Method and System for Providing Continuous Calibration of Implantable Analyte Sensors
Method and system for providing continuous calibration of analyte sensors includes calibrating a first sensor, receiving data associated with detected analyte levels from the first sensor, and calibrating a second sensor based on a predetermined scaling factor and data associated with detected analyte levels from the first sensor, is disclosed.
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The present application is a continuation of U.S. patent application Ser. No. 13/022,620 filed Feb. 7, 2011, now U.S. Pat. No. 8,506,482, which is a continuation of U.S. patent application Ser. No. 11/365,340 filed Feb. 28, 2006, now U.S. Pat. No. 7,885,698, entitled “Method and System for Providing Continuous Calibration of Implantable Analyte Sensors”, the disclosure of which is incorporated herein by reference for all purposes.
BACKGROUNDContinuous monitoring of analytes of a patient generally uses an analyte sensor that that is at least partially implanted in the patient so as to be in fluid contact with the patient's analytes such as interstitial fluid or blood. The analyte sensor typically is replaced after a predetermined time period such as three, five or seven day period, when a new sensor is implanted in the patient to replace the old sensor. During the sensor replacement process, a gap or interruption in the analyte monitoring occurs. For example, during the time period in which the patient removes the implanted analyte sensor to replace with a new analyte sensor, the patient is unable to monitor or determine the analyte values such as glucose levels. In this manner, with continuous glucose monitoring systems presently available which use short term analyte sensors, there is always a gap in service during which data associated with the measurement of the patient's analyte levels cannot be obtained.
In addition, calibration of each implanted analyte sensor, which is necessary before data from the analyte sensor can be obtained, is laborious, time consuming, and error prone. Factory calibration is not a practical approach due to substantial sensor to sensor variability of signal strength introduced during the manufacturing process, and also, due to additional variability imposed by the sensors' response to the in-vivo environment which varies from patient to patient.
Thus, typically it is necessary to perform in-vivo calibration, in which the analyte sensor is calibrated, post implantation, by comparison with a reference blood glucose value. Generally these reference blood glucose values include capillary blood glucose values obtained by finger or arm stick using a conventional blood glucose meter. To perform the calibration using the reference blood glucose values, a substantial number of capillary values such as, for example, one to four capillary measurements daily, are necessary to ensure the continued calibration (and thus, accurate) values determined by the analyte sensors.
Moreover, calibrations may sometimes be inaccurate due to transient sensitivity changes which generally occur early in the lifetime of an implanted sensor, and sometimes referred to as early sensitivity attenuation, or ESA. If a calibration is assigned to an analyte sensor undergoing a transient change in sensitivity, inaccurate sensor readings or measurements will result at a later point in time, when the sensitivity reverts to its “true” value.
Further, the typical calibration process is performed for each newly implanted glucose sensor. More specifically, with the placement of each glucose sensor, a new set of blood capillary reference values are obtained, and which is the sole basis (or reference) for calibration of that particular sensor during the usage life of the sensor, for example, during a three, five or a seven day period.
In view of the foregoing, it would be desirable to have an approach to provide methods and system for continuous analyte monitoring where no gap in service can be achieved. In addition, it would be desirable to have methods and a system to verify the stability of a newly implanted sensor, before obtaining user-accessible analyte data from the sensor. Furthermore, it would be desirable to have methods and system for continuous analyte monitoring for continuous calibration of analyte sensors and which minimizes the number of necessary fingerstick (or armstick) calibrations of the analyte sensors using glucose meters, and also, to provide alternate reference.
SUMMARY OF THE INVENTIONIn view of the foregoing, in accordance with the various embodiments of the present invention, there is provided a method and system in which short term sensors may be calibrated based on the data associated with prior short term sensors by providing an overlap in the sensor placement during the sensor replacement process such that fewer, or in the limit, no additional capillary blood glucose values are needed for calibration of subsequent sensors, and further, analyte levels are continuously monitored without any interruption, for example, during the periodic sensor replacements in the continuous analyte monitoring system.
These and other objects, features and advantages of the present invention will become more fully apparent from the following detailed description of the embodiments, the appended claims and the accompanying drawings.
