Active implantable medical device and method for determining available capacity of its battery

Abstract

The present invention relates to a method for determining the available capacity of a battery of an active implantable medical device, in particular a cardiac stimulator, the active implantable medical device comprising a radio frequency (RF) communication unit for transmitting data during an RF communication period and wherein the battery of the active implantable medical device can be used to transmit data by RF via the RF communication unit, the method comprising: a) a step for measuring a value of a battery voltage VBi representing an instantaneous voltage drop dVBi of the battery of said device due to a current load on the battery, b) a step for comparing said voltage VBi of the battery with a predetermined threshold voltage VBS, and c) a step for transmitting an alarm message to another device when said measured voltage VBi of the battery crosses the predetermined threshold voltage VBS. The invention also relates to an active implantable medical device performing the method.

Description

Technical Field

[0001] The invention relates to an active implantable medical device, in particular a cardiac stimulator or a neurostimulator, equipped with a radio frequency (RF) link, in particular for communicating with another device, in particular another external non-implantable device, and a method for determining the available capacity of its battery. Background Art

[0002] An active implantable device may include a radio frequency (RF) communication unit for enabling communication with another device, particularly an external device such as a programmer used by a practitioner, a home monitor, a smartphone, or any other device. Here, the term "communication" should be understood to mean any communication between an implantable device and another device, regardless of whether there is a response from the other device.

[0003] For patients wearing active implantable medical devices with RF communication components, it is crucial to be able to determine the available capacity of the battery of this type of device. Except in the case of implantable defibrillators, the battery of the implantable medical device is exposed to much higher currents during the radio frequency communication process than when the treatment is given. Therefore, it is necessary to define indicators that will trigger an alarm that notifies medical personnel that the RF link can no longer be used. In fact, it is necessary to inform the practitioner of the failure of the RF communication component so that the practitioner can then replace the device in order to continue to monitor the patient remotely.

[0004] It has been observed that the battery data provided by its manufacturers do not correspond to the actual conditions of RF use. For this reason, as it currently stands, these data cannot be used to determine whether the capacity of the battery is sufficient for RF. In fact, conventionally, the information provided relates to the open circuit voltage (or low load voltage or static voltage) and the voltage when the battery is subjected to a large current (e.g. 5 mA to 30 mA), which is stable over a predefined period of time. These data can be used alone or in combination, but they cannot be applied to the dynamic current distribution during RF communication, which is characterized by large fluctuations in current associated with the communication protocol. Compliance with these data will then lead to a considerable margin built in, which will seriously affect the available capacity, or actually lead to an overestimation of the available capacity, thereby risking damage to active implantable medical devices when RF is used beyond a certain level of depletion.

[0005] Another known method consists in continuously measuring the voltage or impedance of the battery during the communication by RF, for example in a way to check whether the battery has reached a predetermined threshold. The load on the battery occurs essentially during remote monitoring or in the presence of a practitioner. It is therefore not enough to wait for the patient to have the next check by RF communication to know whether the battery status is still able to use the RF link. In fact, there may be several months or even a year between two checks. This may lead to the fact that when the check has taken place, the performance of the active implantable medical device may be degraded and therefore the battery is no longer able to support the load, or indeed the RF link may be interrupted once the threshold is reached.

[0006] When the usage limits of the RF link coincide with the recommended replacement time (RRT), it is necessary to precisely define the remaining lifetime every time an active implantable medical device is interrogated. Such remaining lifetime indicators rely on the evaluation of the battery's exhaustion level. Therefore, it is necessary to have reliable and available indicators and update them very regularly, such as daily or weekly, while assuring doctors and patients of the optimal lifetime of the RF. Summary of the invention

[0007] The object of the invention is to define a method that optimizes the determination of the available capacity of a battery that can be used for communicating with a programmer, a home monitor or any other device, especially an external device, via an RF link.

