface  36 , such as button fields  70  and  72 , as discussed above. By displaying current curve  54  and current histogram  66 , programmer  10  enables a user to better visualize the effect of the current programming of IMD  12  on the rate response of IMD  12 . 
   The user may make changes to the currently programmed rate response parameters, current curve values, or currently programmed optimization target values displayed via user interface  36  by interacting with fields of user interface  36  that contain these values, and processor  30  may display these changes ( 98 ). Processor  30  may provide fields within user interface  36 , such as slider-bar fields  46  and  48 , that allow the user to change both a curve value and a target value by a single action, as described above. The use of slider-bar fields  46  and  48 , or similar fields, allows the user to intuitively increase or decrease the aggressiveness of the rate response of IMD  12  within a range. The changing of a curve value when changing a target value brings the pending parameters closer to the values that IMD  12  would arrive at through optimization. When IMD  12  is programmed with these parameters patient  14  may more quickly feel the benefit of the changes, the user may more quickly evaluate the effect of these changes. 
   Processor  30  generates and displays a pending rate response curve  70 , 78  via user interface  36  based on the pending parameters and the unchanged currently programmed parameters, and may, if IMD  12  is in an optimization mode, generate and display a pending target rate histogram  76 , 80  via user interface  36  based on the pending parameters or target values, and the unchanged currently programmed parameters or target values ( 100 ). Processor  30  may display current and pending curves and histograms via user interface side-by-side, allowing the user to more easily visualize the effect of the changes made programmed parameters or optimization target values on the rate response of IMD  12 , making programming IMD  12  more intuitive for the user, and allowing the user to evaluate the effect of these changes before reprogramming IMD  12 , and without an exercise test. 
   If the user accepts the changes made via user interface  36  ( 102 ), processor  30  may reprogram IMD  12  with the pending parameters or target values replacing currently programmed parameters or optimization target values ( 104 ). If the user does not accept the pending parameters ( 102 ), processor  30  may reset user interface  36  with currently programmed parameters, and/or wait to receive more changes made by the user via user interface  36  ( 98 ). Processor  30  may provide fields within user interface  36 , such as button fields  70  and  72 , that allow a user to accept or undo pending parameters or target values. 
     FIG. 5  is a flow diagram illustrating an exemplary method for providing current and pending rate response curves. The currently programmed parameters retrieved from IMD  12  may include current rate limits, such as the LR, ADLR and USR, and current setpoint values, such as an ADL and an exertion setpoint value ( 110 ). Processor  30  identifies current ADL and exertion curve values based on the currently programmed setpoint values ( 112 ). Processor  30  may refer to look-up tables or the like within memory  38  to determine a curve value based on a retrieved setpoint value. Processor  30  then sets ADL range and exertion range fields  46  and  48  within user interface  36  to the current ADL and exertion curve values ( 114 ). Fields  46  and  48  may be slider-bar fields, and may include sliders  50  and  52  positioned according to the current curve values. 
   Processor  30  also generates and displays a current rate response curve  54  based on the rate limits and setpoint values retrieved from IMD  12  ( 116 ), receives parameter changes ( 118 ), and displays a pending rate response curve based on the pending parameters ( 120 ). Where the user makes a change to a curve value by manipulating one of curve value fields  46  and  48 , processor  30  will determine a pending setpoint value based on the new curve value so that the pending rate response curve may be generated. Processor  30  may refer to look-up tables or the like within memory  38  to determine a setpoint value based on the new curve value. Moreover, the processor  30  will use the determined pending setpoint value to reprogram IMD  12  if the user accepts the changes made. 
     FIG. 6  is a flow diagram illustrating an exemplary method for generating a current or pending target rate histogram. Processor  30  determines current or pending programmed rate limits, such as the LR, ADLR and USR, and current or pending programmed optimization target values, such as the ADL percentage and the USR percentage ( 130 ). Processor  30  may retrieve current programmed rate limits and currently programmed target values from IMD  12  to generate a current target rate histogram, and may receive pending rate limits and/or target values from a user via user interface  36  to generate a pending target rate histogram based on the pending limits or values, and the unchanged limits or values. Processor  30  generates a current or pending target histogram by estimating percentages of time that IMD  12  will cause the sensor indicated rate to be within a number of discrete rate ranges, or bins, between the LR and the USR via optimization. Processor  30  estimates these percentages based on optimization target values, such as the ADL percentage and USR percentage, that are percentages of time that IMD  12  will cause the sensor indicated rate to be within subsets of the range from the LR to the USR via optimizations. The bins may be 10 b.p.m bins. 
