WO2006097933A2

WO2006097933A2 - Method for monitoring changes in blood glucose level

Info

Publication number: WO2006097933A2
Application number: PCT/IL2006/000344
Authority: WO
Inventors: Gabriel Bitton; Benny Pesach; Leonid Grinberg; Amit Antebi; Ron Nagar; Adam Heller
Original assignee: Glucon Inc.
Priority date: 2005-03-17
Filing date: 2006-03-16
Publication date: 2006-09-21
Also published as: WO2006097933A3

Abstract

A method of monitoring changes in blood glucose level of a patient comprising: illuminating at least one region of the skin with light that stimulates photoacoustic waves in a marker substance in the blood; and using the photoacoustic waves to measure changes in blood glucose.

Description

METHOD AND APPARATUS FOR MONITORING GLUCOSE RELATED APPLICATIONS

The present application claims benefit under 35 U.S. C. 119(e) of U.S. Provisional application 60/662,349 filed March 17, 2005, the disclosure of which is incorporated herein by reference.

FIELD OF THE INVENTION

The invention relates to non-invasive in-vivo methods and apparatus for monitoring blood glucose concentration.

BACKGROUND OF THE INVENTION Methods and apparatus for determining blood glucose levels for use in the home, for example by a diabetic who must monitor blood glucose levels frequently, are available. These methods and associated devices are generally invasive and usually involve taking blood samples by finger pricking. Often a diabetic must determine blood glucose levels many times daily and finger pricking is perceived as inconvenient and unpleasant. To avoid finger pricking, diabetics tend to monitor their glucose levels less frequently than is advisable.

Non-invasive in-vivo methods and apparatus for monitoring blood glucose are known.

PCT Publication WO 98/38904, the disclosure of which is incorporated herein by reference, describes a "non-invasive, in-vivo glucometer" that uses a photoacoustic effect to measure a person's blood glucose. PCT Publication WO 02/15776, the disclosure of which is incorporated herein by reference, describes locating a blood vessel in the body and determining glucose concentration in a bolus of blood in the blood vessel. The glucose concentration in the blood bolus is determined by illuminating the bolus with light that is absorbed and/or scattered by glucose to generate photoacoustic waves in the bolus. Intensity of the photoacoustic waves, which is a function of glucose concentration, is sensed and used to assay glucose in the bolus.

Wearable devices for assaying glucose are known, are generally based on near- infrared (NIR) spectroscopic methods and usually comprise a light source and optical detector that are attached to the patient's finger, wrist or other part of the body. Wearable NIR devices for assaying glucose are described in US Patent 6,241,663 to Wu, et al. and US Patent 5,551,422, to Simonsen et al., the disclosures of which are incorporated herein by reference.

US patent application publication US 2005/0010090 Al, the disclosure of which is incorporated herein by reference, describes a method of monitoring glucose responsive to changes in water content in various fluid compartments of the body. The total liquid content of the body, conventionally referred to as total body water (TBW), is considered to be comprised in two major "fluid compartments", an intracellular fluid (ICF) compartment and an extracellular fluid (ECF). The ICF comprises the aggregate of fluids maintained within the body cells. The ECF comprises an interstitial fluid (ISF) "sub- compartment" that surrounds and bathes the body cells and an intravascular fluid (IVF) compartment, i.e. blood, carried by the vascular system. For convenience, the various compartments and sub-compartments are referred to as compartments.

The healthy body tends to maintain relatively stable, normative ratios between the volumes of its various fluid compartments and equilibrium between their osmolarities. As a result, changes in concentration of an osmolyte in a fluid compartment of the body tends to generate a shift in the water content of the compartments in order to equilibrate osmolarities between the compartments. For example, a change in the concentration of blood glucose in general generates a change in the water content of the blood that tends to equilibrate the osmolarities between the blood and the extracellular and intracellular fluids. If blood glucose concentration increases or decreases, water in general shifts respectively into or out from the blood to equilibrate osmolarities between the blood, and the interstitial and intracellular fluids. The water shift into or out from the blood results in an increase or decrease respectively of blood volume and shrinking or swelling respectively of the ISF compartment and/or ICF compartment. The US patent application publication 2005/0010090A 1, referenced above notes that

"Because water has a large NIR signal that is relatively easy to measure compared to glucose a calibration based at least on part on the compartmental activity of water has a magnified signal related to glucose." The application describes an NIR spectrometer used to measure glucose concentration that transmits NIR light into a region of the skin at wavelengths that interact strongly with water and collects and generates signals responsive to light from the NIR that is diffusively reflected or transflected by tissue in and beneath the skin region. The signals are processed using a calibration model to determine glucose concentration.

Hereinafter, apparatus for measuring glucose concentration is, generally, referred to as a "glucometer". SUMMARY OF THE INVENTION

An aspect of some embodiments of the present invention relates to providing methods and apparatus for non-invasively monitoring a patient's blood glucose concentration. An aspect of some embodiments of the invention relates to using a photoacoustic effect that is responsive to changes in the volume of at least one fluid compartment in a patient's body and using the measured changes to provide a measure of the patient's blood glucose and/or changes therein. In accordance with an aspect of an embodiment of the invention, the at least one fluid compartment comprises the patient's blood. A photoacoustic effect is used to assay a marker substance, or determine a function of a marker substance, in the patient's blood that changes in response to changes in blood volume.

