WO2008121110A1

WO2008121110A1 - Methods and apparatus for monitoring battery charge depletion

Info

Publication number: WO2008121110A1
Application number: PCT/US2007/008208
Authority: WO
Inventors: Shay M. Vaingast
Original assignee: Ams Research Corporation
Priority date: 2007-03-30
Filing date: 2007-03-30
Publication date: 2008-10-09

Abstract

A system and method of monitoring the amount of charge consumed from a battery powering a device, e.g., an implantable medical device, operable in at least first and second current drain states are disclosed. In each drain state, the duration of the state is timed out as a state time. At each state change, the state time is added to cumulative state time for the current drain state. A cumulative charge drawn from the battery in each current drain state can be calculated as a function of the state current drain and the cumulative state time for the current drain state. The amount of charge consumed from the battery is represented by the cumulative charge drawn in all of the current drain states. The calculations of the amount of charge consumed can take place in the implantable medical device or in an external medical device interrogating data stored in the implantable medical device.

Description

METHODS AND APPARATUS FOR MONITORING BATTERY CHARGE DEPLETION

FIELD

[0001] The present invention pertains to methods and apparatus for monitoring a battery of a device, particularly the battery of an implantable medical device, enabling estimation of the depletion of and/or the remaining battery charge and remaining battery life.

BACKGROUND

[0002] As stated in U.S. Patent Nos. 6,671 ,552 and 6,901 ,293, a wide variety of implantable medical devices (IMDs) are commercially released or proposed for clinical implantation that are programmable in a variety of operating modes and are interrogatable using RF telemetry transmissions. Such IMDs include cardiac pacemakers, pacemaker/cardioverter/defibrillators, now referred to as implantable cardioverter-defibrillators (ICDs), cardiomyostimulators, other electrical stimulators including nerve and muscle stimulators, deep brain stimulators, and cochlear implants, drug delivery systems, cardiac and other physiologic monitors, and heart assist devices or pumps, etc. Such IMDs other than monitors and drug delivery systems comprise an implantable pulse generator (IPG) and one or more electrical medical lead coupled to a connector of the IPG bearing body signal sense and/or stimulation electrodes and/or physiologic sensors for detecting a condition of the body, a body organ or other body tissue. The IPG typically comprises a hermetically sealed housing enclosing at least one battery and electronic circuitry powered by the battery that processes input signals, provides electrical stimulation and communicates via uplink . and downlink telemetry transmissions with an external medical device, typically a programmer that is capable of being used to alter an IPG operating mode or parameter. The current drawn from the battery or batteries varies in relation to the IPG operating state, e.g., during sensing or stimulating time periods.

[0003] Typical batteries used in powering IMDs other than the cardioversion/defibrillation shock delivery circuitry of ICDs comprise lithium- iodine batteries having discharge characteristics described in U.S. Patent No. 6,167,309, for example, and lithium/carbon monofluoride batteries having discharge characteristics described in U.S. Patent No. 6,108,579, for example. It is well known that a battery's internal impedance increases with time and usage resulting in a decrease in battery terminal voltage. The voltage drop across the battery's internal impedance, which tends to act like a voltage divider circuit, increases as the internal impedance increases. The decrease in terminal voltage eventually reaches a battery "end of life" (EOL) voltage that is insufficient to power the IMD. The discharge characteristics of batteries can be expressed by curves (or equations) of internal battery impedance as a function of expended battery capacity (in terms of charge).

[0004] As noted in the above-referenced ^"552 patent, typically IPGs and monitors are designed to monitor the level of battery depletion and to provide some indication when the depletion reaches a level at which the IPG or monitor should be replaced. For example, pacing IPGs typically monitor battery energy and depletion and develop an "elective replacement indicator" (ERI) when the battery depletion reaches a level such that replacement will soon be needed to avoid further depletion to the EOL voltage. Operating circuitry in the pacing IPG typically responds to issuance of an ERI by switching or deactivating operating modes to lower power consumption in order to maximize the ERI-to-EOL interval, referred to in certain instances as an elective replacement time (ERT) or recommended replacement time (RRT) during which the IPG or monitor should be replaced.

[0005] In the above-referenced '552 patent, the IPG periodically makes and stores battery voltage measurements and accumulates incident (stimulation) counts, sense and stimulation channel impedance measurements, and current drain indication data that is periodically uplink telemetry transmitted during a telemetry session to an external programmer for display and analysis. A complex process is followed in the external programmer to compute an estimated past current drain (EPCD). The EPCD is the estimated average current drain from the time of the most recent past computation to the present time of computation or a shorter time period. The programmer then computes a remaining life estimate (RLE, aka as the ERT) to EOL based on the average battery voltage and EPCD.

[0006] Alternative and simpler approaches to determining an ERT or to simply determine battery charge depletion have been proposed or implemented in IPGs over the years employing measurements of battery impedance and/or current drain and known battery characteristics.

[0007] As described in U.S. Patent No. 6,748,273, monitoring the internal impedance of the battery and comparing it to characteristic battery impedance changes during discharge is considered to be a reliable way of determining the remaining capacity and ERT of the battery. However, certain fresh batteries exhibit a low, substantially constant, internal impedance a corresponding stable voltage for a comparatively long time, and it is difficult to perform reliable measurements of the small changes in internal impedance during this time. Further U.S. Pat. No. 5,370,668 discloses an IMD in which internal battery impedance measurements are combined with periodic assessments of the loaded terminal voltage of the battery to trigger an ERI and establish an ERT. The technique disclosed in the '668 patent is adapted particularly for rejecting transients in the battery's demand as criteria for triggering an ERI.

