WO2007104531A1

WO2007104531A1 - A method and a medical device for calculating a checksum value so as to determine whether a displayed dose corresponds to a set dose

Info

Publication number: WO2007104531A1
Application number: PCT/EP2007/002204
Authority: WO
Inventors: Michael Enggaard Pedersen
Original assignee: Novo Nordisk A/S
Priority date: 2006-03-13
Filing date: 2007-03-13
Publication date: 2007-09-20

Abstract

A medical device comprising a processor programmed to generate a checksum value for a displayed dose and to relate the generated checksum value to a reference checksum value so as to determine whether a displayed dose corresponds to a set dose. A method for performing, on the medical device, the steps of: determining a set dose; displaying the set dose; retrieving dose displaying information from the display; generating a checksum value for a segment of the display; and relating the generated checksum value to one or more reference checksum value(s).

Description

A METHOD AND A MEDICAL DEVICE FOR CALCULATING A CHECKSUM VALUE SO AS TO DETERMINE WHETHER A DISPLAYED DOSE CORRESPONDS TO A SET DOSE

FIELD OF THE INVENTION The present invention relates to a medical device programmed to determine whether a displayed dose corresponds to a set dose. In particular the present invention relates to a medical device which is programmed to generate a checksum value for at least a part of a display and to relate the generated checksum value to a reference checksum value. Moreover, the present invention relates to a method of verifying a dose set on a medical device. In particular the method comprises the steps of generating a checksum value and relating it to a reference checksum value.

BACKGROUND OF THE INVENTION

Medical devices for administering a dose of a medicament are known in the art. Such devices may comprise means for setting a dose and a processor for determining the set dose.

US 6,277,098 discloses an injection device with signal generators which are connected to operative elements of the device. Signals from the signal generators are sent to an electronic circuit which controls a presentation of the operational condition of the device and which switches off the display or disables the device, when detecting an error in the switches or generators. US 6,277,098 defines operative elements as "elements for setting and injecting of set doses of medicine" and generators as "switches switching on and off a current" and "active current generators".

Further background art may be seen in US 5 406 301, EP 0 132 925, US 6 281 929, US 6 839 055, US 5 958 080 and EP 1 191 342.

A user operating a medical device with correctly functioning dose setting means may, however, inject a wrong dose by accident if the display of the medical device is not functioning correctly. Such a malfunctioning display, may cause the user to believe that a first dose is set while in fact a second dose - different from the first dose - is set. As an example, the user may believe that he has set a dose of 10 units - as displayed in the display - while he in fact he has set a dose of 70 units, which due to malfunctioning of the display is not displayed as 70 units but as 10 units. It will be appreciated that such an error in the display may have serious consequences for the user - depending on the type and concentration of the medicament. Accordingly, it is an object of a preferred embodiment of the present invention to provide a medical device which is adapted to determine the displayed dose and to determine whether the displayed dose and the set dose are identical.

As resolution of displays increases, the requirements of computation power of a processor arranged to determine whether the displayed information corresponds to the set information increases. Accordingly, it is an object of the present invention to provide a medical device wherein a processor is adapted to handle large quantities of information in a rationalised manner.

BRIEF SUMMERY OF THE INVENTION In a FIRST aspect the present invention relates to a medical device for ejecting a dose of a medicament, the device comprising: an input device adapted to determine a set dose and to output a signal comprising dose-setting information relating to the set dose; and a processor programmed to collect the dose-setting information and to display the set dose on a display, the processor being programmed to collect dose-displaying information from the display, said dose-displaying information relating to the displayed dose, the processor being programmed to generate a checksum value on the basis of at least a part of the dose-displaying information and to relate the generated checksum value to at least one reference checksum value so as to determine whether the displayed dose corresponds to the set dose.

