Glucose monitoring system - Patent Review 5497772

Claims

What is claimed is:

1. A glucose monitoring system comprising:

an enzymatic glucose sensor adapted to be positioned within a blood stream of a person whose blood glucose concentration is to be measured, said glucose sensor including means for generating a sensor signal that is inversely proportional to the concentration of sensed glucose in the blood stream, said glucose sensor comprising an oxygen detector that detects the amount of oxygen in a region of a prescribed enzyme held within said glucose sensor, and wherein glucose and oxygen in the blood stream react with said prescribed enzyme such that the amount of oxygen is inversely proportional to the glucose concentration, and wherein said oxygen detector comprises

a first working electrode (W1), a collector electrode (C), a reference electrode (R), and a second working electrode (W2), all of said first and second working electrodes, reference electrode and collector electrode being enclosed within a first membrane wherein an ionic solution is maintained, and said first membrane being enclosed within a second membrane,

said prescribed enzyme being confined to a window region near said first working electrode,

electrical means for causing an electrical current to flow between said collector electrode and said first and second working electrodes, and

means for measuring how much current flows from said first and second working electrodes when a prescribed trim voltage is maintained across said reference electrode and said first and second working electrodes, the ratio of said currents comprising said sensor signal, which sensor signal provides a measure of oxygen in the blood stream in the vicinity of said glucose sensor; and

a glucose monitor electrically coupled to the glucose sensor, said monitor comprising

means for receiving the sensor signal,

means for processing the sensor signal and generating a glucose concentration data signal therefrom,

means for storing the glucose concentration data signal,

means for monitoring the glucose concentration data signal over a prescribed period of time and generating a rate of change signal that indicates how rapidly the glucose concentration data signal is changing,

means for selectively displaying the glucose concentration data signal and the rate of change signal,

first alarm means for determining if the glucose concentration data signal exceeds a preset level limit, and if so, generating a first alarm signal,

second alarm means for determining if the rate of change signal exceeds a preset trend limit, and if so, generating a second alarm signal,

calibration means for periodically calibrating the sensor so that it provides an accurate measure of the glucose concentration in the blood stream, and

control means for controlling the monitor so that it performs at least one of a plurality of monitoring functions as selected by a user of said monitor.

2. The glucose monitoring system as set forth in claim 1 wherein said prescribed enzyme comprises glucose oxidase.

3. The glucose monitoring system as set forth in claim 1 wherein said calibration means includes means for normalizing a ratio of said currents with a calibration constant, said calibration constant being obtained from an independent measure of the glucose concentration in a blood sample taken from the blood stream.

4. The glucose monitoring system as set forth in claim 3 wherein said glucose monitor further includes means for issuing a calibration message in the event said independent measure of the glucose in the blood sample has not been taken within a prescribed period from a prior calibration.

5. The glucose monitoring system as set forth in claim 3 wherein said calibration means further includes means for downloading calibration data to said glucose monitor at the time that a particular glucose sensor is first coupled to said glucose monitor, said calibration data being generated at the time of manufacture of said glucose sensor.

6. The glucose monitoring system as set forth in claim 5 wherein said calibration data is stored in a memory chip that is secured to a package in which a particular glucose sensor is shipped, and wherein said glucose monitor includes means for downloading the calibration data from said memory chip.

7. The glucose monitoring system as set forth in claim 1 wherein said glucose monitor includes a flat display of at least four inches by four inches overlaid with a touch sensitive screen, and wherein said control means comprises means for displaying one of a plurality of menus on said display, each of said plurality of menus including at least one button labeled with a monitoring function, and wherein said touch sensitive screen includes means for sensing if said display is touched by a user of said glucose monitor at a button of said menu, and if so, carrying out the function specified by said button.

8. The glucose monitoring system as set forth in claim 7 wherein said means for displaying further comprises at least one button for displaying the glucose concentration data signal in large numbers that substantially fill said flat display.

9. The glucose monitoring system as set forth in claim 1 wherein said glucose sensor is electrically coupled to said glucose monitor through a coupling cable that provides direct electrical contact between the glucose monitor and the glucose sensor.

10. The glucose monitoring system as set forth in claim 9 wherein said glucose sensor includes two glucose sensors, each requiring electrical contact with five separate electrical contacts, and wherein said coupling cable comprises a nine conductor cable, one of the five electrical contacts of each sensor comprising a common contact that is shared between the two glucose sensors on a single conductor of said nine conductor cable.

11. The glucose monitoring system as set forth in claim 1 wherein said glucose sensor is coupled to said glucose monitor through a contactless coupling that electrically isolates said glucose sensor from said glucose monitor.