[0008] The object of the present invention is achieved by means of a method for determining the available capacity of a battery of an active implantable medical device, in particular a cardiac stimulator, the active implantable medical device comprising a radio frequency (RF) communication unit for transmitting data by RF during a communication period, and wherein the available capacity of the battery of the active implantable medical device enables transmission of data by RF via the RF communication unit, the method comprising: a) a step for measuring a value of a battery voltage VBi representing an instantaneous voltage drop dVBi of the battery of said device due to a current load on the battery, b) a step for comparing said voltage VBi of the battery with a predetermined threshold voltage VBS, and c) a step for transmitting an alarm message to another device when said measured voltage VBi of the battery crosses the predetermined threshold voltage VBS.

[0009] The invention exploits the fact that the transient drop in voltage at the start of loading provides sufficient information to determine the capacity of the battery. The method can therefore be used to increase the service life of active implantable medical device batteries, in particular by eliminating the considerable margin derived from the manufacturer's data, which would seriously reduce the available capacity. The observed transient drop is particularly related to the resistive part of the battery.

[0010] The invention relating to a method for determining the available capacity of a battery of an active implantable medical device can be further improved by means of the following embodiments.

[0011] According to one embodiment, the load may correspond to a current consumption for a period of less than 20 ms, in particular less than 10 ms.

[0012] Thus, by applying a pulse of a shorter duration than the communication duration necessary for data transmission, it is possible to determine the available capacity of the battery. For this purpose, it is not necessary to use a full data transmission via RF to determine the available capacity, i.e. RF communication is used during a remote examination or during an examination with the practitioner present (which only occurs once a year).

[0013] According to one embodiment, step a) may comprise measuring at least one high peak voltage and a next low peak voltage of the battery voltage oscillating between peak-to-peak during RF communication.

[0014] Thus, any type of RF communication of the implanted device may be used, such as during "advertising" according to the Bluetooth protocol or during periodic exchanges between the device and any external device, to determine the state of the battery. The determination of high and low values ​​can be made at any time, since the instantaneous drop between a high value and the next low value is primarily related to the resistive portion of the battery, which is substantially constant for a given battery depletion state.

[0015] According to one embodiment, step a) may further comprise measuring the open circuit voltage of the battery before any loading.

[0016] Thus, even if high and low peak voltages are measured during transmission, the measurement of the open circuit voltage may be used to normalize the measurement so that a comparison with a predetermined threshold voltage VBS can be performed.

[0017] According to one embodiment, the current consumption may be at least 100 times shorter, in particular at least 1000 times shorter than the predetermined duration of the data transmission.

[0018] Therefore, the battery only needs to be loaded slightly to determine the battery's usable capacity.

[0019] According to one embodiment, the current consumption can be generated using a peak current, which corresponds to the maximum current present during RF data transmission. Thus, the obtained situation is comparable to data transmission, which makes the method for determining whether the battery can still transmit data via RF more reliable.

[0020] According to one embodiment, the step of measuring the voltage VBi of the battery of the active implantable medical device may be performed periodically, in particular daily.

[0021] Thus, the voltage VBi of the battery can be measured more regularly and the life prediction can be evaluated and will be available for each interrogation, whether it is performed remotely or in a hospital environment. In addition, since the current consumption is of short duration, the impact on the battery life is negligible. In fact, it is obviously not a problem to measure the battery voltage regularly, the battery voltage is subjected to a duration equal to the current consumption through the RF data transmission. Therefore, the life of the device is not impaired in any substantial way.

[0022] According to one embodiment, the predetermined threshold voltage VBS may represent a threshold voltage which still allows at least one data transmission via RF from the active implantable medical device to another device, in particular another non-implantable external device.

[0023] Thus, at least one alarm message can still be transmitted to another device, in particular an external non-implanted device.It is then possible to warn medical personnel of this depleted state of the battery.

[0024] According to one embodiment, the predetermined threshold voltage VBS may be higher than a limit voltage VBref representing an operating limit of the RF communication circuit of the active implantable medical device.

[0025] The method thus provides a safety margin, thereby ensuring that at least the alarm message is transmitted before the RF link can no longer be used.

[0026] According to one embodiment, the current consumption may be generated using an RF unit of the active implantable medical device.

[0027] Thus, the present invention can be implemented without a dedicated supplemental source of current required for current consumption.