[0008] The '273 patent also indicates that from a theoretical point of view the ideal way of determining the remaining capacity of a battery would be measurement of the charge drawn from the battery as disclosed in U.S. Pat. Nos. 4,715,381 , and 5,769,873, for example. In the above-referenced "273 patent, battery impedance is measured and an impedance-based value of the remaining capacity of the battery is determined from a detected impedance increase. An analysis of the battery impedance increase is performed to determine whether the battery impedance is a reliable indicator of the remaining battery capacity and, if not, the total charge depleted from the battery is measured, and a charge depletion-based value of the remaining capacity of the battery is determined. [0009] In the '381 patent, an IPG battery test circuit is disclosed for quantifying the consumed charge from the number of stimulation pulses emitted and from the expended pulse charge. Other losses of current, like e.g. leakage currents, are not considered. The true remaining battery capacity could then be less than the estimated remaining capacity and consequently the remaining operation time could be overestimated.

[0010] In a further U.S. Patent No. 5,193,538, the depletion of a pacemaker

IPG battery is monitored to determine the ERT before battery voltage further depletes to the EOL voltage. The battery voltage is periodically compared to a reference or threshold voltage characterized as an ERT-value that is less than full battery voltage at beginning of life (BOL) and selected to provide an ERT of about three months to EOL. It is recognized that the rate of battery voltage depletion is dependent upon the rate at which battery charge or current is consumed in any given "stimulating mode", which appears to reference either or both of a pacing mode and pacing parameters in a given pacing mode. Stimulating modes may include a fixed rate pacing mode or a demand pacing mode of the types referenced in the Inter-Society Commission for Heart Disease Resource Code published by the American Journal of Cardiology. 34, 487, 1974 and those subsequently implemented in pacing, cardioversion, and defibrillation. In a given pacing mode, the rate of battery depletion depends on the physician programmed pacing parameters, including pulse voltage and pulse width as well as pacing rate, as well as the utilization or percentage of time that pacing is not inhibited when the patient's underlying heart rate exceeds the programmed pacing interval.

[0011] The solution proposed in the '538 patent appears to involve varying the

ERT-value in dependence on the utilized stimulating mode and in dependence on the degree of utilization of previously selected stimulating modes recorded in and available from stimulating mode selector means. A higher threshold value is selected for stimulating modes with higher energy consumption and a higher degree of utilization and a lower threshold value is selected for stimulating modes with a lower energy consumption and a lower degree of utilization. Thus, an adaptation and stabilization of the ERT between the satisfaction of the ERT-value and the point in time of the EOL- value is achieved according to the utilized stimulating mode, which deviates from an assumed standard stimulating mode.

[0012] However, this solution requires current consuming, current sources or loads to establish the ERT-values and rather precise estimations of utilization or pace pulse counts to select the same to set a current ERT-value that may provide a relatively constant ERT to EOL. Also, current sources may not be stable over extended time periods.

[0013] In U.S. Patent Nos. 4,556,061 , 5,769,873 and 6,885,894, a measurement of charge depletion is provided not by measuring the voltage level or impedance of the pacemaker IPG battery, but rather by continuously measuring the electrical current drawn from the battery and integrating that measured current over an integration time period. A precision current-sensing resistor in series with the positive side of the battery provides a sense signal having a voltage that varies according to the magnitude of current being drawn during stimulation and sensing. The sense signal is integrated using a voltage-controlled oscillator (VCO) circuit and counter, which are implemented using CMOS circuitry arranged in a switched-capacitor topology. The VCO signal is in the form of a pulse sequence, where each pulse has a duration corresponding to a discrete quantity of depleted charge. The counter counts the VCO pulses to produce the measurement of the depleted charge.

[0014] The current drawn by the IPG circuitry of the ^"061 , "873, and 894 patents varies as a function of the instantaneous operating state, and the voltage developed across the current-sensing resistor varies as a function of the current drawn by the pacing circuitry powered by the battery. The current passing through the current-sensing resistor in the interval between pacing pulses is relatively low, resulting in a relatively low voltage drop, and is relatively high during recharge of an output capacitor following its discharge to deliver a pacing pulse, resulting in a relatively high voltage drop. In order to operate the VCO during low current drain intervals between pacing pulses, it may be necessary to select a relatively high current-sensing resistor resistance. Then, during high current drain intervals, the voltage drop across the current-sensing resistor will reduce the voltage available to power the IPG circuitry. The reliability of circuit operations may become of concern during such high current drain intervals and as battery voltage depletes over time.

SUMMARY

[0015] The preferred embodiments of the present invention incorporate a number of inventive features that provide a simple and accurate measurement of charge depletion of a battery powering a device, e.g., an IMD, without itself unduly loading the battery while minimizing battery charge depletion.

[0016] In accordance with one embodiment of the present invention, a system and method of monitoring the amount of charge consumed from a battery powering a device, e.g., an implantable medical device, operable in at least first and second current drain states are provided. The duration of each operating state is timed out as a state time. At each state change, the state time is added to cumulative state time for the current drain state. A cumulative charge drawn from the battery in each current drain state can be calculated as a function of the current drain of the state and the cumulative state time. The total amount of charge drawn from the battery is represented by the sum of the cumulative charges of all of the current drain states. The calculations of the current drain state cumulative charges and/or the total charge consumed can take place in the implantable medical device or in an external medical device interrogating data stored in the implantable medical device.