In devices according to the present invention, the process of comparing a displayed dose with a set dose is simplified as a checksum value is generated for at least a part of the displayed information and said checksum is compared with a reference checksum. This is highly advantageous in connection with displays having a large number of pixels/segments, as a pixel-for-pixel comparison is transformed into a generation of one checksum and a comparison between the generated checksum and a reference checksum. This is more efficient and reduces processing time. Moreover, for each possible pattern/character/number displayed on the display, the storage of checksums requires less memory than storage of pixel-for-pixel values for each pattern/character/number.

The medical device may be a syringe, a motordoser, a jet-injector an inhalator, a pump for administering a medicament such as an insulin pump.

In the context of the present invention the term "processor" shall be understood as any unit capable of performing logic operations, and, thus, includes - but is not limited to - integrated circuits comprising a plurality of logic gates/units and any programmable unit such microcontrollers. In one embodiment the processor comprises a combination of a programmable unit and an integrated circuit (IC) dedicated to generate the checksum vaiue. In this embodiment the programmable unit may collect the dose-setting information, while the dose-displaying information may be collected by the IC which generates a checksum value and forwards the generated checksum value to the processor, which then relates the generated checksum value to the reference checksum value.

In the latter embodiment, the IC may be integrated into the display, whereby the display instead of outputting dose-setting information relating to each pixel of the display, outputs a checksum value generated on said information.

In one embodiment a reference checksum value is generated for each pattern/character/- number which the device is adapted to display e.g. the numbers from 0-9. When a dose is set and displayed, a checksum is generated for each character displayed. Thus, if a three digit value is displayed, three checksum values are generated. Determination of whether the displayed dose corresponds to the set dose is performed by comparing each of the generated checksum values with each of the reference checksum values. Thus for a three digit display, wherein each digit is adapted to display the numbers 0-9, the number of comparisons will be 3x10=30. An advantage of this embodiment is that the number of reference checksum values which need to be stored, is reduced. Alternatively, a reference checksum should be stored for any combination of the reference checksums, i.e. in the above three digit example 10³=1000 references checksum values should be stored.

The medical device may comprise a reservoir for accommodation of a medicament to be ejected. The reservoir may form an integral part of the device such that once removed, the device cannot operate anymore. As an alternative the reservoir may be adapted to be removed e.g. when used, and to be replaced by another reservoir such as a filled reservoir.

The input device may comprise a keyboard such as a numeric keyboard, for entering a dose to be ejected. Alternatively, the input device may take the form of a dose setting member the position (translationally and/or rotationally) of which, relative to the remaining part of the medical device, is indicative for the amount of the set dose. As an example the dose setting member may comprise a rotatable knob e.g. positioned at one end of the dose setting device. Moreover, the input device may comprise a sensor adapted to determine the position of a member such as a piston rod, which is adapted to move during dose setting and the position of which is indicative of the set dose. The input device may be electrically connected to the processor such that a signal outputted by the input device may be detected by the processor.

The processor may comprise a checksum list comprising a plurality of reference checksum values, such as the values from 0-9. Moreover, the processor may be programmed to relate the generated checksum value to at least one of the reference checksum values from the list so as to determine whether the generated checksum value corresponds to any of said reference checksum values. In one embodiment, the processor is adapted to halt the search for a reference checksum value upon identification of a matching reference checksum value. Thus, if the character "3" is displayed in the display and a search for a reference checksum corresponding to the character "3" is initiated, the search is halted upon identification of the checksum value corresponding to the character "3". If the processor is adapted to search in an ascending order 0,1,2,3, etc., the matching character is identified by the processor after comparison between the generated checksum value with four reference checksum values from the list, instead of relating the generated checksum value to all ten reference checksum values. Accordingly, processing time is reduced.

The reference checksum values may comprise any of the numbers 0-9, and/or any letter from a to z (majuscules and/or minuscule) including special national letters such as 33,ø, a and/or any special character such as #, *, ? etc. Furthermore, the reference checksum values may comprise graphical symbols such as bullets, parts of a pie chart etc.