[0028] According to one embodiment, the generation of the current consumption may include the generation of a carrier wave with or without the activation of at least a portion of the functionality necessary for the RF data transmission.

[0029] Thus, current can be provided via the RF unit by activating the element generating the peak current required during RF data transmission.Thus, the method can be used to generate a current comparable to the current during RF data transmission.

[0030] According to one embodiment, the generation of the current consumption comprises using a connection scanning channel in order to initiate RF communication of the active implantable medical device with another device, in particular using a main advertising channel of the Bluetooth protocol.

[0031] Therefore, if the current represents the peak current during RF communication, the current draw can be one of the currents already present in the connection scan protocol. This also ensures that there is no communication interruption in the environment of the wearer of the active implantable medical device.

[0032] According to a variant, the method may comprise a step for determining the remaining capacity and / or remaining life of the battery as a function of the measured voltage VBi. This can be done by comparing the voltage VBi with a table stored in a memory of the active medical device. To determine the remaining life, past use of the battery may be taken into account.

[0033] According to one embodiment, the method may include the transmission of a message as a function of the remaining capacity and / or remaining life of the battery. Thus, a message is transmitted, which means that the user or processing personnel can know how long the time of data transmission via RF will likely be.

[0034] According to one embodiment, the method may comprise a step for transmitting the value Vbi to another device upon request of the other device and / or the user.

[0035] Thus, the remaining capacity and / or the remaining lifetime can also be established outside the active medical device. This reduces the need for memory and computing power in the active implantable medical device, thereby enabling a reduction in the energy consumption and volume of the device.

[0036] According to one embodiment, the method may comprise a step for authorizing or not authorizing automatic monitoring as a function of VBi.

[0037] Depending on the health of the user, the practitioner can program the implantable medical device in a way such as authorizing the transmission of data by RF or other means. For patients who do not need transmission, the component is not used, which means that the service life of the battery can be extended. However, after the health of the user degrades, the practitioner can decide that automatic transmission of data by RF should be used. If the value of VBi is already below the threshold VBS at this time, the use of the RF component will be blocked in order to prevent malfunction of the device.

[0038] According to one embodiment, after a predetermined threshold voltage VBS is crossed, RF data transmission from the active medical device may be suspended.

[0039] Thus, the active medical device may still be used without the component until another parameter is reached, such as a recommended replacement time.

[0040] The object of the present invention is also achieved by an active implantable medical device equipped with an RF link, the active implantable medical device comprising a battery, an RF unit and a controller. The controller is configured to execute the method as described above.

[0041] Thus, it is possible to determine the available capacity of the battery by applying a pulse of a shorter duration than the communication duration required for the RF data transmission. Thus, it is not necessarily necessary to invoke a complete transmission of RF data (i.e., using RF communication during remote monitoring or when monitoring is performed in the presence of a practitioner, which communication can additionally only be performed once a year) in order to determine the available capacity. In other words, with the active implantable medical device of the present invention, it is possible to determine whether data transmission is still possible without establishing RF communication. Furthermore, since the duration of the current consumption is shorter than the RF data transmission, the impact on the battery life is negligible. Thus, it is possible to increase the battery life of the active implantable medical device, in particular by eliminating the considerable margin derived from the manufacturer's data, which seriously affects the available capacity. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] The present invention and its advantages will be described in more detail below through preferred embodiments, especially with reference to the accompanying drawings, in which:

[0043] [ Figure 1 ] represents an organizational structure diagram of a method for determining the available capacity of a battery of an active implantable medical device according to the present invention;

[0044] [ Figure 2 ] represents an active implantable medical device according to the present invention;

[0045] [ Figure 3 ] illustrates a graph representing voltage in a battery subject to current drain during RF data transmission;

[0046] [ Figure 4 ] illustrates a graph representing battery voltage as a function of average current when the battery is subjected to current drain for a duration representative of RF data transmission;

[0047] [ Figure 5 ] illustrates a graph of battery voltage as a function of average current when the battery is subjected to current drain over a duration representative of RF data transmission, and determination of dVBi when no measurement is made at the beginning of RF data transmission; DETAILED DESCRIPTION

