Abstract:
A calibration system is disclosed for calibrating a first physiological monitoring device using a second physiological monitoring device. The first physiological monitor measures a first indication of a physiological parameter. The second physiological monitor measures a second indication of the physiological parameter. The first and second indications are used to calibrate the first physiological monitoring device.

Description:
PRIORITY CLAIM TO RELATED PROVISIONAL APPLICATIONS 
     The present application claims priority benefit under 35 U.S.C. § 119(e) to U.S. Provisional Patent Application Ser. No. 60/800,512, filed May 15, 2006, entitled “SYSTEMS AND METHODS FOR CALIBRATING MINIMALLY INVASIVE AND NON-INVASIVE PHYSIOLOGICAL SENSOR DEVICES.” The present application incorporates the foregoing disclosures herein by reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to the field of patient monitor calibration. More specifically, the present invention relates to using a first physiological monitor to calibrate a second physiological monitor. 
     BACKGROUND 
     Diabetes is a common cause of kidney disease, blindness among adults under the age of 65, and limb amputation. The effects of diabetes can be greatly reduced, if not eliminated all together, with proper monitoring of blood glucose. Many glucose monitors in use today require that a person be pricked with a sharp object in order to draw a small amount of blood to test for glucose levels. This process of measuring blood is often painful and uncomfortable. Although minimally and non-invasive blood glucose systems are being developed, they generally suffer from signal processing challenges affecting accuracy. One common challenge of minimally invasive glucose monitoring systems is referred to as drift. Drift generally occurs during the first few hours or days that a minimally invasive monitor&#39;s probe is inserted in the body and may cause inaccuracies. 
     SUMMARY 
     Aspects of the present disclosure include systems and methods for calibrating minimally invasive and non-invasive physiological sensor devices. The calibration is used to improve accuracy. In some embodiments, when the system begins taking measurements, the system may experience drift.  FIG. 1  illustrates a graph  100  of glucose levels  101  in a patient vs. measured glucose  103  measured by a minimally invasive glucose monitor affected by drift. As illustrated, for a period of time, referred to herein as the calibration period, the measured glucose is less accurate due to, for example, drift. In minimally invasive systems, drift may be caused by protein buildup on the implanted device. In other systems, drift or other inaccuracies may be caused by any number of other issues known to an artisan from the disclosure herein. As with all patient monitors, more accurate and more reliable systems are preferred. 
     In an embodiment, a minimally invasive glucose monitor is described. The minimally invasive glucose monitor includes a probe which is inserted into a patient. The probe nearly continuously measures the patient&#39;s glucose levels and reports glucose information to the minimally invasive glucose monitor. The minimally invasive glucose monitor also includes a calibration input for receiving glucose information about the patient derived from a reliable glucose monitor. The glucose information received from the reliable glucose monitor is used to calibrate the minimally invasive glucose monitor. The minimally invasive glucose monitor may also include one or more outputs for outputting glucose and calibration related information. The inputs and outputs can be wired or wireless. 
     Although described with respect to glucose monitoring, a person of skill in the art will recognize that the present calibration system can be used to monitor and calibrate other physiological parameters, such as, for example, blood oxygen levels, blood carbon monoxide levels, blood pH levels, methemoglobin levels, pulse rates, trend or physiological traces, or any other physiological parameter. In addition, although described with respect to a minimally invasive patient monitor, the present disclosure is also applicable to the calibration of both invasive and non-invasive patient monitors. 
     In an embodiment, a method of calibrating a glucose measurement device is disclosed. The method includes acquiring a first indication of a glucose measurement from a first device, acquiring a second indication of a glucose measurement from a second device, and calibrating the second device using the first indication from the first device and the second indication from the second device. In an embodiment, the first and second devices comprise patient monitors. In an embodiment, the first and second devices are operably connected to the same patient. In an embodiment, the first and second indications are obtained at substantially the same time. In an embodiment, calibration comprises one or more of modeling, scaling, transforming, finding a best fit, finding a linear fit, filtering, adaptive correlation, and cross correlation. In an embodiment, the first device comprises an invasive physiological measurement device. In an embodiment, the second device comprises a minimally invasive physiological measurement device. In an embodiment, the second device comprises a non invasive physiological measurement device. 