A fluid compartment marker substance, also referred to as a "marker", is a substance whose total quantity in the fluid compartment is substantially constant during a period of time for which it is used to measure changes in the fluid compartment's volume. Changes in the marker assay and/or function of the marker concentration as measured by the photoacoustic effect are correlated with changes in the volume of the patient's blood. Changes in blood volume and/or photoacoustic signals responsive to the changes in blood volume are correlated with changes in glucose concentrations in the blood and are used to provide measures of changes in glucose concentration. Optionally, a marker substance for the blood is hemoglobin (Hb), red blood cell count (RBC), and/or hematocrit (Hct) {i.e. packed red cell volume (PCV)). For convenience, hereinafter, concentration of a marker and a function thereof are referred to generically as "concentration" of the marker. In an embodiment of the invention, a reference assay of blood glucose is determined for normalizing assays provided by photoacoustic measurements and/or to which changes in glucose concentrations as determined from photoacoustic measurements are added to provide glucose assays. Optionally, the reference assay is determined using any of various conventional methods and devices known in the art from a sample of blood drawn from the patient.

In accordance with an aspect of an embodiment of the invention, the at least one fluid compartment comprises the patient's interstitial fluid (ISF) compartment. Changes in the ISF volume are correlated with changes in glucose concentrations in the blood and photoacoustic measurements responsive to the volume changes are used to monitor changes in the glucose concentration. An assay of blood glucose is optionally provided responsive to the monitored changes and a reference assay.

In accordance with an embodiment of the invention, to monitor ISF volume changes, a photoacoustic effect is used to provide a measure of changes in the thickness of the patient's skin and/or a layer or layers therein. The skin, and in particular the corium or dermis of the skin, is a major repository of body water, containing as much as 17% of the body's interstitial fluid (ISF), and thickness of the skin and/or the dermis are correlated with changes in ISF volume. The photoacoustic measurements of changes in the patient's skin thickness and/or layers therein are used to monitor changes in the volume of the patient's ISF. The changes in skin thickness, ISF volume and/or the photoacoustic signals responsive to changes in skin thickness are used to monitor changes in glucose concentration. Photoacoustic methods of determining skin thickness are described in US patent application entitled, "A Method for Monitoring Body Fluids", Attorney Docket No 2227/04847, filed January 31, 2006, the disclosure of which is incorporated herein by reference and any of the described methods may be used to monitor skin thickness and therefrom changes in ISF volume.

Whereas the inventors have found that monitoring concentration of a marker substance in the blood using a photoacoustic effect or monitoring changes in ISF volume by monitoring skin thickness can provide measurements that are highly correlated with blood glucose, fluid shifts between fluid compartments in the body and changes in the body's fluid compartment volumes are, in general, complicated. Fluid shifts can change directions in relatively short periods of time, depend inter alia on motion of more than a single osmolyte between fluid compartments and can be influenced strongly by changes in posture. Mathematical models of water shift between compartments due to osmolarity change in one of the compartments are described in an article by C. C. GYENGE, et al; "Transport of Fluid and Solutes in the Body I. Formulation of a Mathematical Model"; Am J Physiol Heart Circ Physiol 277: H1215- Hl 227, 1999 and in an article in the same journal by the same authors entitled "Transport of Fluid and Solutes in the Body II. Model Validation and Implications"; Am J Physiol Heart Circ Physiol 277: H1228-H1240, 1999. The disclosures of the above cited articles are incorporated herein by reference.

The inventors have determined that in view of the relatively complicated processes involved in fluid compartment volume changes, monitoring changes in more than one fluid compartment of a patient's body can improve reliability and accuracy of measures of the patient's glucose. According to an aspect of some embodiments of the invention, photoacoustic effects are advantageously employed to substantially simultaneously, and non- invasively, monitor changes in the volumes of a plurality of fluid compartments. The changes in the fluid volumes are used to monitor changes in a patient's blood glucose. In an embodiment of the invention, the plurality of fluid volumes comprises the patient's ISF and blood volumes.

Measuring volume changes in more than one fluid compartment can often provide indications of causes of changes in blood glucose concentration. For example, a temporary decrease in concentration of a marker in the blood may result simply from a patient drinking a large amount of water rather than an increase in blood glucose. Whereas a marker assay decrease resulting from an increase in glucose concentration will in general be accompanied by a decrease in ISF volume, imbibition will in general result in a substantially simultaneous increase in both blood volume and ISF volume. The two situations, which both result in an increase in blood volume and corresponding decrease in marker concentration, can therefore be distinguished, in accordance with an embodiment of the invention by monitoring ISF volume in addition to monitoring blood volume.

An aspect of some embodiments of the invention relates to acquiring measurements of the volume of at least one fluid compartment in a patient's body at a plurality of different locations in the body.

