Electromedical implant

0001The invention relates to an implantable medical device with a built-in transmitter / receiver (transceiver) for the wireless transmission and reception of data, which can be switched off between individual data transmissions.

0002Such implantable medical devices can be, for example, cardiac pacemakers or cardioverters / defibrillators or combinations of the two. In the meantime, a large number of such implants are known which have a transmitter / receiver, that is to say a transceiver, with the aid of which it is possible to transmit physiological or technical data or both from the implant to an external device or, conversely, using an external device to transmit data Transfer implant. The latter may be desirable, for example, for programming the implant or for querying certain data.

0003Basically, the problem with such implants is that the energy resources of the implant are limited and are usually given by a battery that is permanently installed in the implant. The basic task is therefore to limit the energy consumption of the implant as much as possible. This can happen, for example, by switching off components of the implant that are not currently being used. In this case, there is the further problem of how to switch these implant parts on again.

0004In addition, it must be taken into account that there may be several implants within mutual reach or within reach of one or more external devices.

0005The object of the invention is to provide an implant which is suitable for the aforementioned scenario and which is as energy-saving as possible.

0006According to the invention, this object is achieved by an implant of the type mentioned at the outset, which in addition to the transceiver has a wake-up unit which is designed to fully operate the transceiver from its idle state or from its switched-off state, in which it requires little or no energy Switch state in which he needs more energy accordingly. For this purpose, the wake-up unit has a second, separate low power receiver, which has a significantly lower energy requirement than the transceiver in its switched-on or fully operational state. In addition, the wake-up unit has a wake-up control unit which is connected to an output of the low power receiver. The low power receiver is designed to monitor a plurality of predetermined frequency ranges in such a way that, in the event of a sufficient signal strength being transmitted, it generates an output signal in one or more of the frequency ranges and outputs it to the wake-up control unit. The wake-up control unit is designed to evaluate output signals of the low power receiver and to emit a wake-up signal to the transceiver, which switches it on or fully operational if a predetermined condition is met or a plurality of predetermined conditions are met. The wake-up control unit is designed such that it then emits a wake-up signal to the transceiver when the low power receiver emits a sequence of output signals which indicate that the low power receiver has acquired a sequence of transmissions of sufficient signal strength in different frequency ranges. that correspond to a given sequence or sequence. If the frequency ranges monitored by the low power receiver are, for example, the frequency ranges A, B, C and D, the predetermined sequence or sequence can be such that the output signals are transmissions in the frequency ranges C, A, B, D (in this order) mark.

0007Such a sequence of transmissions in different frequency ranges is also referred to below as a trigger signal sequence, since such a sequence of transmissions is intended to trigger the switching on of the transceiver. The sequence of the output signals of the low power receiver thus always characterizes a respective frequency scheme. A frequency scheme serves as a key for switching on the transceiver of a correspondingly preset or programmed implant.

0008In addition or alternatively to the specification of a sequence, that is to say a frequency scheme, individual times can also be specified at which the signals must follow one another. If the sequence is specified as a substitute, for example, the wake-up unit alone can monitor the chronological sequence of signals on only one frequency band.

0009For the aforementioned purpose, the low power receiver preferably has a plurality of bandpass filters, the pass band of which is adapted to the predetermined frequency ranges. Each bandpass filter is assigned a signal detector which interacts with the respective bandpass filter in such a way that the signal detector outputs a signal when the low power receiver transmits with sufficient signal strength in a respective frequency range that corresponds to a pass band of the bandpass filter to which the signal detector is assigned receives. In such a low power receiver, an output signal is available at the output of a respective signal detector for forwarding to the wake-up control unit as soon as the low power receiver receives a transmission of sufficient signal strength in the respective frequency range. In this way, the low power receiver generates signals or signal sequences that are to be further processed by the wake-up control unit.

0010The wake-up control unit is preferably designed to detect the sequence of the signals output by the signal detectors and to compare them with a predetermined sequence in order to deliver the wake-up signal to the transceiver in the event of a positive comparison (the received signal sequence corresponds to the predetermined sequence).

0011In addition, the wake-up control unit can have a time monitoring unit and can be designed to generate the wake-up signal only when the signals output by the signal detectors occur in succession within a predetermined time period. The predefined time period can be a total time period within which all signals must have occurred, and there can also be a number of time periods that describe when a subsequent signal must follow the respective previous signal.

0012In all versions there is an implantable medical device, the transceiver of which can be switched from a switched-off or a power-saving mode to an switched-on or fully operational mode by receiving a trigger signal sequence, without the need to receive a signal of sufficiently good quality to receive the signal to be able to decode. A simple receiver is therefore sufficient as a low power receiver with low energy requirements. Nevertheless, a targeted response of a correspondingly preset implant is possible, even without first having to decode and evaluate, for example, corresponding address data in a received signal.

