Diabetes management

Details Diabetes management Diabetes management

1998-05-21

2002-07-16

Teska, Kevin J. (Department: 2123)

Data processing: structural design, modeling, simulation, and em

Simulating nonelectrical device or system

Biological or biochemical

C703S002000

Reexamination Certificate

active

06421633

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to the management of diabetes and more particularly to a method and apparatus for monitoring the effectiveness of diabetes treatment.
BACKGROUND OF THE INVENTION
In the treatment of diabetes, a patient is required to regularly check his blood glucose level using a self-testing kit. By comparing the result of a self-test with the blood glucose level which he would consider normal, the patient is able to estimate the amount of insulin which should be taken in order to bring his blood glucose level back towards that normal. Self-testing kits used for this purpose have today become very sophisticated and reliable and provide an excellent means for the short term control of diabetes. However, diabetic patients can also suffer problems arising from their condition which only become apparent in the longer term. An individual blood glucose measurement obtained by a self-test provides little or no indication of the onset of such long term problems.
The basic problem which diabetic patients have relates to the transfer of sugar, contained in the blood, across cell membranes. This problem in turn makes it difficult for the body to maintain sugar levels in the blood at the correct level. Too much blood sugar (e.g. due to the patient injecting too little insulin) and the patient becomes hyperglycaemic while too little blood sugar (e.g. due to the patient injecting too much insulin) may cause the patient to become hypoglycaemic. In particular, excessive levels of sugar in the blood result in sugar combining with protein to form glycosylated protein. Glycosylated protein is substantially insoluble and gives rise to thickening of the walls of veins and arteries, and thickening of the myelination of nerves.
One particular form of glycosylated protein is glycosylated haemoglobin. As glycosylated haemoglobin tends to remain in the blood in the long term, it provides an excellent indication of the level of glycosylated protein in the blood and therefore of the effectiveness of the treatment regime which a patient has been following, as well of course as indicating how well the patient is following that regime.
Glycosylated haemoglobin is composed of three components; namely, HbA
1A
, HbA
1B
, and HbA
1C
. The HbA
1C
level in particular is commonly measured by laboratory test in order to provide information on the long term effectiveness of diabetes treatment. The HbA
1C
level reflects the effectiveness of blood glucose treatment over the 6-8 week period preceding the HbA
1C
measurement. It has been shown that a low level of HbA
1C
in a diabetic patient's blood is a good indication that the treatment regime is effective and the risk of secondary problems related to glycosylated haemoglobin is low. The level of namely HbA
1C
in a healthy person's blood is between 4 and 6% of the total haemoglobin while in a diabetic person the level may be significantly higher (e.g. greater than 8%). It is generally sought to reduce the level of HbA
1C
in a diabetic patient's blood to between 6 and 7%.
Due to the often scarce nature of health service resources, and for the sake of convenience and practicality, the HbA
1C
level in a patient's blood is generally tested only every 3 to 4 months. However, given that the HbA
1C
level provides an indication of the effectiveness of treatment over the previous 6 to 8 weeks, long periods of ineffective treatment, and therefore damage to a patient's health, can go undetected with current testing regimes.
The article ‘A Theoretical Model to Predict the Behaviour of Glycosylated Hemoglobin Levels’ by Kirk W. Beach, J. theor. Biol. (1979) 81,547-561, describes a mathematical model for predicting the level of glycosylated haemoglobin from the blood glucose level. This model is however extremely crude and makes use of the simplification that the blood glucose level is either constant, changing only by way of a small number of discrete steps, or varying sinusoidally. Application of the model to a real patient necessarily involves a great over-simplification of the behavior of blood glucose levels.
It is an object of the present invention to overcome or at least mitigate disadvantages of known diabetes management techniques.
It is a further object of the present invention to provide a method and apparatus for providing a substantially continuous estimate of glycosylated haemoglobin component levels.
SUMMARY OF THE INVENTION
According to a first aspect of the present invention there is provided a method of predicting the level of a glycosylated haemoglobin component in a patient's blood using previously measured blood glucose and glycosylated haemoglobin component levels, the method comprising:
deriving a mathematical model of the behavior of the glycosylated haemoglobin component level relative to the blood glucose level using previously measured levels;
updating the model when a new glycosylated haemoglobin component level is measured using that new measurement and recent new blood glucose level measurements; and
applying the mathematical model to predict the glycosylated haemoglobin component level, between measurements of that level, using measurements of blood glucose level obtained since the last glycosylated haemoglobin component measurement.
Typically, blood glucose level measurements are made at a considerably higher frequency than glycosylated haemoglobin component measurements. The method of the present invention may therefore be used to predict the current glycosylated haemoglobin component level in a patient's blood using blood glucose level measurements obtained since the last glycosylated haemoglobin component level measurement. As the model is updated each time a new HbA
1C
measurement is made, the model is capable of tracking changes in the physiology of the patient which cause the behavior of the HbA
1C
level to change with respect to the blood glucose level. Changes in the blood glucose measurement pattern, i.e. the times at which the patient makes blood glucose measurements, can also be accounted for.
Preferably, the mathematical model is a parametric model or a semi-parametric model, where the model is defined by one or more model coefficients and a model equation which relate blood glucose level to the glycosylated haemoglobin component level. More preferably, the model equation relates the glycosylated haemoglobin component level to one or more parameters which describe, at least in part, the behavior (e.g. distribution) of the blood glucose level over a preceding, relatively short, time interval.
The model equation may be a linear equation in which case said model coefficients are the linear coefficients of the equation. The linear equation is of the form:
y=p
1
h
1
+p
2
h
2
+. . . p
q
h
q
+c
where y is the predicted glycosylated haemoglobin level, p are the linear model coefficients, h are the parameters which describe blood glucose level behavior, and c is a constant.
Preferably, the behavior of the blood glucose level over said short time intervals may be described using one or more gaussian functions which model the distribution of blood glucose level measurements. Said one or more parameters (h) may be chosen from the mean, variance, and amplitude of the gaussian function(s) or may be derived therefrom.
In the case of a parametric or semi-parametric model, the model may be updated following each glycosylated haemoglobin component level measurement by recalculating said model coefficients (p). In an alternative embodiment of the present invention, the coefficients of the parametric model are adapted following each new glycosylated haemoglobin level measurement using an adaptive algorithm. One suitable adaptive algorithm is Widrows algorithm. Such adaptive algorithms are arranged to reduce the error between the predicted glycosylated haemoglobin level and the measured glycosylated haemoglobin level.
The glycosylated haemoglobin component predicted using the method of the above first aspect of the present invention is one of HbA
1A
, HbA

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