Referring to
In an alternate embodiment, each of the transmitters 121A and 121B may be individually coupled to a corresponding receiver section (for example, separate receiver/data processing sections of the receiver/data processing unit 130) such that each transmitter 121A and 121B are uniquely operatively coupled to the respective receiver/data processing units. In addition, each receiver/data processing unit may be configured to communicate with each other such that data from the transmitters 121A and 121B may be interchangeably communicated. Furthermore, while
Furthermore, in yet another embodiment of the present invention, the transmitter unit 121A and transmitter unit 121B may be physically coupled in a single housing so as to provide a single transmitter section for the patient, which is configured to support multiple transmitter units 121A, 121B. Moreover, while two transmitter units 121A, 121B are shown in
Moreover, referring to
The transmitter units 121A, 121B may, in one embodiment, be configured to transmit the analyte related data substantially in real time to the receiver/data processing unit 130 after receiving it from the corresponding analyte sensors 111A, 111B respectively. For example, the transmitter units 121A, 121B may be configured to transmit once per minute to the receiver/data processing unit 130 based on analyte levels detected by the corresponding analyte sensors 111A, 111B respectively. While once per minute data transmission is described herein, within the scope of the present invention, the transmitter units 121A, 121B may be configured to transmit analyte related data more frequently (such as, for example, once every 30 seconds), or less frequently (for example, once every 3 minutes).
Additional analytes that may be monitored, determined or detected by analyte sensors 111A, 111B include, for example, acetyl choline, amylase, bilirubin, cholesterol, chorionic gonadotropin, creatine kinase (e.g., CK-MB), creatine, DNA, fructosamine, glucose, glutamine, growth hormones, hormones, ketones, lactate, peroxide, prostate-specific antigen, prothrombin, RNA, thyroid stimulating hormone, and troponin. The concentration of drugs, such as, for example, antibiotics (e.g., gentamicin, vancomycin, and the like), digitoxin, digoxin, drugs of abuse, theophylline, and warfarin, may also be determined.
Moreover, within the scope of the present invention, transmitter units 121A, 121B may be configured to directly communicate with one or more of the remote terminal 140 or the delivery unit 150, and in addition, the receiver/data processing unit 130 may be integrated with one or more of the remote terminal 140 or the delivery unit 150. Furthermore, within the scope of the present invention, additional devices may be provided for communication in the continuous analyte monitoring system 100 including additional receiver/data processing unit, remote terminals (such as a physician's terminal) and/or a bedside terminal in a hospital environment, for example.
In accordance with the various embodiments of the present invention, the analyte sensors 111A, 111B may be inserted through the skin of the patient using insertion devices having a predefined or configured insertion mechanism (spring loaded devices, for example) which facilitates the placement and positioning of the analyte sensors through the patient's skin, and so as to be in fluid contact with the patient's analytes. Alternatively, the sensors 111A, 111B may be manually deployed using an insertion guide or needle.
As described in further detail below, the continuous calibration process in one embodiment includes deploying and calibrating a first sensor (e.g., analyte sensor 111A) at predetermined time intervals using finger stick calibrations, for example, at 10 hours, 12 hours, 24 hours and 72 hours from the initial insertion of the first sensor 111A. Moreover, the first and subsequent analyte measurements may be obtained after the initial calibration at 10 hours when the analyte sensor has substantially reached a stability point. Thereafter, prior to the termination of the first sensor life (for example, at the 120th hour for a 5 day sensor), a second analyte sensor (for example, sensor 111B) is inserted into the patient and during the period of overlap of the first and second analyte sensors 111A, 111B, the second analyte sensor 111B is correlated with the first analyte sensor 111A values and the second analyte sensor 111B is calibrated in reference to the first analyte sensor 111A values such that the second analyte sensor 111B and any additional subsequent analyte sensors do not require the multiple (or preferably, any) fingerstick calibrations as is the case for the first analyte sensor 111A.
In this manner, the short term analyte sensors are overlapped for a predetermined time period to allow the output of the first and second sensors to be correlated to detect potential transient sensitivity (e.g., ESA) in the second sensor. The detection of potential transient sensitivity in the second sensor can be achieved with substantial accuracy since the first sensor has had a substantial time period (e.g., several days of usage) to stabilize. Upon establishing an acceptable level of correlation, the calibration of the first sensor in one embodiment is assigned or transferred to the second sensor. More specifically, in one embodiment, the continuous data from a previously calibrated first sensor is used as a set of reference values to calibrate the second newly implanted sensor.