   Processor  30  assigns the USR percentage, which is the percentage of time IMD  12  will cause the sensor indicated rate to be at the USR, to the bin containing the USR ( 132 ). Processor  30  also determines the number of bins between the ADLR and the USR ( 134 ), and distributes the ADL percentage, which is the percentage of time IMD  12  will cause the sensor indicated rate to be between the ADLR and the USR via optimization, among these bins, by, for example, using linear or non-linear interpolation, or by referring to a look-up table of percentages generated based on clinical data, to determine the fraction of the ADL percentage to assign to each bin ( 136 ). Processor  30  also determines the percentage of time that IMD  12  will cause the sensor indicated rate to be within the remainder of the rate range between the LR and the USR, i.e., the rate range between the LR and the ADLR by subtracting the ADL percentage from 100% ( 138 ), determines the number of bins within this range ( 140 ), and distributes the determined percentage of time among the determined bins by, for example, using the above-mentioned techniques to determine the fraction of the determined percentage to assign to each bin ( 142 ). 
     FIG. 7  is a flow diagram illustrating an exemplary method for adjusting rate response curve values and optimization target values based on user interaction with rate response curve value fields  46  and  48  of user interface  36 . Fields  46  and  48  may be slider-bar fields, as described above. When processor  30  receives a change or adjustment made by a user to either the ADL range or exertion range curve value fields  46  and  48  ( 150 ), processor  30  will generate a pending rate response curve based on the new curve value ( 152 ). The user may change the curve value by moving a slider  50  or  52  of field  46  or  48 . Processor  30  may generate the pending rate response curve by determining a corresponding pending setpoint value and generating the curve based on the pending setpoint value, as described above. 
   When the user changes the curve value, if IMD  12  is in an optimization mode ( 154 ), processor  30  may determine whether a corresponding change to the appropriate optimization target value, i.e., either the ADL percentage or the USR percentage, is available ( 156 ). Processor  30  may refer to a look-up table or the like in stored in memory  38  of IMD  12  to determine the pending optimization target value based on the input made by the user via fields  46  and  48 , e.g., by traversing the look-up table from the currently programmed target value based on the number of curve values or slider positions of the change made by the user, as described above. If a target value within the table corresponding to the user input is available, processor  30  will display the pending target value and generate a pending target rate histogram based on the pending target value ( 158 ). If the input made by the user exceeds the upper or lower limit of the look-up table, processor  30  may not make the change and display the current target value and current target rate histogram, or may display as the pending target value the maximum or minimum target value and display the pending target rate histogram based on the maximum or minimum target value ( 160 ). 
   As described above, associating changes in optimization target values with changes in rate response curve values, and thus the setpoint values, will advantageously bring the setpoint values closer to the values that IMD  12  would arrive at through optimization based on the changed optimization target values at the time of programming. Thus, the association of changes made to target values with changes to curve values in this manner will advantageously allow the patient to more quickly feel the effect of the changes when IMD  12  is reprogrammed with the changed setpoint values and optimization values. Further, this association will allow the user to more quickly evaluate whether the changes made are effective. 
   Various embodiments of the invention have been described. It is to be understood, however, that in light of this disclosure, other embodiments will become apparent to those skilled in the art. For example, programmer  10  may be embodied in any type of computing device, such as a handheld computer, laptop computer, desktop computer, workstation, or the like. In some embodiments, programmer  10  may interact with IMD  12  remotely via a computer network. 
   Although optimization target values have been described herein as percentages of time, the invention is not so limited. Optimization target values may be expressed as times per day, week, month, or the like for the sensor indicated rate to be within a particular rate range, and IMD  12  may optimize the rate response to achieve these targets. A target rate histogram generated based on such a optimization target value would estimate an amount of time per day, week, month, or the like that IMD  12  would cause the sensor indicated rate to be within each bin. Accordingly, these and other embodiments are within the scope of the following claims.