12. The glucose monitoring system as set forth in claim 11 wherein said contactless coupling comprises a transformer coupling.

13. The glucose monitoring system as set forth in claim 11 wherein said contactless coupling comprises an optical coupling.

14. The glucose monitoring system as set forth in claim 11 wherein said contactless coupling includes signal processing means on a sensor side of said coupling, said signal processing means including means for encoding the sensor signals passed through to the glucose monitor with sensor source information.

15. The glucose monitoring system as set forth in claim 14 wherein said contactless coupling further includes a memory element having calibration data stored therein unique to said glucose sensor, and a battery on the sensor side of said coupling, said battery providing a source of continuous power to said glucose sensor.

16. The glucose monitoring system as set forth in claim 15 wherein said battery is installed within said contactless coupling at the time of manufacture of said glucose sensor, whereby said glucose sensor is continuously active from its time of manufacture, whereby said glucose sensor need not go through a calibration sequence or stabilizing sequence when first connected to said glucose monitor.

17. The glucose monitoring system as set forth in claim 15 wherein said contactless coupling includes at least one magnet and a metal member to which said magnet is attracted, the magnet or metal member being located on the sensor side of the coupling, and the other of the magnet or metal member being located on a monitor side of the coupling, said magnet having a magnetic force field that pulls the magnet toward the metal member, said magnetic force field thereby holding said contactless coupling together.

18. The glucose monitoring system as set forth in claim 1 wherein said glucose sensor is coupled to said glucose monitor through a contactless coupling that electrically isolates said glucose sensor from said glucose monitor.

19. The glucose monitoring system as set forth in claim 18 wherein said contactless coupling comprises a transformer coupling.

20. The glucose monitoring system as set forth in claim 18 wherein said contactless coupling comprises an optical coupling.

21. The glucose monitoring system as set forth in claim 18 wherein said contactless coupling further includes a memory element having calibration data stored therein unique to said glucose sensor, and a battery on the sensor side of said coupling, said battery providing a source of continuous power to said glucose sensor.

22. The glucose monitoring system as set forth in claim 21 wherein said battery is installed within said contactless coupling at the time of manufacture of said glucose sensor, whereby said glucose sensor is continuously active from its time of manufacture, whereby said glucose sensor need not go through a calibration sequence or stabilizing sequence when first connected to said glucose monitor.

23. The glucose monitoring system as set forth in claim 21 wherein said contactless coupling includes at least one magnet and a metal member to which said magnet is attracted, the magnet or metal member being located on the sensor side of the coupling, and the other of the magnet or metal member being located on a monitor side of the coupling, said magnet having a magnetic force field that pulls the magnet toward the metal member, said magnetic force field thereby holding said contactless coupling together.

24. A method of measuring a glucose concentration in the blood of a patient comprising:

(a) inserting a plurality of glucose sensor assemblies into a vein of a patient, each of said glucose sensors having a reference electrode, a collector electrode and first and second working electrodes;

(b) applying a voltage to said electrodes so as to cause first and second electrical currents to flow through said first and second working electrodes, respectively, and measuring said first and second electrical currents, the ratio of said second electrical current to said first electrical current providing a measure of oxygen in the patient's blood;

(c) placing a glucose oxidase enzyme at said first working electrode, said glucose oxidase enzyme reacting with the oxygen and glucose in the blood such that the amount of oxygen measured at said first electrode is inversely proportional to the glucose concentration in the blood;

(d) determining the glucose concentration in the blood based on said measure of oxygen and calibration constants associated with each of said glucose sensors;

(e) comparing the glucose concentration measured by each of said plurality of sensors to determine if the respective plurality of glucose concentration measurements are within a prescribed of each other, and if so, combining the plurality of glucose concentration measurements to form a composite glucose measurement, and if not, rejecting the plurality of glucose measurements as being inaccurate;

(f) storing the composite glucose measurement as a function of time;

(g) computing a rate-of-change signal for the composite glucose measurement that indicates how said composite glucose measurement has varied over a specified period of time;

(h) comparing the composite glucose measurement formed most recently and the rate-of-change signal to preprogrammed limits, and generating an alarm signal in the event the preprogrammed limits are exceeded; and

(i) selectively displaying the composite glucose measurement and rate-of-change signal.