In an embodiment of the invention, correlation of changes in the fluid compartment volumes measured at different sites is used to indicate whether the changes, and concomitant changes in concentration of a marker, such as hemoglobin, are caused by postural changes. Optionally, a patient's fluid compartment volumes are monitored at a site in an upper region of the body and at a site in a lower region of the body. If the patient changes from a prone to an upright position or from sitting to standing, water shifts from the upper part of the body to the lower part of the body, resulting in a local increase in all fluid volumes in the lower part of the body. It is noted however, that swelling of the ISF compartment is a result, at least in part, of shift of water from the blood to the ISF. As a result of blood pooling in the lower part of the body, fluid filtrates out from the blood through the capillaries in the lower part of the body and into the ISF compartment. The overall blood volume therefore decreases. Since blood maintains substantially a same composition throughout the body, marker concentration will in general show an increase substantially independent of where in the body it is measured. On the other hand, a local measure, such as skin thickness, of ISF volume, in the lower part of the body will show an increase in ISF volume in comparison to a local measure of ISF volume in the upper part of the body. Similarly, if the patient "returns" from the upright position to the prone position or from standing to sitting, water shifts from the lower to the upper part of the body and from the ISF back to the blood. The change in posture results in a decease in concentration of the blood marker, decrease in ISF volume measured in the lower part of the body and increase in ISF volume measured in the upper part of the body. For situations in which fluid volume changes are due to postural changes, changes in volume of the ISF fluid compartment measured at the upper site are therefore, generally, negatively correlated with changes in the ISF volume at the lower site and with Hb blood concentration. On the other hand, volume changes in ISF at the lower site and Hb concentration in the blood that are caused by postural changes are positively correlated.

In an embodiment of the invention, a "fluid volume" glucometer comprises at least one light source that provides light to stimulate photoacoustic waves in the skin and in blood and at least one acoustic transducer that senses the photoacoustic waves and generates signals responsive thereto. Optionally, the at least one light source provides light at a wavelength that is relatively strongly absorbed by ISF and/or components of the ISF and/or at a wavelength that is relatively strongly absorbed by a marker in the blood. In an embodiment of the invention, the wavelength of light that is relatively strongly absorbed by ISF is a wavelength, such as 1440 nm, at which light is relatively strongly absorbed by water. Optionally, the marker in blood is hemoglobin and the wavelength of light that is relatively strongly absorbed by the marker, hemoglobin, is 800 nm.

To monitor changes in the blood glucose level, the glucometer is placed on the skin and the at least one light source is controlled to transmit light that illuminates the skin and blood in a blood vessel in and/or below the skin. Photoacoustic waves that the light generates are processed to determine which of the signals are generated in the skin and/or at boundaries of layers in the skin and which of the signals originate in the blood vessel. The signals that originate in the skin and/or skin boundaries provide a measure of skin thickness, which in turn is used to monitor the volume of the ISF. The signals that originate in blood in the blood vessel are used to assay a marker in the blood and the assay used to monitor blood volume. Changes in the ISF volume and in the volume of blood are used to assay the patient's blood glucose.

There is therefore provided in accordance with an embodiment of the invention a method of monitoring changes in blood glucose level of a patient comprising: illuminating at least one region of the skin with light that stimulates photoacoustic waves in a marker substance in the blood; and using the photoacoustic waves to measure changes in blood glucose. Optionally, the method comprises illuminating the at least one region of the skin with light that stimulates photoacoustic waves in the skin and using the photoacoustic waves stimulated in the at least one skin region to measure changes in blood glucose.

There is further provided in accordance with an embodiment of the invention, A method of monitoring changes in blood glucose level by monitoring changes in volumes of at least one fluid compartment of a body comprising: illuminating at least one region of the skin with light that stimulates photoacoustic waves in the skin and in a marker substance in the blood; and using the photoacoustic waves originating in the blood and in the at least one region of the skin to measure changes blood glucose. Additionally or alternatively, using photoacoustic waves stimulated in the at least one region of skin comprises using the waves to determine a change in volume of ISF fluid in the skin. Optionally, using the waves to determine a change in the ISF volume comprises using the waves to determine change in thickness of the at least one region of the skin and/or a layer thereof. In some embodiments of the invention the method comprises illuminating a blood vessel below the at least one region of the skin with light that stimulates photoacoustic waves in the blood vessel and using the waves to measure changes in blood glucose. Optionally, using the photoacoustic waves stimulated in the blood vessel below the skin comprises using the waves to determine change in thickness of the at least one region of the skin . In some embodiments of the invention the method comprises using the change in skin thickness to determine change in volume of ISF fluid in the at least one region of the skin.

In some embodiments of the invention, using photoacoustic waves stimulated in the marker comprises using the waves to determine a change in volume of the blood. Optionally, using the photoacoustic waves stimulated in the marker comprises using the waves to assay the marker in the fluid compartment.

In some embodiments of the invention the marker is at least one of hemoglobin (Hb), red blood cell count (RBC), or packed red cell volume (PCV).

In some embodiments of the invention the method comprises transmitting ultrasound into the skin and using reflections of the ultrasound from a feature in or below the skin to measure changes in glucose. Optionally, using the reflections to determine change in thickness of the skin. Optionally the method comprises using the skin thickness change to determine change in volume of ISF fluid in the skin. In some embodiments of the invention the feature is a blood vessel.

In some embodiments of the invention, the at least one region of the skin comprises a plurality of regions. Optionally the method comprises using the photoacoustic waves from different skin regions to measure changes in blood glucose.

Additionally or alternatively, using the photoacoustic waves from different regions comprises using the waves to adjust the measured change in blood glucose for changes in the patient's posture.

There is further provided in accordance with an embodiment of the invention , a method of monitoring changes in blood glucose level of a patient comprising: illuminating at least one region of the skin with light that stimulates photoacoustic waves in the body; using the photoacoustic waves to provide signals responsive to changes in a plurality of fluid volumes in the body; and using the signals to determine changes in blood glucose. Optionally, the plurality of fluid volumes comprises the blood. Optionally, the plurality of fluid volumes comprises the interstitial fluid.