In one embodiment the reference checksum value(s) are generated prior to use of the medical device and loaded into a memory of the device, e.g. in connection with manufacture of the memory and/or the device and/or the processor.

In one embodiment, each of the reference checksum values of the list corresponds to one predetermined symbol or one predetermined sequence of symbols displayable in the display. Moreover, the processor may be programmed to relate the generated checksum value to one or more of the reference checksum values of the list so as to identify a symbol or a sequence of symbols displayed in the display. As an example the processor may be adapted to determine whether a predetermined number is displayed in the display. In order to determine whether the displayed number corresponds to the set dose, the processor may be programmed to relate the displayed symbol to the dose-setting information so as to determine whether the displayed dose corresponds to the set dose.

In order to prevent injection of an incorrect dose, the medical device may be programmed to prevent ejection of a dose if the dose-displaying information differs from the dose-setting information. This prevents accidents wherein the user is lead to believe that a relatively small dose is injected when in fact a much larger dose (possible lethal) is injected.

For each character displayed, a unique checksum value is generated. Any errors in the display will result in checksum values which do not correspond to any of the reference checksum values, whereby the displayed dose cannot be identified. Accordingly, the processor may be programmed to identify any malfunction in any of a plurality of individually controllable pixels/segments for indication of the set dose. In one embodiment the processor is adapted to test each pixel upon start-up of the device, while in other embodiments the processor is adapted to test each pixel prior to each setting of a dose.

The checksum value may be generated by means of any known equations for generating checksum values. As an example the generated checksum value may be a cyclic redundancy checksum (CRC). The size of the checksum value should preferably be chosen such that its bit size is as small as possible. However, it must be ensured that the size is large enough to ensure that redundancy is avoided i.e. such that it is avoided that different characters yield the same checksum value.

In a SECOND aspect the present invention relates to a method of verifying a dose set on a medical device comprising: an input device adapted to determine a set dose and to output a signal comprising dose-setting information relating to the set dose; and a processor programmed to collect the dose-setting information and to display the set dose on a display, the processor being programmed to collect dose-displaying information from the display said dose-displaying information relating to the displayed dose, the processor being programmed to generate a checksum value on the basis of at least a part of the dose-displaying information and to relate the generated checksum value to a reference checksum value so as to determine whether the displayed dose corresponds to the set dose; the method comprising the steps of: - determining a set dose, displaying the set dose, retrieving dose displaying information from the display, generating a checksum value on the basis of at least a part of the dose displaying information, and relating the generated checksum value to one or more reference checksum value(s).

The step of determining the set dose may comprise the step of retrieving dose setting information from the input device. The dose setting information may be retrieved by forwarding a request for information from the processor to the input device, whereby the input device provides the requested information.

Moreover, the processor may comprise a checksum list comprising a plurality of reference checksum values and the step of relating may comprise the step of: relating the generated checksum value to at least one of the reference checksum values of the list so as to determine whether the generated checksum value corresponds to any of the reference checksum values.

Furthermore, each of the reference checksum values of the list may correspond to one predetermined symbol or one predetermined sequence of symbols displayable in the display. Additionally, the step of relating may comprise the step of: relating the generated checksum value to one or more of the reference checksum values of the list so as to identify a symbol or a sequence of symbols displayed in the display.

In one embodiment the step of relating further comprises the step of: relating the displayed symbol or sequence of symbols to the dose-setting information so as to determine whether the displayed dose corresponds to the set dose.

The step of generating a checksum may comprise the step of: generating a cyclic redundancy checksum (CRC).

Additionally, the method may further comprise the step of: requesting a user to acknowledge the displayed dose. Said step may comprise displaying a request on the display and determining activation of an accept button on the medical device. In embodiments wherein the input device comprises a keyboard, the accept button may be a specific character on the keyboard e.g. "Y" for yes, or a specific combination of characters pressed simultaneously or in a predetermined sequence. If the displayed dose is not acknowledged by the user, a further step in the method may be: preventing ejection of the set dose. The latter step may follow the step of requesting a user to acknowledge.