25. A glucose monitoring system comprising:

a glucose assembly comprising a plurality of glucose sensors, each glucose sensor comprising an enzymatic glucose sensor adapted to be positioned within a blood stream of a person whose blood glucose concentration is to be measured, each glucose sensor of the glucose assembly providing a respective sensor signal that varies as a function of sensed glucose in the blood stream; and

a glucose monitor electrically coupled to the glucose assembly, said glucose monitor comprising

means for receiving the sensor signal from each glucose sensor,

means for processing the sensor signal received from each glucose sensor, said means for processing including means for comparing the sensor signals obtained from each of said plurality of sensors and generating a composite sensor signal only if the respective sensor signals are within a first prescribed amount of each other,

means for storing the composite sensor signal,

means for monitoring the composite sensor signal over a prescribed period of time and generating a rate of change signal that indicates how rapidly the composite sensor signal is changing,

means for selectively displaying the composite sensor signal and the rate of change signal,

first alarm means for determining if the composite sensor signal exceeds a preset level limit, and if so, generating a first alarm signal,

second alarm means for determining if the rate of change signal exceeds a preset trend limit, and if so, generating a second alarm signal,

calibration means for periodically verifying that each glucose sensor of the sensor assembly provides an accurate measure of the glucose concentration in the blood stream, and

control means for controlling the monitor so that it performs at least one of a plurality of monitoring functions as selected by a user of said monitor.

26. The glucose monitoring system as set forth in claim 25 wherein said processing means further includes means for generating an error message in the event that the respective sensor signals are not within said first prescribed amount of each other, said error message advising a user of said glucose monitor to check said plurality of glucose sensors.

27. The glucose monitoring system as set forth in claim 26 wherein said processing means further includes shutdown means for automatically shutting down said glucose monitor in the event at least one of the sensor signals differs from the others of said sensor signals by more than a second prescribed amount.

28. The glucose monitoring system as set forth in claim 25 further including at least one additional sensor adapted to sense a parameter other than glucose concentration, and wherein said processing means includes means for combining all of the sensor signals in arriving at said composite sensor signal.

BACKGROUND OF THE INVENTION

The present invention relates to glucose monitoring systems and methods, and more particularly to a system that monitors the amount and rate of change of glucose in a patient, providing an easy-to-read display of such monitored information, as well as an alarm if either the amount or rate of change exceeds programmable limits.

Glucose is a simple sugar containing six carbon atoms (a hexose). Glucose is an important source of energy in the body and the sole source of energy for the brain. Glucose is stored in the body in the form of glycogen. In a healthy person, the concentration of glucose in the blood is maintained at around 5 mmol/l by a variety of hormones, principally insulin and glucagon. If the blood-glucose concentration falls below this level neurological and other symptoms may result, such as hypoglycemia. Conversely, if the blood-glucose level is raised above its normal level, e.g., to above about 10 mmol/l, the condition of hyperglycemia develops, which is one of the symptoms of diabetes mellitus. It is thus evident that maintaining the concentration of glucose in the blood at a proper level is critically important for wellness and good health.

Unfortunately, some individuals, either through disease, dramatic and/or sudden changes to the body (such as may be caused by injury or surgery), or for other reasons, are unable to maintain the proper level of glucose in their blood. In such instances, the amount of glucose can usually be altered, as required, in order to bring the glucose concentration to a proper level. A shot of insulin, for example, can be administered in order to decrease the glucose concentration (insulin decreases the amount of glucose in the blood). Conversely, glucose may be added directly to the blood through injection, an intravenous (IV) solution, or indirectly by eating or drinking certain foods or liquids.

Before the glucose concentration can be properly adjusted, however, an attending physician (or the patient himself or herself), must know what the present glucose concentration is and whether such concentration is increasing or decreasing. Unfortunately, the only viable technique heretofore available for measuring glucose concentration has been by drawing a blood sample and directly measuring the amount of glucose therein, or by measuring the amount of sugar in the urine. Both measurement techniques are not only inconvenient for the patient, but also may require significant time, manpower, and the use of expensive laboratory instruments, tools or aids to complete. As a result, it is usually not possible for a physician to know immediately what the glucose concentration of a given patient is. Rather, fluid samples must first be obtained, tested or analyzed, and a report issued. Based on such report, appropriate corrective action can then be taken when needed, e.g., through insulin injections or IV supplements, to move the glucose concentration back to an acceptable level. Unfortunately, however, because of the inherent time delay involved with gathering the fluid samples, performing the analysis, and issuing the report, such corrective action may not be possible until several hours after it is first needed. Even after the report is issued, the report results may be misinterpreted, or (e.g., through transcription or analysis error) may simply be wrong. Hence, it is apparent that what is needed is a way to accurately determine the glucose concentration of a patient immediately, effectively communicate such measured concentration to a physician or other interested person (including the patient) with minimum likelihood of error, and provide a clear indication of whether such concentration is within certain prescribed safe limits.