[0017] A charge state of the battery, e.g., the total charge drawn from the battery or the remaining battery charge, can be calculated either in the implantable or the external medical device as a function of the cumulative charges drawn in all of the current drain states and the known battery capacity. Similarly, an ERT of the battery can be estimated either in the implantable or external medical device from the charge state of the battery, average rate of charge depletion, and the known capacity and depletion characteristics of the battery. [0018] This summary of the invention has been presented here simply to point out some of the ways that the invention overcomes difficulties presented in the prior art and to distinguish the invention from the prior art and is not intended to operate in any manner as a limitation on the interpretation of claims that are presented initially in the patent application and that are ultimately granted.

BRIEF DESCRIPTION OF THE DRAWINGS

[0019] These and other advantages and features of the present invention will be more readily understood from the following detailed description of the preferred embodiments thereof, when considered in conjunction with the drawings, in which like reference numerals indicate identical structures throughout the several views, and wherein:

[0020] FIG. 1 is a simplified schematic diagram of a battery powered IMD adapted to be implanted in a patient's body incorporating the ability to provide the physician with the measure of total charge drawn from the battery from which an estimation of battery remaining life may be made; and

[0021] FIG. 2 is a flow chart illustrating the steps of operating the IMD of FIG.

1 to provide a measure of total charge drawn from the battery from which an estimation of battery remaining life may be made.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0022] In the following detailed description, references are made to illustrative embodiments of methods and apparatus for carrying out the invention. It is understood that other embodiments can be utilized without departing from the scope of the invention. Preferred methods and apparatus are described for IMDs adapted to be implanted in a patient's body and operable or interrogatable employing an external programmer.

[0023] The charge drain monitoring circuitry and software of the present invention can be embodied in battery powered IPGs adapted to apply electrical stimulation through electrical medical leads to pelvic floor muscles and/or nerves to alleviate incontinence. [0024] Incontinence is a condition characterized by involuntary loss of urine, beyond the individual's control, that results in the loss or diminution of the ability to maintain the urethral sphincter closed as the bladder fills with urine. Male or female stress urinary incontinence (SUI) occurs when the patient is physically or emotionally stressed.

[0025] One cause for this condition is damage to the urethral sphincter or loss of support of the urethral sphincter, such as can occur in males after prostatectomy or following radiation treatment, or that can occur due to pelvic accidents and aging related deterioration of muscle and connective tissue supporting the urethra. Other causes of male incontinence include bladder instability, over-flowing incontinence and fistulas.

[0026] The female's natural support system for the urethra is a hammock-like supportive layer composed of endopelvic fascia, the anterior vaginal wall, and the arcus tendineus (a distal attachment to the pubic bone). Weakening and elongation of the pubourethral ligaments and the arcus tendineus fascia pelvis, weakening of the endopelvic fascia and pubourethral prolapse of the anterior vaginal wall, and their complex interaction with intraabdominal forces are all suspected to play a role in the loss of pelvic support for the urethra and subsequent hypermobility to an unnaturally low non-anatomic position, leading to urinary incontinence.

[0027] Exemplary IMDs for treatment of urinary incontinence and neurogenic bladder dysfunction are disclosed, for example, in Biocontrol Medical Ltd. U.S. Patent Nos. 6,354,991 , 6,652,449, 6,712,772, and 6,862,480. The IMDs disclosed in the '991, ^"449, and '480 patents for treatment of both urinary stress incontinence and urge incontinence comprise a control unit (IPG) and electrical medical leads bearing one or more sensing/stimulation electrode and one or more physiologic sensor adapted to be implanted in selected sites of a patient's body. The sensing/stimulation electrode(s) is preferably implanted in the pelvic region of a patient so as to be in electrical contact with body tissue including one or more of the muscles that relax and contract in regulating urine flow from the bladder. The control unit is preferably implanted under the skin of the abdomen or genital region, and receives signals from the electrodes and/or from the sensors. Motion and/or pressure signals detected by the physiologic sensor(s) and/or electromyogram (EMG) signals appearing across the sensing/stimulation electrodes are conveyed to and analyzed by the control unit operating system in order to distinguish between signals indicative of urge incontinence and those indicative of stress incontinence. A particular pressure sensor design is disclosed in the above-referenced T72 patent. When impending stress incontinence is detected, the control unit generates and provides an electrical stimulation therapy having stimulation parameters configured to treat stress incontinence through the electrodes to the tissue. Similarly, urge incontinence is treated with intermittent electrical stimulation having stimulation parameters configured to treat urge incontinence.

[0028] In various configurations, the IMDs disclosed in the above-referenced

Biocontrol Medical patents may be used alternatively or additionally to treat fecal incontinence, interstitial cystitis, urine retention, or other sources of pelvic dysfunction, pain or discomfort, by suitable modifications to the IMD.

[0029] Such an IMD adapted to deliver stimulation therapies in the pelvic region to treat such disorders is schematically depicted in FIG. 1 comprising an IPG 100 (within the dotted lines) coupled with electrical medical leads 140 and 150 implanted in a patient's body. The IPG 100 comprises a hermetically sealed housing 102 enclosing schematically depicted components of an IPG operating system and having an IPG connector 110 for making connection with proximal lead connectors of the electrical medical leads 140 and 150. It will be understood that the electrical medical leads 140 and 150 may be combined into a single electrical medical lead.

