(19) United States
`(12) Patent Application Publication (10) Pub. No.: US 2008/0242962 A1
`Roesicke et al.
`(43) Pub. Date:
`Oct. 2, 2008
`
`US 20080242962A1
`
`(54) SYSTEM FOR IN-VITRO MEASUREMENT OF
`AN ANALYTE CONCENTRATION
`
`(76) Inventors:
`
`Bernd Roesicke, Mannheim (PE):
`Karin Obermaier, Bruehl (DE):
`
`Stefan Lindegger, Lotzwil (CH):
`
`Andreas Menke, Mannheim (DE);
`Joerg Scherer, Gudensberg (DE);
`Karin Schwind, Schifferstadt (DE);
`Otto Gaa, Worms (DE); Gregor
`Bainczyk, Mannheim (DE);
`Michael Marquant, Mannheim
`(DE); Sandro Niederhauser,
`Rutschelen (CH); Michael
`Schoemaker, Mannheim (DE);
`Martin Mueri, Basel (CH)
`
`Correspondence Address:
`ROCHE DAGNOSTICS OPERATIONS INC.
`9115 Hague Road
`Indianapolis, IN46250-0457 (US)
`
`(21) Appl. No.:
`
`12/052.382
`
`
`
`Mar. 20, 2008
`(22) Filed:
`Foreign Application Priority Data
`(30)
`Mar. 20, 2007 (EP) .................................. 07.005638.7
`Dec. 13, 2007 (EP)
`O7024174.O
`
`• u - s 1- w
`
`wu u f
`
`· · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · ·
`
`Publication Classification
`
`(51) Int. Cl.
`(2006.01)
`A6B 5/55
`(52) U.S. Cl. ........................................................ 6OO/347
`(57)
`ABSTRACT
`The analyte concentration, such as glucose, in a human or
`animal body is measured with an implantable sensor that
`generates measurement signals. The measurement signals are
`compressed through statistical techniques to produced com
`pressed measurement data that can is easier to process and
`communicate. A base station carries the implantable sensor
`along with a signal processor, memory, and a transmitter. A
`display device is also disclosed that can receive the com
`pressed measurement data from the base station for further
`processing and display.
`
`Page 1 of 17
`
`

`

`Patent Application Publication
`
`Oct. 2, 2008 Sheet 1 of 6
`
`US 2008/0242962 A1
`
`
`
`/ 1
`
`
`
`Fig. 1
`
`Page 2 of 17
`
`

`

`Patent Application Publication
`
`Oct. 2, 2008 Sheet 2 of 6
`
`US 2008/0242962 A1
`
`o
`N
`
`g
`
`
`
`Page 3 of 17
`
`

`

`Patent Application Publication
`
`Oct. 2, 2008 Sheet 3 of 6
`
`US 2008/0242962 A1
`
`
`
`
`
`
`
`
`
`
`
`*ts
`
`V
`
`V
`
`(this in
`
`2
`
`Y
`
`
`
`-
`
`Page 4 of 17
`
`

`

`Patent Application Publication
`
`Oct. 2, 2008
`
`Sheet 4 of 6
`
`US 2008/0242962 A1
`
`
`
`Page 5 of 17
`
`

`

`Patent Application Publication
`
`Oct. 2, 2008 Sheet 5 of 6
`
`US 2008/0242962 A1
`
`
`
`66
`
`Fig. 8
`
`Page 6 of 17
`
`

`

`Patent Application Publication
`
`Oct. 2, 2008 Sheet 6 of 6
`
`US 2008/0242962 A1
`
`
`
`Page 7 of 17
`
`