In this manner, in one embodiment of the present invention, a substantially accurate calibration may be assigned to the second sensor while using no additional capillary blood glucose values for calibration, and further, this approach of correlation and transfer calibration may be repeated for subsequent sensors in the continuous monitoring system 100 such that analyte levels are continuously monitored without any interruption, for example, during the periodic sensor replacements in the continuous analyte monitoring system 100.
More specifically, the transmitter unit 121A (
Referring to
Referring again to
In the manner described above, in one embodiment of the present invention, there is provided a system and method of continuously calibrating implanted analyte sensors that provide accurate detection of initial instabilities of the implanted sensors, reduce the number of required blood capillary tests for calibration, increase the calibration accuracy, and also, eliminate any gaps or interruptions in the continuous analyte data or record monitored by the continuous monitoring system 100.
Moreover, in a further embodiment, the receiver/data processing unit 130 may be configured to prompt the patient for confirmation and also, for the sensor calibration code when the receiver/data processing unit 130 detects data or signals received from the transmitter unit 121B coupled to the second sensor 111B.
Thereafter, at step 320, the receiver/data processing unit 130 is configured to determine a scaling factor for the second sensor 111B based on the data or signals from the first sensor 111A. More specifically, in one embodiment, the receiver/data processing unit 130 is configured to perform a predefined autocorrelation function to determine the scaling factor for the second sensor 111B. Alternatively, in another embodiment, the data from the second sensor 111B is multiplied by a range of predetermined initial scaling factors to determine an average error between the data from the first sensor 111A and the data from the second sensor 111B. Based on the calculated average error, the scaling factor is determined as the one of the predetermined initial scaling factors which yield the smallest possible calculated average error.
In a further embodiment, the scaling factor may be determined by calculating an average of the ratio of the two raw signals from the first sensor 111A and the second sensor 111B, or any other suitable manner in which to determine a suitable scaling factor.
Referring to
In other words, referring back to
In other words, once it is determined that the second sensor 111B is stable, then a sensitivity may be determined for the second sensor 111B based on the scaling factor determined at step 320 and the sensitivity of the first sensor 111A. This determination may be expressed as follows:
S2=S1*Σ(I2/I1) (1)
where S2 represents the sensitivity of the second sensor 111B, S1 represents the sensitivity of the first sensor 111A, and Σ(I2/I1) represents the scaling factor which correlates the data of the first sensor 111A and the second sensor 111B.
In this manner, once the second sensor 111B is calibrated, the accuracy of data from the second sensor 111B is substantially similar to the accuracy of the data from the first sensor 111A, where the calibration of the second sensor 111B was performed without any capillary blood glucose measurements by, for example, fingerstick testing using glucose meters. By way of an example, based on a first sensor sensitivity S1 at 0.686 nA/mM, and with a scaling factor Σ(I2/I1) of 0.725, the sensitivity S2 of the second sensor 111B is determined to be 0.497 nA/mM.
In the manner described above, in one embodiment of the present invention, there is provided a system and method of continuously calibrating implanted analyte sensors that provide accurate detection of initial instabilities of the implanted sensors, reduce the number of required blood capillary tests for calibration, increase the calibration accuracy, and also, eliminate any gaps or interruptions in the continuous analyte data or record monitored by the continuous monitoring system 100.
Moreover, in accordance with the present invention, using the data correlation during the time period when the sensors overlap in time, the calibration frequency may be reduced while increasing the calibration accuracy. Moreover, additional calibration information may also be obtained from the sensor calibration codes predetermined and assigned during sensor manufacturing, and which may be used to improve calibration accuracy without requiring additional or increased capillary blood glucose testing.
Accordingly, a method of providing continuous calibration of analyte sensors in one embodiment of the present invention includes calibrating a first sensor, receiving data associated with detected analyte levels from the first sensor, and calibrating a second sensor with reference to one or more detected analyte levels from the first sensor.
The method in one embodiment may further include a step of calibrating a third sensor based on a second scaling factor and data associated with detected analyte levels from the second sensor. Moreover, the step of calibrating the second sensor may in one embodiment, start after a predetermined time period has passed where the first sensor has been in fluid contact with an analyte of a patient, where the predetermined time period may include at least approximately 90% or alternatively, 50% of the life of the first sensor.
In yet another embodiment, the method may further include the step of determining a sensitivity of the first sensor.
In another aspect, the method may also include the step of receiving data associated with detected analyte levels from the second sensor.