[0030] As indicated in the above-referenced Biocontrol Medical patents, physiologic sensors that generate signals responsive to, for example, motion, intravesical or abdominal pressure, or urine volume in the bladder may be useful in indicating some forms of incontinence. Typically, when the urine volume in the bladder is low, there will be no urine flow even when the abdominal pressure does increase. As described in detail, the control unit preferably processes the signals from the various sensors and uses them to determine when the electrical stimulation should be applied to the muscles to inhibit urine flow.

[0031] In FIG. 1 , the physiologic sensor is denoted as a pressure sensor 142 supported in the body by the electrical medical lead 140. Electrical medical lead 140 comprises at least one electrically insulated conductor extending between a distal pressure sensor 142, for example, and a proximal lead connector adapted to be coupled to the IPG connector 110 in a manner well known in the art. The pressure sensor 142 may take the form of the pressure sensor disclosed in the above-referenced Biocontrol Medical patents, particularly the above-referenced T72 patent.

[0032] The electrical medical lead 150 delivers electrical stimulation and preferably senses the EMG and may be configured as a unipolar, bipolar or multi-polar lead. A unipolar lead 150 comprises one electrically insulated conductor extending between one distal sensing/stimulation electrode and a proximal lead connector adapted to be coupled to the IPG connector 110 in a manner well known in the art. A bipolar or multi-polar lead 150 comprises at least two electrically insulated conductors extending between spaced apart distal sensing/stimulation electrodes 152 and a proximal lead connector adapted to be coupled to an IPG connector 110 in a manner well known in the art. Leads 140 and 150 may be combined into a single electrical medical lead or the pressure sensing lead 140 may also be configured to provide electrical sensing and/or stimulation.

[0033] As described in the above-referenced Biocontrol Medical patents, the lead bodies of the electrical medical leads 140 and 150 may be about 5 — 10 cm long. The sensing/stimulation electrode(s) 152 are preferably formed of platinum-iridium or nickel-chromium alloy and may be in the shape of flexible, intramuscular-type, wire electrodes that may be about 1-5 long and 50-100 microns in diameter to minimize patient discomfort. It will be understood that a fixation mechanism may be incorporated into the lead bodies of the electrical medical leads 140 and 150 to retain the pressure sensor 142 and/or sensing/stimulation electrode(s) 152 at selected sites. For example, the sensing/stimulation electrodes 142 may be formed in the shape of a spiral or hook, as is known in the art, so that they can be easily and permanently anchored in the muscle. The IPG 100 and lead 150 may provide unipolar or bipolar stimulation of the body tissue in locations disclosed in the above- referenced Biocontrol Medical patents, for example. Particular techniques for implanting the leads 140 and 150 or an electrical medical lead combining the physiologic sensor with the sensing/stimulation electrodes are disclosed in the above-referenced Biocontrol Medical patents.

[0034] As shown in FIG. 1, the sensing/stimulation electrode(s) 152 of lead

150 are coupled by lead conductors and the IPG connector 110 to the ACTIVE and indifferent (IND) input(s) of an EMG processing circuit 104. If the IPG 100 is configured for unipolar sensing and stimulation, then the IND input/output line is coupled to the conductive housing 102 encasing the components of the IPG100 other than the IPG connector 110 and, in certain cases, the antenna 120. The EMG processing circuit 116 may simply take the form of an amplification stage that outputs the EMG signal for reasons explained in the above-referenced Biocontrol Medical patents.

[0035] The sensing/stimulation electrode(s) 152 of lead 150 are also coupled by the lead conductors through the IPG connector 110 to the output(s) of the stimulation generating circuit 106. As described in the above-referenced Biocontrol Medical patents, stimulation generating circuit 106 comprises a DC/DC converter, as is known in the art, and a capacitor, which is charged by the DC/DC converter to a stepped-up voltage level VCAP regardless of the precise battery voltage of battery 112, which may vary between 3.2 and 2.2 - 2.5 volts. The same DC/DC converter, or another similar device, preferably supplies power to other circuit components of IPG 100. The stepped up voltage is discharged through the sensing/stimulation electrodes to stimulate tissue.

[0036] Operating modes and parameters of the IPG operating system may be interrogated or programmed using the external medical device 200. Optionally, the patient may be provided with a magnet 230 that the patient may apply against the skin overlying the IPG 100 to close a reed switch 132 of the IPG 100 to either trigger or inhibit delivery of electrical stimulation, depending on the nature of the therapy. For example, the operating system may respond to the magnetic field induced reed switch closure to inhibit delivery of electrical stimulation so the patient may voluntarily void.

[0037] The external medical device 200 may take the form of a personal computer having a display, printer, memory, an input device, e.g., a keyboard and mouse or screen pointer, an output coupled to the world-wide web, a CPU, and be controlled by hardware, firmware and software that enables two- way telemetry communication with the IPG 100. The external medical device 200 may be a programmer provided to the physician treating the patient for use when the patient is present. A limited function external medical device 200 may be provided to the patient to provide the patient with the ability to increase or decrease the intensity and/or duration of the stimulation. In addition, the limited function external medical device provided to the patient may also comprise a telemetry transceiver having the capability of receiving remotely transmitted commands from a medical center to generate and transmit the UT DATA command, receive the computed value of the total charge Q drawn from the battery and/or the cumulative state times ST-TIMEi - ST-TIME_N, and communicate the data to the remote medical center. In either case, the telemetry communication link may take any of the known forms that provide uplink telemetry (UT) and downlink telemetry (DT) transmissions between IPG 100 and external medical device 200 transmitted between IPG antenna 120 and antenna 220, respectively, through the patient's skin. Any of the IMD/programmer telemetry protocols and formats may be employed.