`

`US 2008/0242962 A1
`
`Oct. 2, 2008
`
`SYSTEM FOR IN-VITRO MEASUREMENT OF
`AN ANALYTE CONCENTRATION
`
`REFERENCE
`0001. This application claims priority to European Patent
`Application No. EP 07 005 638.7 filed Mar. 20, 2007 and
`European Patent Application No. EP 07024174.0 filed Dec.
`13, 2007, which are both hereby incorporated by reference.
`
`FIELD
`0002 This disclosure relates to a system for in-vitro mea
`Surement of an analyte concentration in a human or animal
`body.
`
`BACKGROUND
`0003 Systems of this type for in-vivo measurement of
`analyte concentrations usually comprise replaceable sensors
`as replaceable or consumable components and a long-lived
`base station to which the replaceable sensors are connected.
`An example of such system is disclosed in US 2004/
`1O133164 A1.
`0004 In-vitro measurement system can be monitor ana
`lyte concentration over many hours or days generate large
`amounts of data that can be difficult to store and transmit.
`
`SUMMARY
`0005. The measure according to embodiments the inven
`tion to have the analytical unit of the base station, in opera
`tion, Subject to statistical analysis the measuring signals that
`are Supplied as raw data by a sensor connected to it and
`generate from the raw data condensed measuring data for
`transmission by the transmitter to the display device, and to
`have the display device contain an electronic analytical unit,
`which, in operation, determines an analyte concentration
`value by analyzing the condensed measuring data, allows the
`volume of data to be transmitted and therefore the energy
`consumption to be kept advantageously low while the advan
`tage of a high measuring rate can still be utilized.
`0006. In order to keep the weight of the system compo
`nents that are carried on the body as low as possible, it is
`advantageous for the energy consumption of the base station
`to be as low as possible, since a smaller and lighter-weight
`battery is then Sufficient for Supplying this system component
`with energy for a sufficiently long period of time.
`0007 Preferably, measuring or sensor signals that are sup
`plied by a sensor are recorded for first time intervals, for
`example of duration from 0.5 seconds to 5 seconds, as raw
`data. The raw data are then used to generate condensed mea
`Suring data for second time intervals, for example of 10 to
`1,000 seconds, whereby the second time intervals are at least
`10-fold, preferably at least 50-fold, longer than the first time
`intervals. Preferably, both the first time intervals and the
`second time intervals each are invariable.
`0008 Accordingly, exactly one measuring signal value
`that is correlated to the analyte concentration to be deter
`mined is stored in the base station for a first time interval. In
`order to reduce the energy consumption associated with the
`transmission of data, it is preferred to generate from each at
`least 10, in particular at least 50, signal values that are stored
`as raw data a condensed measuring data value for a corre
`spondingly larger time interval.
`0009 Measuring signals can be generated in very short
`time intervals of for example, one second through the use of
`
`implantable sensors such that very large Volumes of raw data
`may be obtained upon Sustained measuring. Another aspect of
`embodiment of the invention, which may be of significance
`independently, relates to a method for condensing raw data
`that were determined using an implanted sensor, in which
`method pairs of measuring signal values are formed from the
`raw data generated for a time interval, then a slope of a line
`connecting the two values of a pair of values is determined for
`each pair of measuring signal values, then a median value of
`the slopes thus determined is calculated, and then a con
`densed data value is calculated for said time interval from the
`median value of the slope and the condensed data value of the
`preceding time interval.
`0010 Since, initially, no condensed data value is available
`for the first time interval, the median or, for example, the
`arithmetic mean of the raw data values determined for the first
`time interval may be used as condensed data value of the first
`time interval. Raw data values that are non-plausible, for
`example due to uncommonly strong deviation from the
`remaining raw data values of a time interval, can be disre
`garded in the determination of the condensed data value, for
`example in that they are not used for forming pairs of values.
`0011
`Preferably, the measuring signals supplied by a sen
`sor are condensed as raw data in the base station into measur
`ing data in a first step of analysis, the condensed measuring
`data are transmitted to the display device, and analyte con
`centration values are calculated from the measuring data by
`means of the analytical unit of the display device in a further
`step of analysis. Having a two-step analysis of this type
`including a first step of analysis in the base station and a
`further step of analysis in the display device allows the advan
`tages of continuous or quasi-continuous measurement with
`regard to currentness and accuracy to be utilized and still keep
`the data volumes to be transmitted by the base station small.
`In particular, relatively simple and therefore cost-efficient
`microprocessors in the base station are sufficient for condens
`ing the raw data, for example by forming the mean or by
`application of the repeated median procedure. For final analy
`sis of the condensed measuring data, a powerful and more
`expensive microprocessor can be used in the display device,
`and can be used thereinfor other tasks as well, for example for
`a graphic presentation of the analyte concentration values
`thus determined and linking to other data that have been
`generated and stored by the display device or originate from
`other sources. Therefore, another aspect of the invention that
`may also be of significance independently relates to a system
`for in-vivo measurement of an analyte concentration in a
`human or animal body having at least one implantable sensor
`for generating measuring signals that are correlated to the
`analyte concentration to be measured, a base station that can
`be connected to the sensor and contains an electronic analyti
`cal unit for analysis of measuring signals of a sensor con
`nected to it, and a transmitter for wireless transmission of
`analytical results, and a display device that comprises a
`receiver for receiving the analytical signals transmitted by the
`base station and a display facility for displaying analyte con
`centration values, whereby the analytical unit of the base
`station, in operation, Subjects the raw data Supplied by a
`sensor connected to it to statistical analysis and generates
`from the raw data condensed measuring data that are then
`transmitted by the transmitter to the display device, and the
`display device contains an electronic analytical unit that, in
`operation, determines an analyte concentration value by
`analysis of the measuring data.
`
`Page 8 of 17
`
`