0013Another aspect relates to the reaction of the implant to the receipt of a trigger signal or a trigger signal sequence. If, for example, a plurality of implants are addressed simultaneously by a trigger signal sequence, this could result in all of the implants addressed sending a response signal to the carrier signal sequence simultaneously, so that successful communication with an external device is not possible, at least for the majority of the implants.

0014In order to counter this problem, the implantable medical device preferably has a transmission control unit, which has a random generator or is connected to it and is designed to send out a response signal after the waiting time after the transceiver has been switched on by the wake-up control unit, and also the time to determine a start of transmission after the transceiver has been switched on by the wake-up control unit, that the time of the start of the transmission corresponds to the end of the waiting time, which in turn begins with the wake-up signal. The waiting time has a duration that corresponds to the product ZZ x SD from a random number ZZ generated by the random number generator and a predetermined average transmission time SD.

0015In this way, it follows that the waiting time after which an implant reacts to a corresponding trigger signal has a random length, so that two implants are unlikely to respond to a trigger signal at the same time.

0016In addition, according to a preferred embodiment variant, if the random number is scaled such that it is an integer between 0 and a maximum number of implants to be expected in the reception range of an external device minus 1, it is also very unlikely that during the transmission period for the transmission of the response signal a first implant, a second implant starts sending a response signal.

0017Given a predetermined, maximum expected transmission time SD, this time period SD determines a timeslot for the transmission of the response signal. Since all implants in the vicinity of the external device are awakened by the same trigger signal on the part of the external device or - in a more general embodiment - are at least synchronized, the timeslots, that is to say the transmission duration times SD connected in series depending on the respective random number ZZ, are clocked in sync.

0018In such a scenario, due to the proximity of the implants to the external device, signal propagation times between the implants and the external device are negligible.

0019For such a scenario, there is a probability P for a maximum number of implants AI which is predetermined for all implants and which is in any case greater than the actual number n of implants_{AI, n}that all implants send in different timeslots as: <maths id="math0001" num=""><math display="block"><msub><mi mathvariant="normal">P</mi><mrow><mi>AI</mi><mo>,</mo><mi mathvariant="normal">n</mi></mrow></msub><mo>=</mo><msub><mi>P</mi><mrow><mi>A</mi><mo>⁢</mo><mi>I.</mi><mo>,</mo><mi>n</mi></mrow></msub><mo>=</mo><mfrac><mrow><msubsup><mi mathvariant="normal">Pi</mi><mi>i</mi><mrow><mi>A</mi><mo>⁢</mo><mi>I.</mi></mrow></msubsup><mo>=</mo><mi>A</mi><mo>⁢</mo><mi>I.</mi><mo>-</mo><mi>n</mi><mo>+</mo><msup><mn>1</mn><mi>i</mi></msup></mrow><msup><mrow><mi>A</mi><mo>⁢</mo><mi>I.</mi></mrow><mi>n</mi></msup></mfrac></math><img file="EP1892011A2_D0001.tif" /></maths>

0020For AI → ∞ this probability becomes P_{AI, n1,} that is, for a comparatively large number of AI, it is very likely that the implants each send in their own timeslot, ie do not send two implants in the same timeslot. This is independent of the length of the time slots specified by the maximum transmission time SD.

0021Since the probability that two implants will still send a response signal in the same timeslot is close to 0 but not equal to 0, the transmission control unit is designed in a preferred embodiment variant to repeat the transmission of the response signal after a new waiting time has elapsed. The repetition of sending the response signal may depend on whether a response signal sent in each case remains unanswered or not.

0022The invention will now be explained in more detail using an exemplary embodiment with reference to the figures. From the figures show:<dl id="dl0001" compact="compact"><dt>Figure 1:</dt><dd>exemplary a scenario with an external device and two implants within range of the external device;</dd><dt>Figure 2:</dt><dd>the structure of the transmitter and receiver unit of an implant; and</dd><dt>Figure 3:</dt><dd>a low power receiver, the transmitting and receiving unit of the implant from FIG. 2.</dd></dl>

00231 shows an external device as an external transceiver 10 and two implants 20 'and 20 ", which are located within a reception range of the external device 10 indicated by a broken line 12. The reception range results from the transmission power of the implants 20' and 20 "and the sensitivity of the receiver of the external device 10.

0024In connection with the scenario shown in FIG. 1, the problem arises, on the one hand, that the implants each have a transceiver 203 (see FIG. 2) which consumes a relatively large amount of energy in the transmit and receive mode and therefore in one unit for as long and as often as possible Energy saving mode should be kept or switched off, but at the same time it should also be possible to switch to its fully operational mode by a signal from outside the implant. However, if possible, this should not be done by signals that come from another implant or completely foreign transmitting device within the reception range of each device. If possible, the transceiver 203 of a respective implant should, if possible, only be woken up by an external device such as the external device 10.

0025The problem shown in FIG. 1 also gives rise to the problem that not both implants 20 'and 20 "can communicate wirelessly with the external device 10 in the same frequency range at the same time.