     In an embodiment, a method of calibrating a physiological measurement device is disclosed. The method includes acquiring a first indication of one or more physiological measurements from a first device, acquiring a second indication of the one or more physiological measurements from a second device, and calibrating the second device using the first indication from the first device and the second indication from the second device. In an embodiment, the first and second devices comprise patient monitors. In an embodiment, the first and second devices are operably connected to the same patient. In an embodiment, the first and second indications are obtained at substantially the same time. In an embodiment, calibration comprises one or more of modeling, scaling, transforming, finding a best fit, finding a linear fit, filtering, adaptive correlation, and cross correlation. In an embodiment, the one or more physiological parameters comprise one or more of glucose, blood oxygen, pH, blood carbon monoxide levels, and methemoglobin. In an embodiment, the first device comprises an invasive physiological measurement device. In an embodiment, the second device comprises a minimally invasive physiological measurement device. In an embodiment, the second device comprises a non invasive physiological measurement device. 
     In an embodiment, a calibration system for calibrating a physiological measurement monitor is disclosed. The calibration system includes a first physiological monitor, a calibration module including a first input for inputting measured physiological data and a second input for inputting reliable data indicative of one or more physiological parameters. The calibration module is configured to calibrate the first physiological monitor using the information inputted over the first and second inputs. In an embodiment, the calibration system also includes a second physiological monitor for measuring the reliable data indicative of one or more physiological parameters. In an embodiment, the second physiological monitor comprises an invasive physiological measurement device. In an embodiment, the first physiological monitor comprises a minimally invasive physiological measurement device. In an embodiment, the first physiological monitor comprises a non invasive physiological measurement device. In an embodiment, the calibration system also includes one or more signal outputs. In an embodiment, the one or more signal outputs comprise a display output. In an embodiment, the one or more signal outputs comprise a trend output. In an embodiment, the one or more signal outputs comprise a waveform output. In an embodiment, the waveform output comprises a synthesized waveform. In an embodiment, the waveform output comprises a scaled waveform. In an embodiment, the one or more signal outputs comprise an error output. 
     In an embodiment, a method of calibrating a physiological measurement device is disclosed. The method of calibrating a physiological measurement includes acquiring a first indication of a glucose measurement from a first device, acquiring a second indication of a glucose measurement from a second device, and comparing the first indication and the second indication. Based on the comparison of the first indication and the second indication, if the first and second indications are not the same or close, the method also includes calibrating the second device using the first indication from the first device and the second indication from the second device, waiting an amount of time and requiring the first and second indications, comparing the reacquired first and second indications, and based on the comparison of the reacquired first and second indications, recalibrating the second device using the reacquired first and second indications. 
     In an embodiment, the amount of time comprises a predetermined amount of time. In an embodiment, the amount of time comprises about 5 minutes or less to about 12 hours or more. In an embodiment, the predetermined amount of time comprises about 5 minutes to about 10 minutes. In an embodiment, the predetermined amount of time comprises about 1 hour to about 2 hours. In an embodiment, the method also includes dynamically determining the amount of time. In an embodiment, dynamically determining comprises determining an amount of time based on the comparison of the first and second indications. In an embodiment, dynamically determining comprises determining an amount of time based on the comparison of the reacquired first and second indications. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The drawings and the associated descriptions are provided to illustrate embodiments of the disclosure and not to limit the scope of the claims. 
         FIG. 1  illustrates a graph of actual glucose v. measured glucose for a glucose monitor experiencing drift. 
         FIG. 2  illustrates a calibration system. 
         FIG. 3  illustrates a minimally invasive glucose monitor. 
         FIG. 4  illustrates a glucose calibration system. 
         FIG. 4A  illustrates another embodiment of a glucose calibration system. 
         FIG. 4B  illustrates yet another embodiment of a glucose calibration system. 
         FIG. 5  illustrates a flow chart of an embodiment of a calibration system. 