`

`US 2008/0242962 A1
`
`Oct. 2, 2008
`
`0012. Therefore, a further aspect of embodiments of the
`invention that may be of significance independently relates to
`a system for in-vivo measurement of an analyte concentration
`in a human or animal body having at least one implantable
`sensor for generating measuring signals that are correlated to
`the analyte concentration to be measured, a base station that
`can be coupled to the sensor and contains a potentiostat for
`Supplying Voltage to a sensor of this type, as well as a receiver
`and a transmitter for wireless transmission of data, whereby
`the base station is adapted Such that the transmission of data
`is initiated by receiving a control signal that is transmitted by
`wireless means. In order to prevent miscommunication with
`devices that are not part of the system, the control signal can
`include a characteristic identifier that is used by the sampling
`device to identify itself with respect to the base station. Like
`wise, the base station can transmit a characteristic identifier
`signal when it communicates in order to identify itself.
`0013 The data can, in particular, be condensed measuring
`data that have been determined by an analytical unit that is
`contained in the base station from raw data that was obtained
`as measuring signals of a connected sensor. A control signal
`initiating transmission of the measuring data can, for
`example, be transmitted by a display device.
`0014. In systems for in-vivo measurement of analyte con
`centrations, for example glucose, sensors usually need to be
`replaced every few days. Replacing a sensor and correctly
`connecting a new sensor to the base station prove to be cum
`berSome for many users, in particular for patients whose
`manual dexterity is restricted due to age or disease. By having
`the sensor be part of a replaceable sensor carrier unit that
`comprises a sealed housing in which the sensor is disposed,
`and having the housing of the sensor carrier unit lock to the
`base station in order to couple the sensor to the base station,
`the handling of the system, in particular the replacing of
`sensors, can be simplified significantly such that a system
`according to the invention can, in particular, be used by medi
`cal laymen also.
`0015 The sealed housing of the sensor carrier unit pro
`tects the sensitive sensor from adverse environmental influ
`ences. For this reason, the sensor carrier unit can be handled
`by laymen also without a risk of damaging or contaminating
`the sensor. Coupling the sensor carrier unit to the base station
`is made easy by locking. The sensor can be exposed for
`insertion after coupling, for example by means of a predeter
`mined breaking point for the sensor that is provided on the
`housing of the sensor carrier unit.
`0016. The sensor can be coupled electrically to the base
`station by means of a data line, for example in the case of
`electrochemical sensors being used. If optical sensors are
`used, such as those known from U.S. Pat. No. 6,584,335, the
`sensor can just as well be coupled to the base station by means
`of an optical data line.
`0017. However, it is also feasible for the sensor carrier unit
`to communicate with the base stationina wireless fashion, for
`example inductive or by means of RFID. Having wireless
`communication between sensor carrier unit and base station
`is advantageous in that sealing problems of the sensor carrier
`unit and base station, which are carried on the body by the
`patient, are largely prevented. In particular, the risk of leakage
`current interfering with measuring results can also be
`reduced. A wireless communication between the sensor car
`rier unit and the base station locked to it, i.e. over a very short
`distance, can be implemented in a cost-efficient fashion, for
`example by means of inductive coupling. A relatively cost
`
`intensive transmitter with a larger range of for example, one
`meter for communication with the display device is only
`needed in the base station.
`0018. The sensor carrier unit preferably contains a data
`carrier bearing calibration data of the sensor. This measure is
`advantageous in that it ensures reliably that data determined
`by a sensor are always analyzed using matching calibration
`data. In particular in the case of a sensor carrier unit that
`communicates with the base station in a wireless fashion, it
`can be advantageous to dispose in the housing of the sensor
`carrier unit a data carrier onto which calibration data can be
`written through the sealed housing of the sensor carrier unit,
`for example an electronic memory that can also be read and/or
`written to by means of RFID. By this means it is feasible to
`sterilize the entire sensor carrier unit by exposure to radiation,
`determine the needed calibration data after the sterilization
`process using random samples of a production hatch, and then
`write the calibration data onto the data carriers of the sensor
`carrier units. It is also feasible, though, to dispose the sensor
`in a first chamber and the data carrier in a second chamber of
`the sensor carrier unit. By this means, the sensor can be
`sterilized inside a sealed chamber and a data carrier bearing
`calibration data can be inserted in the second chamber sub
`sequently.
`0019. The sensor carrier unit preferably contains a battery.
`This battery can, in particular, also be used for Supplying
`power to the base station Such that consumable components
`of the system according to the invention can advantageously
`be combined in the sensor carrier unit. It is particularly pre
`ferred for the battery to be surrounded by the housing of the
`sensor carrier unit. This measure is advantageous in that the
`battery is well-protected and manipulations by users are made
`more difficult.
`0020. In a system according to the invention, the base
`station preferably comprises a housing that is adjusted to
`match the sensor carrier unit and comprises an interface that
`matches the interface of the sensor carrier unit such that the
`sensor becomes electrically connected to the base station by
`placing the housing of the base station against the housing of
`the sensor carrier unit. A reversible, i.e. Subsequently releas
`able, coupling of the sensor carrier unit to the base station can
`be implemented, for example, by means of a form-fitting or a
`non-positive connection. In this context, it is particularly
`advantageous and therefore preferred for the sensor carrier
`unit to lock to the base station since this can be perceived by
`a user Such that it is thus signaled to him that the sensor carrier
`unit is correctly connected to the base station.
`0021. The sensor can, for example, be an amperometric
`sensor that is Supplied with power by a potentiostat that is
`contained in the base station. However, electrochemical sen
`sors needing no potentiostat can be used for the system just as
`well, for example coulomb-metric sensors or, for example,
`optical sensors.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`0022. Further details of embodiments of the invention are
`illustrated by means of exemplary embodiments and refer
`ence being made to the appended drawings.
`0023 FIG. 1 shows a schematic view of an exemplary
`embodiment of a system according to the invention for in
`Vivo measurement of an analyte concentration in a human or
`animal body;
`
`Page 9 of 17
`
`