In accordance with still another embodiment, the step of calibrating the second sensor may include the steps of determining an analyte level, and comparing the determined analyte level with the data associated with the detected analyte level from the first sensor.
The step of calibrating the second sensor in yet another embodiment may include the steps of determining a scaling factor based on substantially simultaneous data from the first sensor and the second sensor, applying the scaling factor to the data from the second sensor, determining a correlation level of data from the first sensor and from the second sensor.
In another aspect, the step of determining the scaling factor may include the steps of comparing the substantially simultaneous data from the first sensor with the data from the second sensor, and determining the scaling factor based on a calculated scaling factor with the lowest level of average error between the data of the first sensor and the data of the second sensor.
The method in yet another embodiment may include the step of comparing the correlation level with a predetermined correlation threshold defining an acceptable stability level of the second sensor.
The first sensor and the second sensor may be analyte sensors.
This may further include the step of removing the first sensor while retaining the second sensor in fluid contact with the analyte of a patient.
In addition, the first sensor and the second sensor may be subcutaneously positioned under a skin of a patient, where at least a portion of the first sensor and at least a portion of the second sensor are in fluid contact with the patient's analyte.
A system for providing continuous analyte sensor calibration in accordance with another embodiment of the present invention includes a first sensor for subcutaneous placement in a patient, a second sensor for subcutaneous placement in the patient after calibration of the first sensor, where at least a portion of the first sensor and at least a portion of the second sensor are in fluid contact with the patient's analyte substantially simultaneously for a time period.
In one aspect, the time period may be predetermined and includes approximately 2 hours to 10 hours.
Alternatively, in another aspect, the time period may be variable, and where the variable time period may be determined to be when the analyte levels measured by the first and second sensors are within a correlation range, the correlation range being determined by a preset threshold value.
The second sensor may subcutaneously placed in the patient after a predetermined time period has passed where the first sensor has been in fluid contact with an analyte of a patient, and where the predetermined time period includes at least approximately 90% or 50% of the life of the first sensor.
In a further embodiment, the first sensor may be operatively coupled to a first transmitter unit, and the second sensor is operatively coupled to a second transmitter unit, the first and second transmitter units configured to receive data from the corresponding first and second sensors, respectively, for transmission over a communication link.
The first transmitter unit and the second transmitter unit may be coupled to a single transmitter housing.
The communication link may include one or more of an RF communication link, a Bluetooth® communication link, an infrared communication link, or a cable communication link.
The system in another embodiment may include a receiver unit configured to substantially simultaneously receive data from the first transmitter unit and the second transmitter unit.
The receiver unit may include a first receiver section operatively coupled to the first transmitter unit, and a second receiver section operatively coupled to the second transmitter unit, the second receiver section further operatively coupled to the first receiver section for data communication.
The receiver unit may also include an infusion device.
The receiver unit may be configured to calibrate the second sensor based on analyte levels measured by the first sensor.
The receiver unit may be configured to receive data from one or more of the first sensor or the second sensor at predetermined time intervals such that there is no interruption in the received data after the first sensor is removed from the patient.
A method in another embodiment of the present invention may include positioning a first sensor in fluid contact with an analyte of a patient, calibrating the first sensor, positioning a second sensor in fluid contact with the analyte of the patient after calibrating the first sensor, calibrating the second sensor based on data from the first sensor, and removing the first sensor while retaining the second sensor in fluid contact.
The second sensor in one embodiment may be subcutaneously placed in the patient after a predetermined time period has passed where the first sensor has been in fluid contact with an analyte of a patient.
In one embodiment, the stability of the second sensor may be verified by correlation of its output with the output of the stabilized first sensor, prior to calibration of the second sensor based on data from the first sensor, and thereafter removing the first sensor while retaining the second sensor in fluid contact.
A system for determining the stability of an analyte sensor calibration in accordance with still yet another embodiment includes a first sensor for subcutaneous placement in a patient, and a second sensor for subcutaneous placement in the patient after calibration of the first sensor, where at least a portion of the first sensor and at least a portion of the second sensor are in fluid contact with the patient's analyte substantially simultaneously for a time period, and further, where the stability of the second sensor is determined with reference to data from the first sensor.
The time period may be predetermined and includes approximately 2 hours to 10 hours.
Alternatively, the time period may be variable, and where the variable time period may be determined to be when the analyte levels measured by the first and second sensors are within a correlation range which may be determined by a preset threshold value.