In some embodiments of the invention the at least one skin region comprises a plurality of different skin regions. In some embodiments of the invention, the method comprises acquiring impedance measurements of the body and using the impedance measurements to determine changes in blood glucose. BRIEF DESCRIPTION OF FIGURES

Non-limiting examples of embodiments of the invention are described below with reference to figures attached hereto. In the figures, identical structures, elements or parts that appear in more than one figure are generally labeled with the same numeral in all the figures in which they appear. Dimensions of components and features shown in the figures are chosen for convenience and clarity of presentation and are not necessarily shown to scale. The figures are listed below.

Fig. 1 schematically shows a "photoacoustic" glucometer, being used to monitor a marker in the blood of a patient to assay the patient's blood glucose, in accordance with an embodiment of the present invention; Fig. 2A shows a graph of comparing glucose assays provided by a conventional Bayer

Glucometer and a photoacoustic glucometer for a volunteer in an experiment conducted to test performance of the photoacoustic glucometer, in accordance with an embodiment of the invention;

Fig. 2B shows a graph of comparing Hb assays provided by a conventional Hemocue hemoglobin system and the photoacoustic glucometer during the experiment for which glucose assays are shown in Fig. 2A, in accordance with an embodiment of the invention;

Fig. 3 schematically shows a photoacoustic glucometer, being used to monitor the ISF and blood volumes of a patient to assay the patient's blood glucose in accordance with an embodiment of the present invention;

Fig. 4 schematically shows signals generated by the photoacoustic glucometer shown in Fig. 3 that are used to monitor a blood marker (Hb) and skin thickness as a measure of changes in ISF volume, in accordance with an embodiment of the invention;

Fig. 5 shows results comparing glucose measurements provided by a Bayer Glucometer and skin thickness measurements provided by a photoacoustic glucometer similar to that shown in Fig. 3 in an experiment conducted to test performance of the photoacoustic glucometer, in accordance with an embodiment of the invention;

Fig. 6 schematically shows a patient wearing a glucometer that acquires photoacoustic measurements at different locations on the patient's body for providing assays of the patients glucose, in accordance with an embodiment of the invention; and

Fig. 7 schematically shows results of an experiment to determine correlation of glucose measurements with postural changes, in accordance with an embodiment of the invention.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS Fig. 1 schematically shows a glucometer 20 located on a region of the skin 30 of a patient operating to monitor the patient's blood glucose level, in accordance with an embodiment of the invention. Glucometer 20 is shown determining blood glucose responsive to concentration of a marker, optionally hemoglobin (Hb), in blood in a blood vessel 34. Skin 30 comprises the epidermis 31, the corium or dermis 32 and the subcutis 33. Subcutis 33 comprises mainly loose fibrous connective tissue and fat cells laced with blood vessels. By way of example, blood vessel 34 is a blood vessel in subcutis 33. Glucometer 20 comprises at least one light source 21 that provides pulses of light that is absorbed by Hb to stimulate photoacoustic waves in blood in blood vessel 34 and at least one acoustic transducer 22 that generates signals responsive to the photoacoustic waves. By way of example, glucometer 20 is shown comprising one light source 21 flanked by two acoustic transducers 22. Any configuration of light sources and acoustic transducers suitable for generating photoacoustic waves in blood in a blood vessel and sensing the photoacoustic waves may be used in the practice of the present invention. Photoacoustic sensors, such as those shown and described in PCT Publication WO2005/068973, the disclosure of which is incorporated herein by reference, are optionally used in the practice of the present invention.

Light in a light pulse provided by light source 21 is schematically represented by wavy arrows 41 and locations in blood vessel 34 at which photoacoustic waves are generated by the light are schematically represented by asterisks 42. For convenience, the numeral 42 is also used to reference the photoacoustic waves stimulated by light 41 at locations 42. Optionally, light source 21 provides light 41 at a wavelength, such as 800 nm, that is relatively strongly absorbed by hemoglobin to stimulate photoacoustic waves 42 in blood vessel 34. Whereas, generally, light provided by light source 21 will also generate photoacoustic waves at sites additional to those in blood vessel 34, for simplicity of presentation photoacoustic sites 42 are shown only in the blood vessel in Fig. 1. In an embodiment of the invention, glucometer 20 is configured to process photoacoustic signals and determine whether their origin is in a blood vessel and use substantially only those that are determined to originate in the blood vessel for assaying glucose. Optionally glucometer 20 determines location of a blood vessel, such as blood vessel 34, responsive to a spatial distribution of the origins of photoacoustic waves stimulated by light that is preferentially absorbed by blood. Optionally, glucometer 20 locates blood vessel 34 by controlling acoustic transducers 22 to image tissue below the surface of skin 30 using conventional ultrasound imaging techniques. Photoacoustic waves are determined to originate in the blood vessel if their origins are coincide with a region of the blood vessel.

In accordance with an embodiment of the invention, glucometer 20 periodically illuminates skin 30 with a pulse of light 41 that is absorbed by a marker, e.g. Hb, in the blood and signals generated by at least one transducer 22 responsive to photoacoustic waves 42 are processed to provide an assay of the patient's glucose. Optionally, the signals are used to determine the patient's blood volume and/or changes therein and the determined blood volume and/or changes therein are used to monitor the patient's glucose. In some embodiments of the invention, a theoretical or empirical model is used to directly correlate the photoacoustic signals with the patient's glucose. Optionally, the model is generated responsive to a calibration procedure performed on the patient and/or a group of patients. The calibration procedure optionally comprises determining correlations between photoacoustic signals and different levels of blood glucose and/or changes therein for the patient and/or group of patients. Optionally, the calibration procedure comprises determining a reference blood glucose level and corresponding photoacoustic signals to which changes in the photoacoustic signals are referenced to determine blood glucose levels and/or changes therein.