`

`US 2008/0242962 A1
`
`Oct. 2, 2008
`
`0024 FIG. 2 shows a schematic view of the interaction of
`the system components of the exemplary embodiment shown
`in FIG. 1;
`0025 FIG. 3 shows an exemplary embodiment of a base
`station and a sensor carrier unit of a system according to FIG.
`1 connected to it;
`0026 FIG. 4 shows a cross-sectional view related to FIG.
`3:
`0027 FIG. 5 shows a sensor housing of the exemplary
`embodiment shown in FIGS. 3 and 4:
`0028 FIG. 6 shows components of a further exemplary
`embodiment;
`0029 FIG. 7 shows a longitudinal sectional view of the
`components shown in FIG. 6 in the assembled state;
`0030 FIG. 8 shows a base plate of the exemplary embodi
`ment shown in FIG.7 having an insertion aid for application
`of the sensor in the body of a patient;
`0031
`FIG. 9 shows a longitudinal sectional view through
`the base plate shown in FIG. 8 having the insertion aid placed
`on it, before application of the sensor, and,
`0032 FIG.10 shows alongitudinal sectional view through
`the base plate shown in FIG. 8 having the insertion aid placed
`on it, after application of the sensor.
`
`DETAILED DESCRIPTION
`0033 FIG. 1 shows a schematic view of a system 1 for
`in-vivo measurement of an analyte concentration in a human
`or animal body. The system 1 includes, as consumable or
`replaceable component, a sensor carrier unit 10 having at
`least one implantable sensor 3 for generating measuring sig
`nals that are correlated to the analyte concentration to be
`measured. The sensor carrier unit 10 has a housing 12 that is
`shown in FIG. 3 to have a bottom 27 that extends along the
`body surface when the sensor carrier unit 10 is attached to the
`body of a patient according to its purpose. The sensor carrier
`unit 10 contains a battery 5 and a data carrier 11 bearing
`calibration data of the sensor 3. The battery 5 and the data
`carrier 11 are disposed within the housing 12 of the sensor
`carrier unit 10 such as to be inaccessible to a user in order to
`exclude, to the extent possible, erroneous results or damage
`from inappropriate handling.
`0034. The sensor carrier unit 10 can be connected to a base
`station 2 by meals of a catch mechanism. The base station 2 is
`a multiply usable component of the system 1. A spent sensor
`carrier unit 10 can be uncoupled from the base station 2 and
`replaced by a new sensor carrier unit 10. The base station 2
`contains a potentiostat 48 for Supplying Voltage to a sensor 3
`of a sensor carrier unit 10 connected thereto, an electronic
`analytical unit 47 for analysis of measuring signals of a sensor
`3 connected thereto, and a communication unit 31 having a
`transmitter for wireless transmission of analytical results. The
`base station 2 further contains an electronic intermediary
`memory 60 for storing measuring values or data obtained
`therefrom. In the exemplary embodiment shown, the base
`station 2 contains a memory for intermediate storage of raw
`data, for example a RAM memory, and a memory for storing
`condensed measuring data, for example an EEPROM or flash
`memory, until Such data is transmitted and/or for the storage
`of data that were passed on to the base station 2 by the display
`device 4.
`0035. The sensor carrier unit 10 has a housing 12 having
`an interface for electric connection of the sensor 3 to the base
`station 2. In corresponding fashion, the base station 2 has a
`housing that is adapted to match the sensor carrier unit 10 and
`
`comprises an interface that matches the interface of the sensor
`carrier unit 10 such that the sensor 3 can be connected elec
`trically to the potentiostat 48 by placing the housing of the
`base station 2 against the housing 12 of the sensor carrier unit