[0048] In order to ensure that the battery of an active implantable medical device with radio frequency communication means RF is still able to provide the power required to transmit RF data, the present invention proposes a method that can be used to check the status of the battery regularly (for example daily) without loading the battery itself too much. The conditions for RF transmission are usually predetermined, and the transmission speed, the size of the memory pool to be transferred and the duration of the communication are known. There are various types of RF communication, such as, for example, periodic wake-ups with short communications lasting from a few milliseconds to tens of milliseconds in order to check whether communication is necessary (for example by using the "advertising" mode of the Bluetooth standard). Communication via RF can also be used to send messages to indicate whether to communicate with another device. It can be a communication with a data transmission lasting less than 1 second. Finally, it can be a communication with a data transmission that may last for tens of seconds. With the help of Figure 1 An organizational diagram is used to describe a method for determining available capacity of a battery of an active implantable medical device according to one embodiment of the present invention.

[0049] During a first step 12 of the method 10 according to the invention, a defined current consumption having a duration Δtpulse and a strength representative of a peak current required for data transmission by an active implantable medical device via RF is triggered. The current consumption has a duration Δtpulse of less than 20 ms, in particular less than 10 ms, which is therefore short enough to substantially correspond to a momentary drop in the battery voltage.

[0050] Thus, the duration of current consumption is shorter than the duration of RF data transmission. For a typical transmission of RF data of a stimulator, this duration is shortened by at least a factor of 100, more specifically, by at least a factor of 1000.

[0051] During a second step 14 of the method 10 according to the invention, the VBi of the battery (also denoted as VB in the figures) is measured at the end of the current consumption triggered in step 12. i ). This voltage represents the instantaneous drop in the battery after the battery is loaded.

[0052] During a third step 16 of the method 10 according to the invention, the measured voltage VBi is compared to a predetermined threshold voltage VBS of the battery (also indicated as VB in the figures). S ) for comparison.

[0053] If the voltage VBi measured at the end of the current consumption is greater than a predetermined threshold voltage VBS of the battery, this means that the battery of the active implantable medical device still has available capacity for ensuring data transmission via RF. Once this threshold is crossed, data transmission via RF can no longer be guaranteed. As indicated by arrow 18, method 10 then returns to step 12. Step 12 can be repeated at close intervals, for example once a day.

[0054] It should be noted that the predetermined threshold voltage VBS of the battery is fixed throughout the service life of the battery. Therefore, it is not necessary to re-determine the value of the predetermined threshold voltage VBS of the battery.

[0055] In the event that the voltage VBi measured at the end of the current consumption is less than or equal to the predetermined threshold voltage VBS of the battery, an alarm message is transmitted during step 20 to warn the medical staff or user that the battery has reached the predetermined threshold voltage VBS of the battery, which may or may not require replacement of the implanted medical device, depending on whether the threshold VBS is the same as the recommended replacement time. According to a variant, the voltage VBi can serve as a reference in order to determine the remaining capacity of the battery for RF use and therefore as a basis for determining the remaining life of RF use before the voltage VBS is reached.

[0056] Considering that the voltage VBi is measured periodically, for example daily, this remaining lifetime is available and up to date each time the active implantable medical device is interrogated, whether this is done remotely or in the presence of a practitioner. Thus, the value VBi can be sent to another device which can determine the remaining capacity and / or the remaining lifetime from a table or an algorithm. According to a variant, the remaining capacity or the remaining lifetime can also be determined in the active medical device.

[0057] It should be noted that voltage VBi can serve as a reference for the remaining lifetime indicator of an active implantable medical device if cessation of RF use coincides with the recommended replacement time.

[0058] If the cessation of RF use does not coincide with the recommended replacement time, crossing the threshold will cause the RF component to cease operation. However, the active medical device can still be used until the recommended replacement time. If the user's health status allows, the device can still be used, thereby delaying the time when the device must be replaced.

[0059] According to another way of using voltage VBi, reaching voltage VBS can also be used to program the device without authorizing future remote monitoring that was not previously possible.