         FIG. 6  illustrates a flow chart of another embodiment of a calibration system. 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments of the present disclosure include systems and methods for calibrating a physiological monitoring device. A reliable, often invasive, method of measuring a physiological parameter is used to calibrate measurements of a minimally invasive or non-invasive physiological measurement device. In an embodiment, the reliable monitor and the minimally invasive or non-invasive monitor measure the same physiological parameter from the same patient within a time period deemed appropriate. In an embodiment, a patient can be set up with a long term, minimally invasive physiological measurement device with minimized discomfort during the initialization period. In an embodiment, a patient can use a minimally invasive physiological measurement device to continuously measure a physiological parameter, using an invasive measurement device periodically to calibrate the minimally invasive physiological measurement device. In an embodiment, the physiological parameter is one or more of glucose, blood oxygen, pH, blood carbon monoxide levels, and methemoglobin. 
       FIG. 2  illustrates a calibration system  200 . The calibration system includes a parameter calculator  201 . The parameter calculator includes one or more inputs  203  for reliable data indicative of one or more parameters and one or more inputs  205  for measurement data. The reliable data indicative of one or more parameters is communicated from a reliable, often invasive, patient monitor. The measurement data is communicated from a physiological sensor. 
     The parameter calculator  201  uses the reliable data indicative of one or more parameters to calibrate, if necessary, the measurement data or information derived from the measurement data. Calibration may include modeling, scaling, transforming, finding a best fit, finding a linear fit, filtering, adaptive correlation, cross correlation, or any other calibration steps known to a skilled artisan from the disclosure herein. 
     The parameter calculator  201  can calculate one or more physiological parameters and output information indicative of that parameter. The parameter calculator  201  may also advantageously calculate trend data and synthesize or scale waveform data. The parameter calculator  201  includes one or more outputs, such as, for example, parameter data output  207 , trend data output  209 , synthesized, scaled, or actual waveform output  211 , or calibration data output  213 . The parameter data output  207  communicates data indicative of one or more physiological measurements. The trend data output  209  communicates data indicative of trend information for the one or more physiological measurements. The synthesized, scaled, or actual waveform data output  211  communications waveform data which has been synthesized, scaled, or unaltered. The calibration data output  213  communicates information related to calibrations performed by the parameter calculator  201 . The outputs  207 ,  209 ,  211 ,  213  can communicate with display  215 , a separate patient monitoring device, or other device configured to receiving physiological parameter information. 
     In an embodiment, the parameter calculator  201  is included within a single device. In an embodiment, the parameter calculator  201  is included within several separate devices. In an embodiment, the parameter calculator  201  comprises a processor, processor board, or OEM board. In an embodiment, the parameter calculator  201  is portable. In an embodiment, the parameter calculator  201  comprises a desktop parameter calculator. Data communicated between the various components of the calibration system can be communicated through cables or wirelessly. A skilled artisan will also understand from the disclosure herein, that other inputs and/or outputs can be included with the system of the present disclosure. For example, an error data output can be used to communicate the error calculated between the measured data and the reliable data. 
       FIG. 3  illustrates an embodiment of a minimally invasive glucose monitor. As illustrated, a minimally invasive glucose monitor  301  is attached to a patient  300 . The minimally invasive glucose monitor  301  includes a probe  303  which is inserted into the body, often just beneath the skin. The probe  303  measures glucose levels in the patient  300 . The probe  303  communicates the measurements to the minimally invasive glucose monitor  301 . In an embodiment, the probe  303  is attached to the monitor  301 . In an embodiment, the probe is separate from the monitor  301 . In an embodiment, the probe  303  communicates through a cable connection with the monitor  301 . In an embodiment, the probe  303  communicates wirelessly with monitor  301 . In an embodiment, the monitor  301  is attached to the patient  300  by attachment piece  309 . In an embodiment, the monitor  301  includes a display  305 . In an embodiment, the monitor includes one or more buttons  307 . 