[0038] The IPG 100 may take any of the known forms that can be programmed using the external medical device 200 to provide therapy stimulation taking the form of single pulses or pulse bursts separated by interpulse periods, wherein the pulse energy, including pulse width and amplitude, and the burst frequency, number of pulses in the burst, and the interpulse period may be remotely programmed by a physician employing external medical device 200. A number of stimulation regimens for treating various forms of incontinence are set forth in the above-referenced Biocontrol Medical patents. Generally speaking, a stimulation cycle of the type described above with respect to FIG. 1 is established involving repetitive state changes between low, medium and high current drain states. The stimulation generating circuit 106 draws charge from the battery 112 to generate the stimulation regimen dictated by the IPG operating system, particularly the operating system algorithm embodied in memory, firmware and software within the micro-controller unit (MCU) based control and timing circuit 116. The MCU-based control and timing circuit 116 times out the operating states/current drain states of a given stimulation cycle and triggers state changes either on time-out or when interrupted by changes in input signals, including processed changes in pressure and EMG signals.

[0039] As noted above, stimulation may be inhibited by the output signal

RS_OU_T of a reed switch circuit 130 when the patient closes the reed switch 132. The inhibition signal R-S INHIBIT may persist to interrupt the high current drain, stimulation delivery state for a time period set by the MCU- based control and timing circuit 116. Alternatively, the reed switch 132 may be directly incorporated into the stimulation generating circuit 106 to directly inhibit stimulation when the magnetic field closes (or opens) the reed switch 132.

[0040] The MCU-based control and timing circuit 116 comprises one or more signal amplifier, A/D converter, and D/A converter as well as RAM registers for temporary and permanent data storage, counters, data buses, and interconnecting circuits. As described below, the MCU-based control and timing circuit 116 also comprises a CPU able to be driven by low-speed and high-speed clocks. A mixture of hardware, firmware and software processes the operating algorithm with operating parameters programmed into RAM employing the external medical device 200 and the telemetry I/O transceiver 118 operating in the fashion of telemetry transceiver 118 described above. A watchdog circuit 126 monitors the status of the system and resets the system to a start-up state if an error is detected. [0041] The control and timing circuit 116 also includes control circuits and timers for timing out the discrete time intervals of IMD operating states of a particular, typically programmed, mode of therapy delivery and/or monitoring. Typically, the delivery of a therapy, e.g., electrical stimulation or a drug, and the monitoring of a physiologic condition is cyclic, such that the control and timing circuit 116 times out active state intervals of therapy delivery and/or powering and monitoring the output of a physiologic sensor and times out relatively inactive or quiescent state intervals between such active state intervals. For example, an operating cycle may be marked by the successive delivery of an electrical stimulation therapy comprising a stimulation pulse with quiescent and sensing intervals timed out therebetween. In certain IMDs, the stimulation therapy comprises a train of N stimulation pulses, each pulse separated by a capacitor recharge interval. The control and timing circuit 116 is programmed in an operating mode to time out the active and quiescent state intervals, trigger the actions in the active states, and perform self-test or housekeeping functions in the quiescent state. The intervals of these operating states may be parameters that are programmable employing an external programmer 200. Parameters of the therapy delivery that affect the charge drawn from the battery 112 may also be programmable by the external programmer 200.

[0042] The timing and control functions of the MCU-based control and timing circuit 116 are governed in part by one or more system clocks. As disclosed in the above-referenced Biocontrol Medical patents, the MCU-based control and timing circuit 116 preferably comprises a low-speed CPU or processor and a high-speed CPU or processor or a combined low-speed and high-speed CPU or processor. The control and timing circuit 116 may comprise a microcomputer or microcontroller and/or discrete logic circuitry and analog circuit components that control the delivery of a therapy and/or monitor physiologic conditions of the patient during discrete time periods or intervals of an operating cycle.

[0043] The crystal 132 provides an accurate 32768 Hz slow clock that times the operation of the EMG processing circuit 104, the pressure sensor power and output signal processing circuit 108, and the low-speed processor to continuously monitor the EMG signal and apply power PS_P to the pressure sensor 142 and process the pressure output signal PS₀. The slow clock rate significantly reduces consumption of battery charge during the sensing state and any other quiescent or standby states. A high-speed, e.g., 2 MHz, clock may be developed by the MCU-based control and timing circuit 116 from an RC circuit.

[0044] When the low-speed processor detects a change in the EMG signal and/or the pressure output signal PSo during the time-out of a low current drain sensing state satisfying criteria signifying an imminent incontinence event, the fast clock is generated and applied to an A/D converter and the high-speed processor. The high-speed processor performs an accurate analysis of the EMG and pressure signals to determine whether stimulation is actually warranted. The high-speed processor is programmed to distinguish between signals indicative of possible incontinence and other signals that do not warrant stimulation to inhibit urine flow. In particular, the high-speed processor is preferably programmed to recognize signal patterns indicative of normal voiding, and does not trigger stimulation of the muscles when such patterns occur, so that the patient can pass urine normally.

[0045] The high-speed processor may analyze both long-term and short-term variations in the signals, as well as rates, spectral patterns, and patterns of change in the signals. For example, to inhibit stress incontinence, the highspeed processor may set a threshold of an aspect of the EMG signal that varies over time responsive to an assessment of the patient's physiological condition. Subsequently, a stimulation therapy is initiated only when a transient variation in the aspect of the EMG signal exceeds the threshold.