[0060] Since it is not necessary to periodically measure the voltage of the battery, which is subjected to a current draw equal to the duration of the RF data transmission, the determination of the available capacity has less impact on the battery life. In fact, since the duration of the current draw is short compared to the duration of the RF data transmission, the impact of this type of current draw on the battery life is negligible. In addition, the method 10 can be used to perform periodic measurements, such as daily, and can be used to perform non-urgent replacement of active implantable medical devices when necessary.

[0061] The present invention also relates to an active implantable medical device equipped with an RF link, the active implantable medical device comprising a battery, an RF unit and a controller. The controller is configured to Figure 1 The method 10 is described to determine the available capacity.

[0062] Figure 2 An active implantable medical device 20 of this type configured according to the invention is illustrated. The active implantable medical device 20 is configured so as to be able to generate a wireless link of the radio frequency RF type with another device, in particular with another external device 22. The implantable medical device 20 may be a cardiac stimulator or a neurostimulator. The other device, in particular the other external device 22, may be a programmer used by a clinical practitioner, a home monitor or any other device. The active implantable medical device 20 comprises a radio frequency unit (RF) 24 capable of communicating with another device, in particular with another external device 22. It comprises a battery 26 for allowing RF communication. The battery 26 also provides the energy required for administering the therapy generated by a controller 28 that manages one or more electrodes 29. In addition, the active implantable medical device 20 comprises a controller 30, which is configured to determine the state of the battery 26 according to the method 10 described below. Therefore, the state of the battery 26 is determined by means of a short current consumption for a duration Δtpulse less than 20ms, in particular less than 10ms, so that it is shorter than the duration during which RF data is usually transmitted from the device 20 and is used to transmit data to other devices, in particular to other external devices 22.

[0063] According to an embodiment, the current consumption can be achieved using the RF unit of the active implantable medical device. In this case, the current is provided via the RF unit by activating an element that generates the peak current required during RF data transmission. The interest is in generating the same current without having to call for a supplementary current source. The peak current is obtained by generating a carrier and activating other functions, thereby requiring a significant current during radio frequency data transmission.

[0064] According to another variant, the controller 30 is configured to use a communication protocol, in particular a connection scanning protocol, to generate the current consumption. Thus, the method 10 can be performed with components already available in the active implantable medical device 20.

[0065] Figure 3 Illustrated is a graph representing battery voltage subject to current consumption as a function of time and representing the start of RF data transmission.

[0066] When the battery is subjected to the dynamic current drain regime of radio frequency data transmission, for example by using the Bluetooth protocol or any other suitable RF communication protocol, the battery's behavior causes a transient voltage drop at each current drain, which is obviously to a greater or lesser extent a function of the filtering capacity usually connected to the battery. This transient drop is mainly related to the resistive part of the battery, which can be considered as a constant at a given battery depletion state.

[0067] like Figure 3 As seen in FIG. 1 , during RF data transmission, the battery voltage VB oscillates between a high peak voltage VBi high and a subsequent low peak voltage VBi low.

[0068] A gradual drop will also be observed with RF communication or RF data transmission. Thus, the voltage curve of the battery is associated with a higher current (also called peak current that produces these instantaneous voltage drops) and an average current provided to produce RF data transmission, which is the basis for the gradual voltage drop.

[0069] Figure 3 The instantaneous relative voltage drop denoted dVBi in the diagram (also denoted dVBi in the figure) occurs at each current consumption of the RF data transmission. Thus, when the battery is loaded at time t=0, the instantaneous drop dVBi is the same as a little later, for example at 0.4 s or 1.65 s. The battery voltage reached at the end of the RF data transmission depends on the instantaneous current responsible for the instantaneous drop and the average current responsible for its gradual drop. Thus, two parameters can be defined: the first parameter (at t=0) Figure 3 ) is the battery voltage at the end of a single current consumption, which is short and represents the instantaneous voltage drop dVBi during the peak current; and the second parameter is the voltage at the end of a single current consumption with a predefined duration, which is equal to RF data transmission and the current is equal to the peak current, which will be related to Figure 4 and Figure 5 Explain in more detail.