`10 such that sensor contacts 3a, 3b, and 3c are connected to
`connections 6a, 6b, and 6c of the base station. In the process,
`the battery 5 and the data carrier 11 are also connected to
`contacts 7a, 7b and 8a, 8b, respectively, of the interface of the
`base station 2. The mutually matching interfaces of the sensor
`carrier unit 10 and base station 2 can form a plug-in connec
`tion whereby the in male part of the plug-in connection can be
`disposed on the base station 2 and the female part on the
`sensor carrier unit 10 or vice versa.
`0036) A start-up is caused by connecting the sensor carrier
`unit 10 to the base station 2, in particular the measuring
`process of sensor 3 is initiated in this way. Accordingly, the
`sensor 3 is activated by coupling to the base station 2 Such that
`it commences to Supply measuring signals. A reset and ini
`tialization command for this purpose can be effected in a
`processor forming the analytical unit 47 upon connecting the
`sensor carrier unit 10 to the base station 2. This measure is
`advantageous in that no Switch is required to Switch-on the
`system and the start-up of the system is effected by a defined
`action of the user, namely by connecting a sensor carrier unit
`10 to the base station 2. As soon as a Voltage is applied by
`connecting the battery to the potentiostat 48, charge carriers
`are automatically transported away from the working elec
`trode such that the risk of charge accumulation is minimized.
`0037. A further long-lived component belonging to the
`system is a display unit 4 that comprises a receiver 30 for
`receiving the data transmitted by the base station 2, and a
`display facility 29, for example a liquid crystal display, for
`displaying analyte concentration values. The receiver 30 of
`the display device 4 preferably also contains a transmitter and
`the transmitter 31 of the base station also contains a receiver
`Such that abidirectional communication between base station
`2 and display device 4 is feasible. Transmissions of the base
`station 2 and of the display device 4 can be characterized by
`means of an identifier, for example a bit sequence. In order to
`exclude miscommunication with devices of other patients,
`signals that do not bear the expected identifier may be ignored
`by the base station 2 and the display device 4.
`0038. The distribution of functions and components to the
`system components, sensor carrier unit 10, base station 2, and
`display device 4, as described, allows an optimal result to be
`attained with regard to the weight of the system components
`that are to be carried on the body, the costs, and the user
`convenience. Consumable components of the system, for
`example sensor 3 and battery 5, are part of the sensor carrier
`unit 10 that needs to be replaced periodically, for example
`every 5 days, such that all consumable components can be
`replaced as easily as possible. In order to generate measuring
`data using a sensor 3 of the sensor carrier unit 10, aside from
`the consumable components, long-lived system components,
`Such as for example the potentiostat 48 and an analytical unit,
`are also required. The distribution of these long-lived system
`components to the base station 2, which is also carried on the
`body, and the display device 4 was effected to provide the
`best-possible user convenience in order to be able to imple
`ment the base station 2 to be as Small and lightweight as
`possible. For this reason, the base station 2 contains a poten
`tiostat 48 for Supplying a sensor 3 connected to it, a transmit
`ter for transmitting data to the display device 4, and an ana
`lytical unit 48 for preliminary analysis of the measuring data
`
`Page 10 of 17
`
`