0026The implant 20 shown in FIG. 2 represents a preferred embodiment variant of an implant, which takes into account the two aforementioned problems.

0027On the one hand, the implant 20 has a wake-up unit 202, which is connected to the transceiver 203 of the implant 20 and can output a wake-up signal to the transceiver 203, by means of which the transceiver 203 fully switches from a switched-off state or an energy-saving mode to a more energy-intensive mode ready mode can be switched.

0028The wake-up signal, which the wake-up unit 202 emits to the transceiver 203, should be able to be triggered wirelessly, but not by any data transmission. In addition, the reception of a wirelessly transmitting trigger signal which triggers the wake-up signal should not already require as much energy as the transceiver 203 requires in its fully operational state.

0029In order to achieve this, the wake-up unit 202 has, in addition to a wake-up control unit 207, which ultimately generates the wake-up signal, a low power receiver 210 which, as a broadband receiver, is able to detect wireless transmissions of signals in different frequency ranges. Specifically, the low power receiver 210 is able to detect transmissions that each exceed a minimum, predetermined signal strength in one of a plurality of predetermined frequency ranges and to generate an output signal if it transmits a signal strength in one of the predetermined frequency ranges recorded above the specified minimum.

0030For this purpose, the low power receiver (see FIG. 3) has four bandpass filters 211 ', 211 ", 211"' and 211 "", each of which has a pass band (passband), which is tuned to a frequency range of a total of four frequency ranges. Each bandpass filter 211 ', 211 ", 211"' and 211 "" is followed by a signal detector 212 ', 213', 212 ", 213", 212 "', 213"', 212 "", 213 "". Each of these signal detectors has a threshold switch 212 ', 212 ", 212'" and 212 "" which is responsive to an output signal at a signal strength at the output of the corresponding bandpass filter 211 ', 211 ", 211"' or 211 "" is present, which lies above the predetermined threshold. If the respective threshold switch 212 ', 212 ", 212'" or 212 "" responds accordingly to such a signal, it triggers a respective monostable flip-flop (monoflop) connected downstream of the threshold switch 212 ', 212 ", 212'" or 212 "". 213 ', 213 ", 213"' or 213 "". In this way, the respective monostable multivibrator 213 ', 213 ", 213"' or 213 "" generates an output signal which characterizes that given in the pass band of the respective bandpass filter 211 ', 211 ", 211"' or 211 "" Frequency range a transmission of signals with a signal strength above the predetermined minimum has taken place. In this way, the output signals of the monostable multivibrators 213 ', 213 ", 213"' and 213 "", which are at the same time output signals of the low power receiver 210, identify by their sequence the order in which transmissions in different frequency ranges by the low power receiver 210 are received.

0031The wake-up control unit 206 is designed to evaluate the output signals of the low power receiver 210 in two ways. On the one hand, the wake-up control unit is designed to compare the sequence of the output signals of the low power receiver 210 with a predetermined sequence and to only output the wake up signal to the transceiver 203 if the sequence of the output signals of the low power receiver 210 corresponds to the predetermined, in Implant 20 corresponds to the stored order. In addition, the wake-up control unit 206 is designed to use a time monitoring unit 207 to ensure that the wake-up signal is only generated when the output signals of the low power receiver 210 follow one another not only in the predetermined order but also within a predetermined time arrive.

0032The predetermined sequence of the signals and the corresponding predetermined times result in a type of characteristic key with which, for example, an external device can wirelessly wake up a transceiver 203 of an implant 20 without the need to decode and evaluate data, for example as address data a wirelessly transmitted signal.

0033A transmission control unit 204 of the implant 20 is designed to control the transmission of a response signal which the implant 20 emits after receipt of a wirelessly transmitted trigger signal which has led to a wake-up of the transceiver 203 via a corresponding wake-up signal. The transmission control unit is designed to initiate transmission of the response signal via the transceiver 203 only after a waiting time has elapsed, which begins when the transceiver 203 is woken up. The transmission control unit 204 calculates this waiting time from a random number ZZ generated by a random generator 205 and a predetermined maximum value for a transmission duration SD for sending the response signal B from a likewise predetermined integer AI, which is greater than the maximum number of implants to be expected within the range of an external device.

0034From the random number ZZ scaled to integers between 0 and AI-1 and the specified maximum transmission time SD stored in the implant, the waiting time is formed as a product of the integer random number ZZ and SD scaled with AI: ZZ x SD.

0035The respective waiting time determined in this way is started upon receipt of the carrier signal and leads to the control unit 204 triggering the transmission of the response signal via the receiver 203 at the end of the waiting time.

0036As previously explained, it is highly unlikely that more than one implant within range of an external device will respond to a trigger signal sent from the external device at the same time if SD is greater than the send time for sending the response signal and if AI is greater than the maximum number of implants that are within the range (indicated by the broken line 12 in FIG. 1) of the external device 10.

0037This effectively prevents two implants from responding to a trigger signal at the same time.