Even after the glucose concentration is known, the physician must still estimate how much corrective action is required until such time as a direction and rate of change of the glucose concentration level has been established. Unfortunately, to identify a trend in the glucose concentration using existing techniques, i.e., to determine whether the glucose concentration is increasing or decreasing, and at what rate, a series of the above-described body fluid measurements must first be made, and the results then analyzed. Such measuring and analyzing process only further delays any appropriate corrective action. What is clearly needed, therefore, is a glucose measurement system that provides a physician, or other medical personnel (or the patient himself or herself) with a rapid measure or indication of the rate of change of the glucose concentration, thereby immediately informing the physician whether any corrective action is needed.

The present invention advantageously addresses the above and other needs.

SUMMARY OF THE INVENTION

The present invention provides a glucose monitoring system that continuously measures the glucose concentration in a patient's blood, and provides an indication of the rate of change of such concentration. The system further automatically determines whether the measured concentration and rate of change are within certain preset limits, and if not, generates an alarm signal.

The glucose monitoring system includes a glucose sensor that is inserted into the venous system of the patient, where it responds to blood glucose and produces electrical signals that are related to the glucose concentration. The electrical signals generated by the glucose sensor ("sensor signals") are delivered through a suitable interconnect cable to a glucose monitor. The glucose monitor interprets the sensor signals by applying a previously determined calibration to quantitatively determine the blood glucose value. The blood glucose value thus determined is then processed in order to determine the rate of change, is stored (to create a history or record), and may also be displayed. One selectable display mode displays the measured concentration in large, easy-to-read numerals, with selectable units, e.g., milligrams (mg) per deciliter (dl), or mg/dl. Another selectable display mode displays a graph of the rate of change (trend) in accordance with selected units, such as mg/dl/hr. Such graph provides an easy-to-see representation of the glucose concentration over a past period of time, e.g., three hours.

The glucose monitor stores the blood glucose value and other data (including the patient name, sensor identification number, start date, etc.) in memory and displays the measured glucose level, updating the displayed level periodically (e.g., once per minute). Such stored data may also advantageously be viewed, as selected, as a graphic display that indicates the last several hours of recorded values, thereby clearly showing any trends in the data over such time period.

In accordance with one aspect of the invention, a plurality of glucose sensors, e.g., at least two glucose sensors, are inserted into a vein of the patient and are coupled to the glucose monitor, with a glucose concentration measurement being provided by each sensor. A prescribed degree of correlation must exist between the readings from each sensor in order to validate the correctness of the concentration measurement that is made. If the prescribed degree of correlation does not exist, then the monitor automatically indicates that a recalibration and/or new sensor is required.

In accordance with a further aspect of the invention, some of the plurality of sensors coupled to the monitor may be other than glucose sensors, e.g., a sensor to detect oxygen, hydrogen peroxide, or other substances or elements of interest that are present in the patient's blood. The monitor, in such instances, may process and combine the measurements from each sensor, e.g., combining the measurement from one sensor with the measurement from another sensor, as required, in order to provide an overall evaluation of the condition, well-being and/or health of the patient.

In accordance with another aspect of the invention, the glucose monitor includes a data card port that allows the current glucose data to be stored in a data card that can be selectively removed from the monitor in order to indirectly make such glucose data available to another computer or processor, or to make such data available for analysis at a later time. The glucose monitor may further include, in one embodiment, an RS-232 (serial) port that allows the monitor to be connected directly to a computer network, or other computer equipment, to facilitate the direct transfer of the glucose data to such other computer network or equipment.

In accordance with an additional aspect of the invention, the glucose monitor is controlled via on-screen menus that define the various subroutines or processes carried out by the monitor at any given time. The screen menus are readily accessed, in a preferred embodiment, by simply touching a designated area of a touch sensitive screen. A user of the glucose monitor may readily "jump" between the main menu and any of the subroutines or processes by merely pressing or touching an appropriate MENU button or key displayed on the touch sensitive screen.

In accordance with yet a further aspect of the invention, the glucose monitoring system is calibrated with each new glucose sensor. Further, periodically, e.g., once every 24 hours, the system is calibrated against a blood sample that has been independently analyzed by a certified reference method for glucose concentration.

It is therefore a feature of the invention to provide a glucose monitoring system that continuously monitors the glucose concentration of a patient, providing real-time readings and a history of a patient's blood glucose concentration, including the rate at which the glucose concentration is changing. Such system is particularly suited for use in a hospital environment or other in-patient setting. Such system is also adaptable to any language or units of measure.

It is another feature of the invention to provide such a glucose monitoring system that displays the measured glucose concentration in large, easy-to-read numerals that can be seen from across the room, or even from outside of the room (e.g., just by looking into the room where the patient is situated).

It is an additional feature of the invention to provide such a glucose