     In operation, the minimally invasive glucose monitor  301  continuously, nearly continuously, or intermittently (periodically or otherwise) measures blood glucose using probe  303 . The probe detects glucose levels present in the body and communicates the glucose levels to the minimally invasive glucose monitor  301 . The minimally invasive glucose monitor  301  calculates the patients glucose level based upon information acquired from probe  105 . Examples of a minimally invasive glucose monitor and probe are described in U.S. Pat. No. 6,613,379, entitled “Implantable Analyte Sensor,” issued to Ward et al., and U.S. Pat. No. 6,695,860, entitled “Transcutaneous Sensor Insertion Device,” also issued to Ward et al, the entire contents of both of which are herein incorporated by reference. 
       FIG. 4  illustrates an embodiment of a glucose calibration system. For example, the glucose level of a patient  300  is measured by a minimally invasive glucose monitor  301 . As described above, the minimally invasive glucose monitor  301  includes a probe  303  inserted into the patient  300  for measuring glucose levels. The glucose level of patient  300  is also measured by a reliable glucose monitor  401 . The reliable glucose monitor  401  communicates data indicative of glucose levels in patient  300  to the minimally invasive glucose monitor  201 . The minimally invasive glucose monitor  301  uses the communicated reliable data indicative of glucose levels in patient  300  to calibrate glucose information communicated by probe  303 . 
     In an embodiment, the reliable glucose monitor  401  communicates with the minimally invasive glucose monitor  301  through a cable or a wireless connection. In an embodiment, the reliable glucose monitor  401  and the minimally invasive glucose monitor  301  communicate with a separate calibration unit either through a cable or wirelessly. In an embodiment, the minimally invasive glucose monitor  301  communicates with the reliable glucose monitor  401 . In an embodiment, the minimally invasive glucose monitor  301  communicates a command to take a measurement to the reliable glucose monitor  401 . 
     In an embodiment, the reliable glucose monitor  401  is operably connected to an IV line  409 . The IV line  409  is operably connected to a catheter  411  which is inserted into a vein of the patient  300 . The reliable glucose monitor  401  is also operably connected to an IV line  405  which is operably connected to an fluid bag  407 . In operation, the reliable glucose monitor  401  intermittently draws blood from patient  300  through catheter  411  and IV line  409  and tests the blood for glucose levels. When the reliable glucose monitor  401  is not drawing blood from the patient  300 , it supplies fluid to the patient  300  from fluid bag  407  and IV line  405  through IV line  409  and catheter  411 . In an embodiment, the reliable glucose monitor  401  uses glucose test strips to measure glucose levels in the blood. In an embodiment, the reliable glucose monitor  401  uses chemicals analyses to test the glucose levels. 
     In an embodiment, the reliable glucose monitor  401  is programmed to take measurements at predetermined intervals. In an embodiment, the measurements are taken in intervals of about 5 minutes to about 12 hours. In an embodiment, the measurements are taken in intervals of about 5 minutes to about 10 minutes. In an embodiment, the measurements are taken in intervals of about 1 to about 2 hours. In an embodiment, the measurement intervals are dynamically determined based on calibration feedback as described below. In an embodiment, the minimally invasive glucose monitor  301 , or another intermediary device communicate a take measurement command to the reliable glucose monitor. In an embodiment, the minimally invasive or intermediary device communicate a take measurement command in predetermined or dynamically determined intervals as described above. 
       FIG. 4A  illustrates another embodiment of a glucose calibration system in which glucose test strips and a glucose test meter are used to measure glucose levels. A user uses the glucose test strips and glucose test meter to measure glucose levels. Once measured, the glucose test meter communicates the glucose levels to the minimally invasive glucose meter for calibration. 
       FIG. 4B  illustrates yet another embodiment of a glucose calibration system. In this embodiment, a glucose test meter is incorporated into the minimally invasive glucose monitor. A user uses the glucose test strips in conjunction with the minimally invasive glucose monitor to calibrate the minimally invasive glucose measurements. In an embodiment, the minimally invasive glucose monitor alerts a user that a reliable glucose measurement should be taken for calibration purposes. 