The inventors have carried out experiments to explore the correlation of photoacoustic assays of a person's Hb with the person's blood glucose concentration and the use of photoacoustic measurements of Hb as a predictor of the glucose concentration. Experiments were carried out on volunteers in accordance with various protocols known in the art that were approved by the Internal Review Board of Hadassah Hospital in Jerusalem. The protocols included infusion, OGTT, and glucose clamp protocols. The infusion protocol is discussed below and results for an infusion protocol experiment conducted with a diabetic volunteer are given in Figs. 2 A and 2B.

After fasting for 10-12 hours, the volunteers arrived in the laboratory where the experiments were conducted and were placed in a supine position. Two catheters were inserted in the cubital veins of the left and right arms of each volunteer to provide for blood withdrawal and dextrose/insulin infusion, respectively. After an initial 60 minute period of stabilization during which the volunteers rested, a 20% dextrose solution was infused at a rate of 200-250 ml/h for a period of 30 to 60 min. The dextrose infusion was then either stopped, or maintained at a rate required to provide a constant blood glucose concentration. Return to an initial blood glucose concentration was achieved either spontaneously in the non-diabetic subjects after cessation of glucose infusion and by IV injection of insulin (Humulin 100 IU/ml) in the diabetic subjects. In some instances, a cycle of dextrose infusion followed by return to a "normal" glucose level was repeated. Every 5 to 10 minutes during performance of the protocol, blood samples from each volunteer were taken and were promptly analyzed for glucose using a Bayer Glucometer Elite blood glucose analyzer and for Hb concentration, using a Hemocue hemoglobin system. The results were analyzed for correlation between the glucose concentration and Hb concentration by regression analysis. During an initial "calibration period" lasting between about 70 to 90 minutes of the protocol for each experiment, a photoacoustic glucometer similar to that shown in Fig. 1 was calibrated against measurements acquired by the Bayer Glucometer. Thereafter, the photoacoustic glucometer provided measurements of the volunteer's Hb concentration and used them to provide assays of the volunteer's blood glucose. Fig. 2A shows a graph 50 of glucose concentration measurements provided by the Bayer Glucometer and photoacoustic assays provided by the pliotoacoustic glucometer responsive to Hb concentration as a function of time for a diabetic volunteer who was intravenously infused with glucose. Glucose assays provided by the Bayer Glucometer are indicated by discrete points 52 associated with error bars. The photoacoustic assays were acquired using light at a wavelength of 1050 nanometers and are indicated by a curve 60 that connects discrete photoacoustic assays (not indicated) provided by the photoacoustic glucometer.

Time along the abscissa of graph 50 is measured in minutes and the time origin of the graph is coincident with the end of the stabilization period for the volunteer at a time when dextrose infusion to the volunteer was initiated. Dextrose was infused at a rate of between 200-250 ml/h to a time tj and thereafter was maintained at a rate that stabilized the blood glucose level at about 200 mg/dl until a time t2 at which an IV injection of insulin was administered to the volunteer. The effects of the insulin are indicted by the rapid decrease in blood glucose that begins at about time t2- At about a time ty dextrose was again infused generating a corresponding steep rise in the volunteers blood glucose.

A calibration period during which the photoacoustic glucometer was calibrated to the Bayer Glucometer lies to the left of an indicator line 62 at a time t^. Thereafter, the photoacoustic glucometer was "on its own" and assays performed by the photoacoustic glucometer are independent of assays provided by the Bayer Glucometer. From the graph it is seen that the independent photoacoustic assays track the Bayer Glucometer assays. A regression analysis of the independent photoacoustic assays and the Bayer Glucometer assays resulted in a correlation coefficient "R" shown in the upper right hand corner of graph 50 equal to about 0.88, indicating that about 0.78 of the variance in assays provided by the Bayer Glucometer is associated with variance in the assays provided by the photoacoustic glucometer.

Fig. 2B schematically show a graph 70 of Hb assays provided by the photoacoustic glucometer and the Hemocue hemoglobin system for the same volunteer and the protocol for which measurements of glucose are shown in Fig. 2A. Hb assays provided by the Hemocue system are indicated by discrete points 72 associated with error bars. The photoacoustic assays were acquired using light at a wavelength of 949 nanometers and are indicated by a curve 74 that connects discrete assay measurements (not indicated) provided by the photoacoustic glucometer. The photoacoustic glucometer is calibrated against the Hemocue system during the calibration period to the left of indicator line 62 at time t(\

From graph 70 it is seen that Hb concentration, appears to be, as expected, relatively strongly and negatively correlated with glucose concentration shown in graph 50 in Fig. 2A. As blood glucose concentration increases, extra vascular fluid shifts into the intravascular compartment diluting Hb concentrations. As blood glucose concentration decreases, fluid shifts out of the intravascular compartment increasing Hb concentration. The photoacoustic assays of Hb track those provided by the Hemocue system relatively closely and the photoacoustic and Hemocue assays have a correlation R shown in the upper right hand corner of graph 70 equal to about 0.89.