The invention according to the first aspect may comprise any feature or element of the invention according to the second aspect and vice versa.

DEETAILED DESCRIPTION OF THE INVENTION Fig. 1 discloses a display comprising two 7-segments,

Fig. 2 discloses a display comprising two integer-digit displays and one point-digit display, and

Fig. 3 discloses a display divided into three large display zones, and one small display zone.

Fig 1. discloses a display 100 comprising two 7-segments 102 each of which comprises 7 individually controllable segments 104a-g. In one embodiment the segments are each adapted to emit visible radiation while in other embodiments the segments are individually controllable liquid crystals which themselves do not emit visible radiation, but which are visible in natural or artificial light or when backlid. In order to determine whether the dose displayed by means of the display corresponds to the set dose, a processor associated with the display is programmed to retrieve dose-displaying information from the display.

The dose-displaying information comprises information relating to the activation or non- activation of each segment, and as indicated in the drawing this information requires 7 bit of information - one bit per segment - for each 7-segment 102. As this is approximately one byte (8 bit), a practical approach would be to determine the displayed number on a byte basis, i.e. one byte for each 7-segment.

When the determination of a number is performed on a byte basis, 10 comparisons are made in order to determine whether the displayed number is one of the numbers from 0-9.

Analogously, for a two digit 7-segment display as illustrated in Fig. 1, 20 comparisons are made in order to determine the displayed number. However, as most processors are capable of comparing words (2 bytes), such processors may determine the displayed number by making 10 word comparisons, see also the table below. With increasing resolution of displays, the task of determining the displayed dose increases. As shown in the table below the 224-pixel-element and the 520-pixel-element of Fig. 2, increases the pixel-by-pixel (segment-by-segment) comparison task considerably. A 224- pixel element corresponds to 14 words, and, thus, in order to determine any number in the range 0-9, 14x10=140 comparisons must be made. Similarly, a 520-pixel-element corresponds to 33,2 words, i.e. 33 words, and in order to determine any number in the range 0-9, 33x10=330 comparisons must be made.

According to the invention, this task is reduced by determining a checksum value whereby the task of determining a displayed dose is transformed into a task of generating a checksum value, and a task of comparing the generated checksum value with a reference checksum.

Table 1: Determination on a word-basis in a processor

The display of Fig. 2 comprises two integer-digits 202 and one point-digit 204. The integer- digits 202 are separated form the point digit 204 by a point 206. In the embodiment of Fig. 2 the point 206 is always activated and is thus not be subjected to the comparison. However, in other embodiments the point is also subjected to the verification of the displayed number.

A displayed number is determined by subjecting the three digits to the previously described comparison process. The size of the CRC-sum may be reduced if the size of the display segment is reduced accordingly.

Fig. 3 discloses an alternative to the display of Fig. 2, wherein the integer-digits202', the point-digit 204' and the point 206' are provided as zones of the same display instead of a plurality of segments. Accordingly, the processor is adapted to determine checksum values for predetermined zones of the display, i.e. oniy for parts of the display. In the embodiment of Fig. 3, the size of the integer-digit zones is identical to the size of the integer zones of Fig. 2.

In the embodiment of Fig. 3 the first integer-digit 202', instead of displaying the number "0" is not displaying any number. Accordingly, in such embodiments the device must comprise a reference checksum corresponding to a blank zone. It will be appreciated that such blank characters are not limited to displays where defining zones for each character, but may also be used in embodiments comprising a plurality of displays such as the one disclosed in Fig. 2.