       FIG. 5  illustrates a flow chart of an embodiment of a calibration system. The system begins by nearly continuously acquiring minimally invasive glucose measurements at block  501 . The system then moves on to block  503  where the system acquires reliable glucose data. The system then moves on to block  505 , where a calibration module compares the invasive blood glucose measurement to the acquired minimally invasive glucose measurement. 
     Once the measurements are compared, the system moves on to decision block  507 , where the system looks to see if the measurements are the same or similar. Similar being defined herein as within a predetermined threshold. If the acquired minimally invasive measurement is the same or similar to the acquired reliable glucose data, then the system moves on to block  511  where the glucose reading is outputted, either to a display, a patient monitor, or to another device. If the minimally invasive measurement is not similar, or within a predetermined threshold, then the system moves on to block  509  where the minimally invasive measurements are calibrated. Once calibration is complete, the system moves on to block  511  where the glucose reading is outputted. The system then moves to block  513 , where the system decides whether or not the calibration period is complete. If the calibration period is not complete, the system moves to block  515  where it waits a predetermined period of time. After the period of time is complete, the system returns to block  503  and repeats the calibration process. If at block  513 , the calibration period is completed, then the system moves to block  517  where the system communicates a calibration complete signal. 
     In an embodiment, the determination of whether the calibration period is complete is based on an averaging of calibration periods required by other minimally invasive monitors. In an embodiment, the determination of whether the calibration period is compete is based on one or more comparisons of the reliable data and the minimally invasive measurement information. In one embodiment, the determination of whether the calibration period is complete is based on an averaging of calibration periods required by other minimally invasive monitors and one or more comparisons of the reliable data and the minimally invasive measurement information. 
       FIG. 6  illustrates a flow chart of another embodiment of a calibration system. The system begins by nearly continuously acquiring minimally invasive glucose measurements at block  601 . The system then moves on to block  603  where the system acquires reliable glucose data. The system then moves on to block  605 , where a calibration module compares the invasive blood glucose measurement to the acquired minimally invasive glucose measurement. 
     Once the measurements are compared, the system moves on to decision block  607 , where the system looks to see if the measurements are similar. If the acquired minimally invasive measurement is the same or similar to the acquired reliable glucose data, then the system moves on to block  611  where the predetermined wait period of block  617  is recalculated. The recalculation can be based on the number of accurate readings made by the minimally invasive device and/or the accuracy level of the readings made by the minimally invasive device and/or any other parameter which is useful for determining the duration between calibration cycles. The system then moves on to block  613  where the glucose readings are outputted. 
     If the minimally invasive measurement is not similar, or within a predetermined threshold, then the system moves on to block  609  where the minimally invasive measurements are calibrated. The system then moves on to block  613  where the glucose readings are outputted. Once calibration is complete, the system moves on to block  615 , where the system decides whether or not the calibration period is complete. If the calibration period is not complete, the system moves to block  617  where it waits the predetermined period of time, either as initially set or as dynamically recalculated at block  611 . After the period of time is complete, the system returns to block  503  and repeats the calibration process. If at block  615 , the calibration period is completed, then the system moves to block  619  where the system communicates a calibration complete signal. 
     Although the foregoing invention has been described in terms of certain preferred embodiments, other embodiments will be apparent to those of ordinary skill in the art from the disclosure herein. For example, an invasive blood pressure monitor can be used to calibrate a non-invasive blood pressure monitor. In addition, various types of physiological monitors can be used to calibrate various other types of physiological monitors. For example, a minimally invasive physiological monitor can be used to calibrate a non-invasive physiological monitor. Additionally, other combinations, omissions, substitutions and modifications will be apparent to the skilled artisan in view of the disclosure herein. It is contemplated that various aspects and features of the invention described can be practiced separately, combined together, or substituted for one another, and that a variety of combination and subcombinations of the features and aspects can be made and still fall within the scope of the invention. Furthermore, the systems described above need not include all of the modules and functions described in the preferred embodiments. Accordingly, the present invention is not intended to be limited by the recitation of the preferred embodiments, but is to be defined by reference to the appended claims.