In some embodiments of the invention, glucometer 20 operates to provide photoacoustic measurements of changes in a patient's ISF volume to measure the patient's blood glucose. As in the case of blood volume measurements responsive to concentration of a marker in the blood, glucometer 20 is optionally calibrated to provide a correlation between photoacoustic measurements and/or changes in ISF volume and/or a reference ISF volume and corresponding glucose levels. In an embodiment of the invention, to monitor ISF volume changes, glucometer 20 provides a measure of the thickness of the skin and/or a layer or layers therein of the patient. The measures of changes in skin thickness are used to provide a measure of changes in the patient's glucose levels and therefrom the patient's glucose levels. Fig. 3 schematically shows glucometer 20 operating to provide photoacoustic measures of changes in ISF volume, as well as changes in blood volume that are used to determine a patient's blood glucose, in accordance with an embodiment of the invention. In Fig. 3 glucometer 20 illuminates skin 30 with pulses of light 41 that stimulate photoacoustic waves 42 in blood vessel 34 as well as in subcutis 33 and in other layers of skin 30. Optionally, glucometer 20 periodically illuminates skin 30 with pulses of light 41 at a plurality of wavelengths. Optionally, for at least one of the plurality of wavelengths, such as for example at 1440 nm, light is relatively strongly absorbed by water. Optionally, for at least one of the plurality of wavelengths, such as for example at 800 nm, light is relatively strongly absorbed by hemoglobin. Optionally for at least one of the wavelengths, such as 960 nm or 1300 nm, light is relatively strongly absorbed by both water and hemoglobin. Signals generated by at least one transducer 22 responsive to photoacoustic waves in skin 30 and blood vessel 34 are processed to determine thickness of the skin as well as to assay hemoglobin in the blood vessel. Changes in the determined skin thickness, as well as changes in hemoglobin assay as described above, are used to monitor changes in the patient's blood glucose level.

Fig. 4 schematically shows a graph 150 of a signal generated by at least one acoustic transducer 22 when glucometer 20 illuminates skin 30 with a pulse of light at a wavelength at which light is relatively strongly absorbed by hemoglobin and generates photoacoustic waves 42 in blood vessel 34 but also throughout skin 30, in accordance with an embodiment of the invention. A curve 152 shows the amplitude of the signal in arbitrary units indicated along the ordinate of graph 150 as a function of time indicated in nanoseconds along the abscissa of the graph. A first negative peak 161 (polarity of peak 161 and other peaks is arbitrary and a function of the configuration of at least one transducer 22) in signal 152 is generated by at least one transducer 22 in response to light reflected from the surface of skin 30 that is incident on the at least one transducer. The light causes local heating in a region of the surface of at least one transducer 22 that produces sound waves in the transducer, which generate negative peak 161. The negative peak begins at a time t₀ substantially simultaneous with a time at which at least one light source 21 transmits the pulse of light 41 which illuminates skin 30.

A second negative peak 162 in signal 152 is generated and begins at a time t\ in response to photoacoustic waves 42 stimulated in skin 30 and in particular in corium 32 as a result of absorption of light 41 by the skin. The photoacoustic waves are generated following a short time delay', i.e. a "release delay", after energy from light 41 is absorbed substantially at time t₀ by skin 30. Time t\ follows time t₀ by a time delay substantially equal to the release delay time and a transmit time delay that is substantially equal to a time it takes sound to travel from the boundary between epidermis 31 and corium 32 to at least one transducer 22. A third negative peak 163 is generated in response to photoacoustic waves 42 stimulated in blood in blood vessel 34 as a result of absorption of light 41 by hemoglobin in the blood and begins at a time t2- Whereas, photoacoustic waves in skin 30 and blood vessel 34 are generated substantially at a same time t₀, time t2 is delayed with respect to time X\ by the release delay and a transmit time of photoacoustic waves from the blood vessel to transducers 22. (Since transducers 22 contact the skin, ti is determined substantially by the release delay and is substantially independent of transit time.) The relatively large positive pulse 64 that follows pulse 163 is generated by at least one transducer 22 in response to decay of pressure from photoacoustic waves 42 that generated pulse 163. Thickness D of the skin is optionally determined responsive to a time difference between negative peaks 162 and 161. Optionally, the time difference is a time delay Δt = (fe- t\) between the onset time of negative peak 163 and the onset time of negative peak 162 and D is determined in accordance with an expression D = Δt c where c is a known speed of sound in skin. D and changes ΔD therein are used to monitor the volume, "Vjsp", and changes ΔVjgp therein of the ISF using known relationships between skin thickness and volume of ISF. Optionally, the relationships between changes in skin thickness and changes in volume of ISF are determined responsive to theoretical and/or empirical studies, for example from studies by C. C. Gyenge, et al noted above and/or, for a particular patient, in a calibration procedure performed on the patient. J. Schumacher et al in "Measurement of Peripheral Tissue Thickness by Ultrasound During The Perioperative Period", British Journal of Anesthesia 82(4); 1999; pp- 641-643 describe experiments showing that changes in thickness of skin on the forehead of a patient due to fluid depletion and fluid replacement during surgery were detectable using ultrasound. In some embodiments of the invention, acoustic transducers 22 are used not only to sense photoacoustic waves but are also used to transmit ultrasound into skin 30 and sense and generate signals responsive to ultrasound waves reflected by features in the skin. The signals generated responsive to the ultrasound reflections are processed to provide measures of thickness of skin 30 and/or its layers and therefrom a glucose assay. For example, a distance at which blood vessel 34 in subcutis 33 or a blood vessel under the subcutis is located below epidermis 31 is determined substantially by the thickness of the dermis 32. Reflections of ultrasound from blood vessel 34 or a blood vessel beneath subcutis 33 are used in accordance with an embodiment of the invention to determine changes in the thickness of dermis 32 and thereby changes in the volume of ISF. Optionally, the ultrasound measures of skin thickness are combined with photoacoustic measures of skin thickness to provide a measure of skin thickness and/or changes therein having improved accuracy.