[0070] Here, for the first parameter, the term "short duration current consumption" is understood to mean a duration at least equal to the duration of the current consumption responsible for the momentary drop in battery voltage, i.e. of the order of 1 ms, and at most not exceeding 20 ms. Beyond this, the voltage drop becomes increasingly higher and less representative.

[0071] Typical values ​​for maximum peak current during RF data transmission for active implantable medical devices (such as, cardiac stimulators) are on the order of 5mA to 30mA; the average current is on the order of 2mA to 10mA, and the duration of RF communication for complete transmission of data in the implant's memory is on the order of 10s to 60s.

[0072] Figure 4 A graph showing the battery voltage at the end of an RF data transmission of a predefined duration as a function of the average current intensity drawn from the battery during the RF data transmission along the abscissa and the battery depletion as a function of the ordinate. The first order approximation of the relationship between the voltage at the end of the RF data transmission and the average current is a linear relationship. Figure 4 In FIG. 1 , the voltage VBi, i=1 to n, corresponds to the battery voltage after the instantaneous voltage drop after the battery is loaded.

[0073] For a short current consumption, the current relative to the duration of the RF data transmission is negligible and the instantaneous voltage drop can therefore be placed at the origin of the abscissa. VBi then corresponds to the voltage observed at the end of a short current consumption of defined duration Δtpulse.

[0074] Conversely, the higher the average current, the closer it is to the peak current. By linear approximation, the straight line is extended to the point corresponding to the peak current (IBpeak). Therefore, this point corresponds to the current consumption of the duration of RF data transmission, where the current is constant and equal to the peak current.

[0075] Figure 4 The points Ai, i=1 to n, with coordinates (Ibpeak; VBipeak) in the diagram of correspond to a current consumption for a duration equal to the duration of the RF data transmission, the average transmission current of which is equal to the peak current IBpeak, i.e. the maximum instantaneous current provided by the battery for the RF data transmission during the entire predetermined duration. Depending on the parameterization of the RF communication of the device, the average current is therefore between two extreme values ​​I=0 and I=IBpeak. To a first order approximation, the voltage of the battery will be on the straight line connecting these two extreme points Ai and (0, VBi).

[0076] Depending on the depletion of the battery, the plot VBi(Imean) is gradually displaced downwards, as indicated by the arrow and by the second straight line defined by the point Ai and (0, VBi). It will be observed that the voltage drop VBipeak increases as a function of depletion with a decrease in the voltage VBi. This necessarily means that from a certain degree of depletion, the limiting voltage of the battery will be reached, for which the RF data transmission operation will no longer be guaranteed. The object of the invention is therefore to predict a good and reliable operation of an active implantable medical device and to optimize the available capacity of the battery.

[0077] The invention is based on the fact that battery manufacturers are able to provide the variation of the battery voltage for a given peak current, as well as the duration corresponding to a short current drain and the determined duration corresponding to a data transmission, and thus the values ​​VBi and Ai. With the aid of these manufacturer's data, it is obtained Figure 4It is possible to define the depletion level of the battery as a function of the straight line VBi(Imean) as illustrated in FIG. 1 . In addition, it is possible to define the depletion level of the battery as a function of the straight line VBi(Imean) as illustrated in FIG. 1 , where the straight line defined by AS and VBS (also indicated as A in the figure) s ) through point BS (also indicated as B in the attached figure) s ), this point BS corresponds to the limit voltage (VBref) and average current (IBref) that ensure RF data transmission operation.

[0078] The average current IBref for the transmission of RF type data from the stimulator can be determined experimentally. In addition, the design of a given implantable medical device also means that a limit voltage VBref necessary for correct operation and in particular necessary to ensure the RF link can be defined. This voltage can also be determined experimentally. These values ​​then determine the point BS, such as Figure 4 Explained in .