[0046] The IPG 100 may also be programmable to deliver a chronic stimulation regimen to counter urge incontinence. In such an urge incontinence mode, stimulation is delivered for the duration of an on-time and each successive stimulation therapy is separated by a quiescent off-time that is typically longer than the on-time. Thus, at least two current drain states are defined in such a chronic stimulation mode. [0047] A stimulation delivery state is entered when the applicable incontinence criteria are satisfied or optionally when the sensing state times out without being interrupted by satisfaction of the applicable incontinence criteria (which correlates to chronic stimulation for urge incontinence). In the stimulation current drain or operating state, the stimulation generating circuit 106 is operated by the MCU-based control and timing circuit 116 to generate and deliver a stimulation therapy regimen. Switches in the EMG processing circuit 104 are opened to isolate the IND and ACTIVE sensing /stimulation electrodes during delivery of a stimulation therapy regimen. Similarly, the pressure sensor power and output signal processing circuit 108 is instructed to halt applying power PSp to the pressure sensor 142 and processing the pressure output signal PSo for the duration of the stimulation state.

[0048] In one example disclosed in the above-referenced Biocontrol Medical patents, the entire sequence of signal detection and processing is estimated to take between 5 and 20 ms, up to the point at which the high-speed processor reaches a decision as to whether or not to trigger delivery of a stimulation therapy. The application of the stimulation therapy commences between 1 and 20 ms after the decision is reached, with the result that contraction of the pelvic muscles begins within 15-50 ms of an onset of increased EMG activity indicating impending urine loss. The stimulation pulse amplitude, width and number of delivered pulses, dictating the stimulation duration, may be programmable by the physician. Alternatively or additionally, stimulation is terminated if the patient voids voluntarily or other new data indicate that the expected incontinence is no longer likely. Stimulation is resumed if possible incontinence is again detected.

[0049] Thus, at least three operating states may be defined that recur periodically and exhibit differing current drain states. The sensing state and the therapy delivery state durations may vary, whereas the signal processing state may be relatively constant in duration. The rate of discharge of the battery 112 therefore depends on the current drain in each current drain or operating state and the durations of the states. The battery 112 may comprise a primary battery (non-rechargeable) and/or a rechargeable battery. Preferably, battery 112 comprises a standard primary IMD battery, such as a lithium-iodine battery, having a nominal output of 3.0 volts.

[0050] The battery 112 supplies voltage and current to all circuits and powered components of the IPG 100 and discharges over successive cycles as a function of the current drain imposed on the battery during the active and quiescent states. Generally speaking, during each cycle, the current drain during delivery of a therapy (in the therapy state) exceeds that drawn during sensing (in the sensing state), and the current drain during sensing exceeds that drawn in the quiescent interval(s) (in the quiescent state(s)). The relatively high therapy state current drain during electrical stimulation is associated with the charging or recharging of the output capacitor that is discharged through electrodes of an electrical medical lead to stimulate body tissue.

[0051] In accordance with one embodiment of the present invention, the MCU- based control and timing circuit 116 includes the state controller for changing the N operating states as described above and a state time timer ST-TIMER that times out the operating states. The MCU-based control and timing circuit 116 further comprises registers for storing the cumulative state times ST- TIME₁ - ST-TIME_N.

[0052] In one approach, the cumulative state times ST-TIME₁ - ST-TIMEN can be uplink telemetry transmitted via telemetry I/O transceiver 118 to an external medical device 200 of any of the types described herein for calculation of charges Q₁ - Q_N drawn in each operating state and the total charge Q drawn from the battery. To enable the calculation of Qi - Q_N, the current drain in each operating state (ST-CTDRN₁ - ST_CTDRN_N) is determined or estimated. The charges Q₁ - Q_N drawn in each operating state and the total charge Q drawn from the battery may then be estimated from the cumulative state times ST-TIMEi - ST-TIME_N and the current drains ST- CTDRN₁ - ST-CTDRN_N. An ERT may be optionally estimated from the average discharge rate, the total charge Q and the known capacity and discharge characteristics of the battery. The estimates of charge state and optionally the ERT may be calculated in the external medical device 200, displayed for the physician, and stored in patient records.

[0053] The MCU-based control and timing circuit 116 optionally comprises a calculator for calculating the cumulative charges Qi - QN drawn in each operating state and optionally the total charge Q and ERT, and registers for storing Qi - Q_N and/or Q and ERT between power-up of the IMD circuitry by the battery 112 to battery EOL. The estimates of the charges Q₁ - Q_N drawn in each operating state and/or the total charge Q and optionally the ERT may be calculated periodically and maintained in memory within the control and timing circuit 116 for uplink telemetry transmission via telemetry I/O transceiver 118 to an external medical device 200, e.g., a programmer. Optionally, the patient may be provided with an external medical device that periodically communicates with the IPG 100 to retrieve the estimates of the charge state and optionally the ERT and forward them over the internet, for example to a remote monitoring center in any of the ways known in the art.

[0054] The flowchart of FIG. 2 summarizes the above-described operations including the calculation and storage of the total charge Q or charge state by the timing and control circuitry 116 and the uplink telemetry transmission of the data to an external medical device 200. The charge calculation steps S114 — S116 may alternatively be performed by an external medical device receiving the uplink telemetry transmitted cumulative state times ST-TIME₁ - ST-TIME_N as described above.