Fig. 5 shows a graph 80 of skin thickness D determined by a photoacoustic glucometer similar to glucometer 20 in accordance with an embodiment of the invention, as a function of time for an experimental dextrose infusion protocol similar to that for which glucose and HB assays shown in Figs 2A and 2B are acquired. The experiment was conducted with a type II diabetic. Skin thickness measurements acquired during performance of the protocol as a function of time in minutes are indicated by a curve 82 in graph 80. Skin thickness in millimeters (mm) is indicated along a left hand ordinate of the graph. Also shown in graph 80 is a curve 84 indicating measurements of glucose concentration determined during the protocol using a Bayer Glucometer Elite. Values of glucose concentrations indicated by curve 84 are referenced along a right hand ordinate of the graph in mg/dl. Pliotoacoustic measurements of skin thickness provided by the photoacoustic glucometer were calibrated to measurements provided by the Bayer Glucometer during an initial period of the protocol that ended at a time tQ indicated by an indicator line 86. For times greater than tQ, measurements provided by the photoacoustic glucometer are independent of the Bayer Glucometer assays. From the graph it is seen that the skin thickness measurements track and are negatively correlated with changes in blood glucose.

In some embodiments of the invention, changes in skin thickness and Hb assay are correlated to provide an assay of blood glucose and to determine whether the changes in blood volume indicated by assay of a marker are stimulated by a change in glucose levels or from other causes. For example, a temporary decrease in concentration of a marker in the blood may result simply from a patient drinking a large amount of water rather than an increase in blood glucose caused by a medical condition that requires treatment. Whereas a marker assay decrease resulting from an increase in glucose concentration will in general be accompanied by a temporary decrease in ISF volume, imbibition will in general result in a substantially simultaneous increase in both blood volume and ISF volume. The two situations, which both result in an increase in blood volume and decrease in marker concentration are distinguished, in accordance with an embodiment of the invention, by monitoring ISF volume in addition to monitoring blood volume and correlating changes in the volumes. In some embodiments of the invention, ISF volume is monitored at different locations of the body using a plurality of glucometers, optionally similar to glucometer 20, to provide data for correlating changes in ISF volume with changes in blood volume to assay blood glucose. The glucometers are positioned at different locations on the patient's body to provide measures of blood volume and ISF volume at each of the locations. Fig. 6 schematically shows a patient having glucometers 220 for providing photoacoustic measurements of a blood marker and skin thickness mounted to his skin optionally near his ankle and optionally to his upper arm. Optionally, glucometers 220 are similar to glucometers described in US

Provisional application 11/254,550, the disclosure of which is incorporated herein by reference, which are mounted to the skin using suitable stickers and transmit measurement to a processor 222 worn by the patient on his wrist. Glucometers 220 are shown in Fig. 6 as if seen through the patient's clothes.

Correlation of fluid compartment volume changes measured at the different sites is used to indicate if changes in fluid volumes and concomitant changes in concentration of a marker substance are caused by postural changes rather than or in addition to volume changes generated by changes in blood glucose concentrations. For example, assuming the patient gets up from a supine or sitting position, body fluid will tend to pool in the legs causing skin thickness near the ankles to increase and upper arm skin to decrease. However, a major source of the pooled liquid is fluid that leaves the blood, which results in a decrease in blood volume and increase in blood marker concentration. By correlating decrease in upper arm skin thickness with increase in ankle-skin thickness and increase in blood marker concentration, in accordance with an embodiment of the invention, change in the blood marker concentration can be correctly ascribed to change in posture and not to a glucose change that might require medical intervention.

In some embodiments of the invention, a glucometer similar to glucometer 20 is used together with at least one device for determining body posture, for example at least one accelerometer, mounted to a patient's body to aid in recognizing changes in the patient's body posture. Optionally, if the device is at lest one accelerometer, the at least one accelerometer is comprised in the glucometer or a component thereof. Methods of monitoring body posture using accelerometers are described in US Patent 6,834,436, the disclosure of which is incorporated herein by reference. Theoretical models of how body fluid volumes change as a function of posture and/or empirical models of fluid volume change as a function of posture change are used to adjust glucose assays provided by the glucometer and/or marker assays used to provide the glucose assays The inventors have carried out experiments to determine how posture change can affect Hb concentration in the blood. Fig. 7 shows a graph 90 of results from one of the experiments.

In the experiment, a person lay on a tilt bed that was controlled to periodically, relatively rapidly, tilt from the horizontal to an angle of 60° from the horizontal, remain at the 60° angle for about a half hour and then rapidly tilt back to the horizontal. A curve 92 in graph 90 shows three tilt cycles 93 as a function of time shown in minutes along the graph's abscissa. Angle of tilt is shown on an ordinate axis 94 on the right side of the graph. Hb blood concentration as measured using a Hemocue hemoglobin system during the tilt cycles is shown by a curve 100 with Hb concentration values given along an ordinate axis 96 on the left side of graph 90. As expected, Hb concentration shows an increase as body fluid leaves the blood and pools in the lower extremities when the person is tilted up to 60° and decreases when body fluid reenters the blood when the person is tilted back to the horizontal position. The change in Hb concentration exhibits a substantially same rise and fall time for each tilt cycle.