[0079] Assuming a linear dependence between voltage and average current, extrapolating a straight line VBS(Imean) through the points AS and BS towards the origin of the abscissa will provide a limit voltage VBS that will not be exceeded after a short current drain is applied. It is therefore now only necessary to compare the voltage VBi, which represents the battery voltage, measured at the end of a short current drain of short duration Δtpulse with the threshold value VBS of the battery's limit voltage to determine whether the available capacity of the battery is still sufficient. Since VBi can be determined with very short loads on the battery, tests can be performed regularly and frequently, for example every day.

[0080] Given the required energy, Vbipeak is measured periodically in order to take into account the point AS for each battery used in an active implantable medical device, in order to be able to determine a threshold voltage VBS that cannot be conceived; it is more advantageous to establish a common threshold for several batteries of the same type of active implantable medical device. Thus, it is not necessary to determine VBSpeak separately for each device.

[0081] For safety reasons, the voltage VBSpeak chosen to establish the straight line VBS(Imean) corresponds to the voltage VBpeak of a lower voltage with the same peak current IBpeak observed for a series of batteries of the same type. In other words, the VBSpeak taken into account as a reference voltage may correspond to the "worst case" battery in order to introduce a safety margin. This battery will have a passing point BS and will have the straight line VBS(Imean) with the greatest reduction.

[0082] The threshold voltage VBS of the battery, defined by the reference straight line VBS (Imean), serves as a reference point for the battery assembly. Due to the safety margin introduced by the reference straight line VBS (Imean), the threshold voltage VBS of the battery means that the limiting operating voltage Vbref of the battery cannot be reached when the threshold voltage VBS is reached during the measurement of the short current consumption. In fact, depending on the level of exhaustion of the battery, the battery voltage VBi measured at the end of the short current consumption will decrease from the value VB1 to VBS, which ensures that the battery voltage reached at the end of the RF data transmission remains above VBref. The successive straight lines connecting the point Ai and the point (0; VBi) will be displaced in the following way: descending towards the abscissa as a function of the battery exhaustion and approaching the reference straight line VBS (Imean). At the moment of reaching the threshold voltage VBS, it will be possible to perform one or more data transmissions from the active implantable medical device to another device, in particular to another external non-implantable device, by RF. This can preferably be an RF data transmission, which enables the transmission of all useful information and in particular enables the transmission of data present in the memory. According to an alternative, it may also be an alarm message in order to warn the medical staff of this exhaustion phase of the battery.

[0083] Therefore, the safety margin introduced by the reference straight line VBS(Imean) ensures that at least RF data or an alarm message is transmitted before the RF link can no longer be used. It should be noted that the voltage VBS serves as a reference for a predetermined threshold voltage for a plurality of active implantable medical devices. Therefore, it is not necessary to redefine VBS for each device.

[0084] Figure 5 Illustrated are graphs representing battery voltage as a function of average current when the battery is subjected to current drain over a duration representing RF data transmission, and graphs representing determination of dVBi when the measurement is neither made at the beginning of RF data transmission nor with a current load that varies with VBi measurement.

[0085] As already mentioned above, in RF data transmission, a momentary voltage drop is found at each current consumption. Figure 3 Thus, at the moment of loading the battery at t=0, the instantaneous drop dVBi is the same as later at 0.4 s or 1.65 s.

[0086] Therefore, according to the alternative scheme, as regards Figure 1 and Figure 2 The method described can also be performed in case of any momentary drop during RF data transmission. By measuring the battery voltage VB (which oscillates between high and low values ​​during RF data transmission) (e.g. Figure 3The value dVBi can also be determined by taking into account the high peak voltage "Vbi high" (at 0.4s in the figure) and the next low peak voltage "Vbi low". Conversely, the open circuit voltage value VBGi of the battery at the measurement moment must also be taken into account in order to obtain the value VBi. In fact, VBi = VBGi - (VBi high - Vbi low).

[0087] like Figure 3 As can be seen in FIG. 1 , the open circuit voltage VBG also decreases due to the battery depletion state.

[0088] In order to reduce the error margin, it is also possible to determine dVBi several times during RF data transmission, or to determine an envelope Eh through high values ​​and another envelope El through low values ​​and determine the distance between the two.