Claims

1. A medical device for ejecting a dose of a medicament, the device comprising: an input device adapted to determine a set dose and to output a signal comprising dose- setting information relating to the set dose; and - a processor programmed to collect the dose-setting information and to display the set dose on a display, the processor being programmed to collect dose-displaying information from the display, said dose-displaying information relating to the displayed dose, the processor being programmed to generate a checksum value on the basis of at least a part of the dose-displaying information and to relate the generated checksum value to at least one reference checksum value so as to determine whether the displayed dose corresponds to the set dose.

2. A medical device according to claim 1, wherein the processor comprises a checksum list comprising a plurality of reference checksum values and wherein the processor is programmed to relate the generated checksum value to at least one of the reference checksum values of the list so as to determine whether the generated checksum value corresponds to any of the reference checksum values.

3. A medical device according to claim 2, wherein each of the reference checksum values of the list corresponds to one predetermined symbol or one predetermined sequence of symbols displayable in the display, and wherein the processor is programmed to relate the generated checksum value to one or more of the reference checksum values of the list so as to identify a symbol or a sequence of symbols displayed in the display.

4. A medical device according to claim 3, wherein the processor is programmed to relate the displayed symbol or sequence of symbols to the dose-setting information so as to determine whether the displayed dose corresponds to the set dose.

5. A medical device according to any of the preceding claims, wherein the medical device is programmed to prevent ejection of a dose if the dose-displaying information differs from the dose-setting information.

6. A medical device according to any of the preceding claims, wherein the processor is programmed to prevent ejection of a dose if the dose-displaying information has not been acknowledged by a user of the medical device.

7. A medical device according to any of the preceding claims, wherein the display comprises a plurality of individually controllable pixels/segments for indication of the set dose and wherein the processor is programmed to identify malfunction in any of the individually controllable pixels/segments.

8. A medical device according to any of the preceding claims, wherein the checksum value is a cyclic redundancy checksum (CRC).

9. A medical device according to any of the preceding claims, wherein the input device comprises a keyboard for entering a dose to be ejected.

10. A method of verifying a dose set on a medical device comprising: an input device adapted to determine a set dose and to output a signal comprising dose-setting information relating to the set dose; and a processor programmed to collect the dose-setting information and to display the set dose on a display, the processor being programmed to collect dose-displaying information from the display, said dose-displaying information relating to the displayed dose, the processor being programmed to generate a checksum value on the basis of at least a part of the dose-displaying information and to relate the generated checksum value to at least one reference checksum value so as to determine whether the displayed dose corresponds to the set dose, the method comprising the steps of: determining a set dose, displaying the set dose, retrieving dose displaying information from the display, - generating a checksum value on the basis of at least a part of the dose displaying information, and relating the generated checksum value to the at least one reference checksum value.

11. A method according to claim 10, wherein the processor comprises a checksum list comprising a plurality of reference checksum values and wherein the step of relating comprises the step of: relating the generated checksum value to at least one of the reference checksum values of the list so as to determine whether the generated checksum value corresponds to any of the reference checksum values.

12. A method according to claim 11, wherein each of the reference checksum values of the list corresponds to one predetermined symbol or one predetermined sequence of symbols displayable in the display, and wherein the step of relating comprises the step of: relating the generated checksum value to one or more of the reference checksum values of the list so as to identify a symbol or a sequence of symbols displayed in the display.

13. A method according to claim 12, wherein the step of relating further comprises the step of: relating the displayed symbol or sequence of symbols to the dose-setting information so as to determine whether the displayed dose corresponds to the set dose.

14. A method according to any of claims 10-13, further comprising the step of: requesting a user to acknowledge the displayed dose.

15. A method according to claim 14, further comprising the step of: preventing ejection of the set dose if the displayed dose has not been acknowledged by the user.

16. A method according to any of claims 10-15, wherein the step of determining the set dose comprises the step of: retrieving dose setting information from the input device.

17. A method according to any of claims 10-16, wherein the step of generating a checksum comprises the step of generating a cyclic redundancy checksum (CRC).