[0055] Steps S 100 - S 102 set forth the initialization that takes place upon power-up. Steps S104 - S112 illustrate the accumulation of the cumulative • state times ST-TIMEi — ST-TIMEN during the subsequent operating states between power-up and battery EOL. At any time, the external medical device 200 may issue a UT DATA command (step S118) prompting the uplink telemetry transmission in step S120 of the computed value of total charge Q or charge state and/or ERT (step S116) and/or the cumulative value of the charges Qi - Q_N (step S114) and/or the cumulative state times ST-TIME₁ - ST-TIME_N depending on the UT DATA command and the capabilities of the IPG 100. Step S118 may occur during step S 106, and step S 120 may be delayed to take place following step S110. Step S118 is performed during the next operating state and does not necessarily interrupt or delay operation in the next state per steps S104 - S110.

[0056] All patents and publications referenced herein are hereby incorporated by reference in their entireties.

[0057] It will be understood that certain of the above-described structures, functions and operations of the above-described preferred embodiments are not necessary to practice the present invention and are included in the description simply for completeness of an exemplary embodiment or embodiments. It will also be understood that there may be other structures, functions and operations ancillary to the typical surgical procedures that are not disclosed and are not necessary to the practice of the present invention.

[0058] In addition, it will be understood that specifically described structures, functions and operations set forth in the above-referenced patents can be practiced in conjunction with the present invention, but they are not essential to its practice.

[0059] It is therefore to be understood, that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described without actually departing from the spirit and scope of the present invention.

Claims

1. A system of monitoring the amount of charge consumed from a battery powering a device operable in at least first and second current drain states comprising: means for selectively operating the device in one of a plurality of current drain states; means operable in each current drain state for timing the duration of the current drain state as a state time; means operable at each current drain state change for adding the state time to a cumulative state time for the current drain state; and means for calculating a charge drawn from the battery in each current drain state as a function of the current drain and the cumulative state time for the current drain state, whereby the amount of charge drawn from the battery is represented by the cumulative charges drawn in the current drain states.

2. The system of Claim 1 , further comprising: means for calculating the total charge drawn from the battery as a function of the cumulative charges drawn in all of the current drain states.

3. The system of Claim 2, wherein the device is an implantable medical device adapted to be implanted in a patient and the system further comprises: an external medical device having a telemetry transceiver adapted to transmit a command to initiate an uplink telemetry transmission from the implantable medical device; and wherein the implantable medical device comprises a telemetry transceiver adapted to receive a command from the telemetry transceiver of the external medical device and to uplink telemetry transmit one or more of the cumulative state times for the current drain states, the charges drawn from the battery in the current drain states, and the calculated total charge to the external medical device.

4. The system of Claim 1 , further comprising: means for calculating an elective replacement time of the battery as a function of the total charge and the battery capacity and discharge characteristics.

5. The system of Claim 4, wherein the device is an implantable medical device adapted to be implanted in a patient and the system further comprises: an external medical device having a telemetry transceiver adapted to transmit a command to initiate an uplink telemetry transmission from the implantable medical device; and wherein the implantable medical device comprises a telemetry transceiver adapted to receive a command from the telemetry transceiver of the external medical device and to uplink telemetry transmit one or more of the cumulative state times for the current drain states, the charges drawn from the battery in the current drain states, the calculated total charge drawn from the battery, and the elective replacement time to the external medical device.

6. The system of Claim 1. wherein the device is an implantable medical device adapted to be implanted in a patient and the system further comprises: an external medical device having a telemetry transceiver adapted to transmit a command to initiate an uplink telemetry transmission from the implantable medical device; and wherein the implantable medical device comprises a telemetry transceiver adapted to receive a command from the telemetry transceiver of the external medical device and to uplink telemetry transmit one or more of the cumulative state times for the current drain states and the charges drawn from the battery in the current drain states to the external medical device.

7. A system of monitoring the amount of charge consumed from a battery powering an implantable medical device adapted to be implanted in a patient and operable in at least first and second current drain states, wherein: the implantable medical device comprises: means for selectively operating the device in one of a plurality of current drain states; means operable in each current drain state for timing the duration of the current drain state as a state time; means operable at each current drain state change for adding the state time to a cumulative state time for the current drain state; and a first telemetry transceiver adapted to receive downlink telemetry transmissions and to uplink telemeter data, and the system further comprising an external medical device comprising a second telemetry transceiver adapted to downlink telemetry transmit a command to initiate an uplink telemetry transmission by the first telemetry transceiver of the cumulative state times for the current drain states.

8. The system of Claim 7, wherein the external medical device further comprises: means for calculating a charge drawn from the battery in each current drain state as a function of the current drain and the cumulative state time for the current drain state, whereby the amount of charge consumed from the battery is represented by the charges drawn from the battery in all of the current drain states.

9. The system of Claim 8, wherein the external medical device further comprises: means for calculating the total charge drawn from the battery as a function of the charges drawn from the battery in all of the current drain states.

10. The system of Claim 9, wherein the external medical device further comprises: means for calculating an elective replacement time of the battery as a function of the total charge and the battery capacity and discharge characteristics.

11. The system of Claim 7, wherein: the implantable medical device further comprises means for calculating a charge drawn from the battery in each current drain state as a function of the current drain and the cumulative state time for the current drain state; and the second telemetry transceiver of the external medical device is adapted to downlink telemetry transmit a command to initiate an uplink telemetry transmission by the first telemetry transceiver of the charges drawn from the battery in each current drain state, whereby the amount of charge consumed from the battery is represented by the cumulative charges drawn in the current drain states.