Claims

1. A method for determining the available capacity of a battery of an active implantable medical device, the active implantable medical device comprising an RF communication unit for transmitting data by RF during a communication period, and wherein the available capacity of the battery of the active implantable medical device enables the transmission of data by RF via the RF communication unit, the method comprising: a) the step of triggering a current load having a predetermined pulse duration and a magnitude representative of a peak current required for RF data transmission; b) a step for performing a measurement of the voltage VBi of said battery during a transient voltage drop dVBi due to said defined current load, c) a step of comparing said voltage VBi of said battery with a predetermined threshold voltage VBS, and d) a step for transmitting an alarm message to another device through RF when the voltage VBi of the battery becomes less than or equal to the predetermined threshold voltage VBS, wherein the alarm message indicates that the RF communication unit cannot be used any more.

2. The method according to claim 1, characterized in that The active implantable medical device is a cardiac stimulator.

3. The method according to claim 2, characterized in that The current load corresponds to a current consumption for a period of less than 20 ms.

4. The method according to claim 3, characterized in that The current load corresponds to a current consumption for a period of less than 10 ms.

5. The method according to claim 1 or claim 3, characterized in that: Step b) comprises the measurement of at least one high peak voltage and a next low peak voltage of the voltage of said battery oscillating between peak-to-peak during RF transmission.

6. The method according to claim 5, characterized in that Step b) further comprises measuring the open circuit voltage of the battery before any loading.

7. The method according to claim 3, characterized in that The current consumption is at least 100 times shorter than a predetermined duration of the data transmission.

8. The method according to claim 7, characterized in that The current consumption is at least 1000 times shorter than a predetermined duration of the data transmission.

9. The method according to claim 3, characterized in that The current consumption is generated with a peak current corresponding to the maximum current present during RF data transmission.

10. The method according to claim 3, characterized in that Steps a) to d) are performed periodically.

11. The method according to claim 10, characterized in that Steps a) to d) are performed daily.

12. The method according to claim 1, characterized in that The predetermined threshold voltage VBS represents a threshold voltage that still allows at least one RF transmission from the active implantable medical device to another device.

13. The method according to claim 2, characterized in that The predetermined threshold voltage VBS is higher than a limit voltage VBref representing an operating limit of the RF communication circuit of the active implantable medical device.

14. The method according to claim 3, characterized in that The current consumption is generated using an RF unit of the active implantable medical device.

15. The method according to claim 14, characterized in that The generation of the current consumption includes the generation of a carrier wave with or without the activation of at least a portion of the functions necessary for RF data transmission.

16. The method according to claim 14 or claim 15, characterized in that The generation of the current consumption includes using a connection scanning channel to initiate RF communication of the active implantable medical device with another device.

17. The method according to claim 16, characterized in that The generation of the current draw includes using a primary channel of the Bluetooth protocol to initiate RF communication of the active implantable medical device with another device.

18. The method of claim 1, wherein: A step is included for determining the remaining capacity and / or the remaining life of said battery as a function of the voltage VBi.

19. The method according to claim 18, characterized in that Further included is the transmission of a message as a function of the remaining capacity and / or remaining life of the battery.

20. The method of claim 1, wherein: Steps are included for transmitting the value VBi to another device upon request of the other device and / or the user.

21. The method of claim 1, wherein: Steps are included for automatic monitoring of authorization or non-authorization as a function of VBi.

22. The method of claim 1, wherein: After the predetermined threshold voltage VBS is crossed, RF data transmission from the active implantable medical device is suspended.

23. An active implantable medical device comprising an RF communication unit (24), a battery (26) and a controller (30); wherein the controller (30) is configured to perform: triggering a predetermined pulse duration and a defined current load representing the intensity of the peak current required by RF data transmission; measuring the voltage VBi of the battery during a transient voltage drop dVBi due to the defined current load, comparing the voltage VBi of the battery with a predetermined threshold voltage VBS, and transmitting an alarm message to another device via RF when the voltage VBi of the battery becomes less than or equal to the predetermined threshold voltage VBS; The alarm message indicates that the RF communication unit can no longer be used.

24. The active implantable medical device of claim 23, wherein: The active implantable medical device is a cardiac stimulator.

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