`

`US 2008/0242962 A1
`
`Oct. 2, 2008
`
`Supplied by a sensor connected to it. The base station 2 needs
`to have no own display facility since this function is assumed
`by the display device 4. Having a preliminary analysis in the
`base station 2 in combination with a final analysis in the
`display device 4 allows the volume of data to be transmitted to
`be kept low. Accordingly, the base station 2 needs just a small
`memory, a simple analytical unit, and little energy Such that a
`patient is required to carry as little mass as possible on the
`body.
`0039. The display device 4 can be equipped with a large
`memory and complex analytical electronics, in particular a
`powerful microprocessor, and therefore can perform even
`extensive mathematical analyses of data over long periods of
`time. In particular, the display device 4 can test for a newly
`implanted sensor whether or not the new sensor works prop
`erly by means of a comparison with measuring data of earlier
`sensors or defined level and/or gradient values and form fac
`tors or samples. Moreover, the display device 4 allows its user
`the convenient entry of patient data, for example individual
`threshold values, whereby the display unit 4 can generate a
`warning signal when these are exceeded or not reached. In
`addition to an analytical, display, and warning function, the
`display device 4 can also assume the function of a data and
`communication center with regard to further components of
`the system, for example an injection device.
`0040. According to its purpose, the base station 2 and the
`sensor carrier unit 10 are carried on the body by a patient
`during the in-vivo measurements. In the process, the electro
`chemical sensor 3 projects into the body of the patient and is
`supplied by the potentiostat 48 that is contained in the base
`unit. While measuring, a current flows between the working
`electrode and the counter-electrode of the sensor 3 with its
`amplitude being correlated to the analyte concentration to be
`measured, such as being proportional to it in an ideal case. In
`the process, the potentiostat 48 varies the electrical potential
`applied to the counter-electrode such that the potential of the
`reference electrode of the sensor 3 remains constant.
`0041. The system 1 shown can be used to monitor an
`analyte concentration in the body of a patient in a continuous
`or quasi-continuous fashion. This means that the sensor 3 can
`be used to perform measurements in short time intervals of
`less than 5 minutes, in particular of less than 1 minute or even
`less than 10 seconds. A measurement can be effected in this
`context by means of digitizing a raw signal, for example an
`electrical current, in order to generate a measuring signal.
`Further data can be collected simultaneous with these mea
`Surements, for example temperature and/or electrode Volt
`ages that can be used for plausibility checking and/or error
`compensation.
`0042. Measurements are taken in the system 1 described
`here at time intervals of approx. one second, for example
`between 0.5 and 2 seconds, such that very large volumes of
`raw data accrue. The measuring signals Supplied by the sensor
`3 in time intervals of this type can be values of a continuous
`signal that has already been amplified and/or filtered, for
`example using a low-pass filter, in order to filter out electrical
`interference Such as can be generated by the frequency of the
`public electrical power network (50 Hz or 60 Hz), noise or
`radio communication. The cut-off frequency of a low-pass
`filter of this type is preferably between 3 Hz and 50 Hz, in
`particular between 5 Hz and 20 Hz. In this context and in
`accordance with general usage, cut-off frequency is under
`stood to mean the frequency at which the low-pass filter
`effects 3 dB of attenuation.
`
`0043. Low-frequency interference in the measuring sig
`nals that may arise, for example, from disturbances of the
`electrochemistry at interfaces between the sensor and Sur
`rounding body tissue, can be removed by means of filter
`algorithms, for example, by the repeated median procedure
`described in the application.
`0044. The measuring signals Supplied by a sensor 3 being