A system for determining analyte concentrations in yet another embodiment includes a plurality of analyte sensors, a plurality of transmitter units, each of the plurality of transmitter units operatively coupled to a respective one of the plurality of analyte sensors, a single receiver unit configured to receive and process data substantially simultaneously from all of the plurality of transmitter units, where each transmitter is uniquely couple to a single analyte sensor.
The receiver unit may also include a comparison unit for comparing the one or more signals from the plurality of transmitters units, and also for determining the stability of the plurality of sensors. In addition, the receiver unit may be further configured to determine the calibration of the plurality of sensors based on the comparison unit.
Various other modifications and alterations in the structure and method of operation of this invention will be apparent to those skilled in the art without departing from the scope and spirit of the invention. Although the invention has been described in connection with specific preferred embodiments, it should be understood that the invention as claimed should not be unduly limited to such specific embodiments. It is intended that the following claims define the scope of the present invention and that structures and methods within the scope of these claims and their equivalents be covered thereby.
Claims
1. A method of providing analyte sensor calibration, comprising the steps of:
- receiving data associated with monitored analyte level from a first analyte sensor in fluid contact with interstitial fluid under a skin surface;
- receiving data associated with monitored analyte level from a second analyte sensor in fluid contact with the interstitial fluid under the skin surface;
- comparing the received data from the first analyte sensor with the received data from the second analyte sensor;
- determining a scaling factor based on the comparison and an initial scaling factor;
- applying the determined scaling factor to the received data from the second analyte sensor; and
- determining a correlation level of signals from the first analyte sensor and the signals from the second analyte sensor.
2. The method of claim 1 further including calibrating the second analyte sensor based on the received data from the first analyte sensor.
3. The method of claim 1 wherein the scaling factor is based on a predetermined level of average error between the data of the first analyte sensor and the data of the second analyte sensor.
4. The method of claim 1 further including initiating the calibration of the second analyte sensor after a predetermined time period has elapsed since the first analyte sensor is maintained in fluid contact with the interstitial fluid.
5. The method of claim 4 wherein the predetermined time period includes approximately 90% of the life of the first analyte sensor.
6. The method of claim 4 wherein the predetermined time period includes approximately 50% of the life of the first analyte sensor.
7. The method of claim 1 further including determining a sensitivity associated with the first analyte sensor.
8. The method of claim 1 wherein calibrating the second analyte sensor includes determining an analyte level and comparing the determined analyte level with the data associated with the detected analyte level from the first analyte sensor.
9. The method of claim 1 further including comparing the correlation level with a predetermined correlation threshold.
10. The method of claim 9 wherein the predetermined correlation threshold defines an acceptable stability level of the second analyte sensor.
11. The method of claim 10 wherein when the correlation level is above the predetermined correlation threshold, confirming that the second analyte sensor is stable.
12. The method of claim 10 wherein when the correlation level is above the predetermined correlation level, calibrating the second analyte sensor based on one or more detected analyte levels from the first analyte sensor.
13. The method of claim 12 wherein calibrating the second analyte sensor includes transferring one or more calibration parameters associated with calibration of the first analyte sensor to the calibration of the second analyte sensor.
14. The method of claim 10 wherein when the correlation level is below the predetermined correlation threshold, determining again the correlation level of the signals from the first analyte sensor and the signals from the second analyte sensor.
15. The method of claim 1 wherein the scaling factor is determined based on an average of the ratio of the signals from the first analyte sensor and the second analyte sensor.
16. The method of claim 1 wherein a predetermined level of average error between the data of the first analyte sensor and the second analyte sensor includes a lowest level of average error.
17. The method of claim 1 further including outputting information associated with the monitored analyte level by one or more of the first analyte sensor and the second analyte sensor.
18. The method of claim 1 further including performing initial calibration of the first analyte sensor based on a reference measurement.
19. The method of claim 18 wherein the reference measurement is obtained before the first analyte sensor is in fluid contact with the interstitial fluid.
20. The method of claim 1 wherein the second analyte sensor is calibrated in real time when the second analyte sensor is positioned in fluid contact with the interstitial fluid under the skin layer.
Type: Application
Filed: Aug 5, 2013
Publication Date: Nov 28, 2013
Applicant: Abbott Diabetes Care Inc. (Alameda, CA)
Inventor: Benjamin Jay Feldman (Berkeley, CA)
Application Number: 13/959,302
International Classification: A61B 5/1495 (20060101);