12. The system of Claim 11 , wherein: the implantable medical device further comprises means for calculating a cumulative charge drawn from the battery from the charges drawn in the current drain states; and the second telemetry transceiver of the external medical device is adapted to downlink telemetry transmit a command to initiate an uplink telemetry transmission by the first telemetry transceiver of the cumulative charge drawn from the battery in the current drain states.

13. The system of Claim 12, wherein: the implantable medical device further comprises means for calculating an elective replacement time of the battery as a function of the total charge and the battery capacity and discharge characteristics; and the second telemetry transceiver of the external medical device is adapted to downlink telemetry transmit a command to initiate an uplink telemetry transmission by the first telemetry transceiver of the elective replacement time.

14. A method of monitoring the amount of charge consumed from a battery powering a device operable in at least first and second current drain states comprising: selectively operating the device in one of a plurality of current drain states; in each current drain state, timing the duration of the current drain state as a state time; adding the state time to a cumulative state time for the current drain state; and calculating a charge drawn from the battery in each current drain state as a function of the current drain and the cumulative state time for the current drain state, whereby the amount of charge consumed from the battery is represented by the cumulative charges drawn in the current drain states.

15. The method of Claim 14, wherein the device is an implantable medical device adapted to be implanted in a patient having a telemetry transceiver, and the method further comprises: providing an external medical device having a telemetry transceiver; transmitting a command to initiate an uplink telemetry transmission from the implantable medical device to the external medical device; receiving the transmitted command by the telemetry transceiver of the implantable medical device; and uplink telemetry transmitting one or more of the cumulative state times for the current drain states and the charges drawn from the battery in the current drain states.

16. The method of Claim 14, further comprising: calculating the total charge drawn from the battery as a function of the cumulative charges drawn in all of the current drain states.

17. The method of Claim 16, wherein the device is an implantable medical device adapted to be implanted in a patient having a telemetry transceiver, and the method further comprises: providing an external medical device having a telemetry transceiver; transmitting a command to initiate an uplink telemetry transmission from the implantable medical device to the external medical device; receiving the transmitted command by the telemetry transceiver of the implantable medical device; and uplink telemetry transmitting one or more of the cumulative state times for the current drain states, the charges drawn from the battery in the current drain states and the calculated charge state of the battery to the external medical device.

18. The method of Claim 16, further comprising: calculating an elective replacement time of the battery as a function of the total charge and the battery capacity and discharge characteristics.

19. The method of Claim 18, wherein the device is an implantable medical device adapted to be implanted in a patient having a telemetry transceiver, and the method further comprises: providing an external medical device having a telemetry transceiver; transmitting a command to initiate an uplink telemetry transmission from the implantable medical device to the external medical device; receiving the transmitted command by the telemetry transceiver of the implantable medical device; and uplink telemetry transmitting one or more of the cumulative state times for the current drain states, the charges drawn from the battery in the current drain states, the calculated charge state of the battery, and the elective replacement time to the external medical device.

20. In a system comprising an implantable medical device adapted to be implanted in a patient and operable in at least first and second current drain states and an external medical device, a method of monitoring the amount of charge consumed from a battery powering the implantable medical device, wherein: the operation of the implantable medical device comprises: selectively operating the device in one of a plurality of current drain states; in each current drain state, timing the duration of the current drain state as a state time; adding the state time to a cumulative state time for the current drain state; and transmitting the cumulative state times of the current drain states in response to a command from the external medical device, and the operation of the external medical device comprises: transmitting a command to the implantable medical device; and receiving the cumulative state times for the current drain states transmitted by the implantable medical device.

21. The method of Claim 20, wherein the operation of the external medical device further comprises: calculating a charge drawn from the battery in each current drain state as a function of the current drain and the cumulative state time for the current drain state, whereby the amount of charge consumed from the battery is represented by the charges drawn from the battery in all of the current drain states.

22. The method of Claim 21 , wherein the operation of the external medical device further comprises calculating the total charge drawn from the battery as a function of the charges drawn from the battery in all of the current drain states.

23. The method of Claim 22, wherein the operation of the external medical device further comprises calculating an elective replacement time of the battery as a function of the total charge and the battery capacity and discharge characteristics.

24. The method of Claim 20, wherein: the operation of the implantable medical device further comprises: calculating a charge drawn from the battery in each current drain state as a function of the current drain and the cumulative state time for the current drain state; and transmitting the charges drawn in the current drain states in response to a command from the external medical device, and the operation of the external medical device comprises: transmitting a command to the implantable medical device; and receiving the charges drawn in the current drain states transmitted by the implantable medical device.

25. The method of Claim 24, wherein: the operation of the implantable medical device further comprises: calculating the total charge drawn from the battery from the charges drawn in the current drain states; and transmitting the total charge drawn from the battery in response to a command from the external medical device, and the operation of the external medical device comprises: transmitting a command to the implantable medical device; and receiving the total charge drawn from the battery transmitted by the implantable medical device.

26. The method of Claim 25, wherein: the operation of the implantable medical device further comprises: calculating an elective replacement time of the battery as a function of the total charge drawn from the battery and the battery capacity and discharge characteristics; and transmitting the cumulative charges drawn from the battery in response to a command from the external medical device, and the operation of the external medical device comprises: transmitting a command to the implantable medical device; and receiving the elective replacement time of the battery transmitted by the implantable medical device.