`in operation are subjected to a preliminary analysis by the
`analytical unit 47 that is contained in the base station 2. In the
`process, the measuring signals are subjected to statistical
`analysis as raw data and condensed measuring data are thus
`produced from the raw data. The condensed measuring data
`are generated by the base station 2 for constant consecutive
`time intervals of, for example, one minute such that an unam
`biguous assignment of the time of the measuring data exists
`that results from the sequence and size of the time intervals.
`Subsequently, the condensed measuring data are transmitted
`in a wireless fashion to the display device 4 and further
`analyzed therein by means of an analytical unit, for example
`a microprocessor, in order to determine analyte concentration
`values.
`0045. In the exemplary embodiment shown, the base sta
`tion 2 contains a memory in which the condensed measuring
`data can be stored such that they need not be transmitted right
`after being generated. The data sets stored can be provided
`with a check code that allows the condensed measuring data
`to be checked for data corruption and erroneous measuring
`data to be recognized in Subsequent steps of analysis. Status
`information of the base station 2, for example the charge
`status of the battery, results of internal functional tests and
`similar information can also be stored in the memory jointly
`with the measuring data. This status information can be stored
`as status code, for example as byte, and taken into account in
`the analysis.
`0046 Particularly efficient storage of the condensed mea
`Suring data can be attained by storing only the deviation from
`a preceding measuring data value as the measuring data value.
`By this means, it is sufficient to fully store the first measuring
`data value in the memory. All Subsequent values can then be
`characterized unambiguously by their difference from the
`preceding measuring data value Such it is sufficient to store
`this difference.
`0047. The measuring signals to be condensed are stored
`only temporarily as raw data in the base station until the
`condensed measuring data are generated. The base station 2
`therefore comprises a raw data memory whose content is
`overwritten as soon as a condensed measuring data value was
`determined for the measuring signals of a time interval and
`there is no longer a need for the measuring signals. It may be
`advantageous for some applications to provide for the option
`of later access to the raw data. This can be attained, for
`example, by transmitting raw data prior to over-writing them.
`This transmission can proceed unidirectional, i.e. without the
`reception of such data being confirmed by means of a receiv
`ing signal by a receiving device that stores the raw data. The
`base station 2 can comprise an additional transmitter for
`unidirectional transmissions.
`0048 FIG. 2 shows a schematic view of the interaction of
`the various system components. To the left of the dashed line
`are shown the sensor 3 and components of a base station 2
`connected thereto, whereas components of the display device
`4 are shown to the right of the dashed line.
`0049. The base station 2, in operation, supplies the sensor
`3 with voltage 49 of an amplitude that can depend on calibra
`
`Page 11 of 17
`
`

`

`US 2008/0242962 A1
`
`Oct. 2, 2008
`
`tion data 50 that are stored on the data carrier 11 shown in
`FIG. 1. The sensor 3 supplies measuring signals 32 that are
`being digitized by an analog-digital converter 33 and Subse
`quently subjected to statistical analysis as digital raw data 51
`by the analytical unit 47, preferably a microprocessor. In the
`process, condensed measuring data 36 are generated from the
`raw data 51. The condensed measuring data 36 are placed in
`a memory 35 that can be accessed both by the analytical unit
`47 and the communication unit 31 that contains a transmitter
`and a receiver. In order to prevent access conflicts, the ana
`lytical unit 47 and the communication unit 31 are connected
`to the memory 35 by means of a changeover switch 34 which
`provides access to the memory 35 either to the analytical unit
`47 or to the communicat