In accordance with an embodiment of the invention, changes in a person's blood marker concentration as a function of changes in posture are experimentally calibrated, optionally in experiments on the patient similar to those that provided the results shown in Fig. 7 and the calibration results used to correct blood glucose assays provided by glucometer 20. Optionally, experiments carried out on various populations are used to acquire data that correlates blood marker concentration changes with postural changes and the data used by glucometer 20 in providing glucose assays. It is expected that the correlations will be functions of inter alia one or more of a person's gender, age and health.

Glucose is of course not the only osmolyte that affects body fluid volumes and the inventors have determined that to provide reliable blood glucose assays it is advantageous to monitor electrolyte concentrations in the extracellular fluid (ECF) and to correct glucose assays provided by a glucometer such as glucometer 20 responsive to changes in electrolyte concentration in the ECF.

Generally, changes in concentration of electrolytes, such as Na⁺, Cl" in the ECF exhibit changes similar to those exhibited by Hb blood concentration and electrolyte concentration changes track, and are positively correlated with, changes in Hb blood concentration. As long as electrolyte and Hb concentration are substantially positively correlated, both concentrations are "passive" respondents to changes generated by a same cause or causes, for example by blood glucose changes. For such situations, changes in either Hb concentration or electrolyte concentration are relatively reliable indicators of changes in glucose concentration. For situations in which changes in electrolyte concentration are not similar to and are not positively correlated with changes in Hb concentration, the inventors have determined that it is advantageous to correct glucose assays provided responsive to marker concentrations and/or skin thickness for changes in electrolyte concentrations. In an embodiment of the invention, electrolyte concentrations are determined responsive to impedance measurements of the body. Any of various methods and apparatus known in the art, for example methods and apparatus described in: PCT Publications WO

02/069791, WO 01/2653; US Patents US 4,765,179, US 5,508,203, US 6,841,389; and/or US applications 20020193673 and 20040193031; may be used for measuring body impedance.

All the documents cited in the preceding sentence are incorporated herein by reference.

Optionally, each glucometer 220 shown mounted to the patient in Fig. 6 comprises at least one electrode attached to the body for use in acquiring impedance measurements. Optionally at least one of the glucometers comprises a power source for generating a current through the body to acquire the measurements.

In the description and claims of the present application, each of the verbs, "comprise" "include" and "have", and conjugates thereof, are used to indicate that the object or objects of the verb are not necessarily a complete listing of members, components, elements or parts of the subject or subjects of the verb. The present invention has been described using detailed descriptions of embodiments thereof that are provided by way of example and are not intended to limit the scope of the invention. The described embodiments comprise different features, not all of which are required in all embodiments of the invention. Some embodiments of the present invention utilize only some of the features or possible combinations of the features. Variations of embodiments of the present invention that are described and embodiments of the present invention comprising different combinations of features noted in the described embodiments will occur to persons of the art. The scope of the invention is limited only by the following claims.

Claims

1. A method of monitoring changes in blood glucose level of a patient comprising: illuminating at least one region of the skin with light that stimulates photoacoustic waves in a marker substance in the blood; and using the photoacoustic waves to measure changes in blood glucose.

2. A method according to claim 1 and comprising illuminating the at least one region of the skin with light that stimulates photoacoustic waves in the skin and using the photoacoustic waves stimulated in the at least one skin region to measure changes in blood glucose

3. A method of monitoring changes in blood glucose level by monitoring changes in volumes of at least one fluid compartment of a body comprising: illuminating at least one region of the skin with light that stimulates photoacoustic waves in the skin and in a marker substance in the blood; and using the photoacoustic waves originating in the blood and in the at least one region of the skin to measure changes blood glucose.

4. A method according to claim 2 or claim 3 wherein using photoacoustic waves stimulated in the at least one region of skin comprises using the waves to determine a change in volume of ISF fluid in the skin.

5. A method according to claim 4 wherein using the waves to determine a change in the ISF volume comprises using the waves to determine change in thickness of the at least one region of the skin and/or a layer thereof.

6. A method according to any of the preceding claims and comprising illuminating a blood vessel below the at least one region of the skin with light that stimulates photoacoustic waves in the blood vessel and using the waves to measure changes in blood glucose.

7. A method according to claim 6 wherein using the photoacoustic waves stimulated in the blood vessel below the skin comprises using the waves to determine change in thickness of the at least one region of the skin.

8. A method according to claim 7 and comprising using the change in skin thickness to determine change in volume of ISF fluid in the at least one region of the skin.

9. A method according to any of claims 1-8 wherein using photoacoustic waves stimulated in the marker comprises using the waves to determine a change in volume of the blood.

10. A method according to claim 9 wherein using the photoacoustic waves stimulated in the marker comprises using the waves to assay the marker in the fluid compartment.

11. A method according to any of the preceding claims wherein the marker is at least one of hemoglobin (Hb), red blood cell count (RBC), or packed red cell volume (PCV).

12. A method according to any of the preceding claims and comprising transmitting ultrasound into the skin and using reflections of the ultrasound from a feature in or below the skin to measure changes in glucose.

13. A method according to claim 12 wherein using the reflections to determine change in thickness of the skin.

14. A method according to claim 13 and comprising using the skin thickness change to determine change in volume of ISF fluid in the skin.

15. A method according to any of claims 12-14 wherein the feature is a blood vessel.

16. A method according to any of the preceding claims wherein the at least one region of the skin comprises a plurality of regions.

17. A method according to claim 16 and comprising using the photoacoustic waves from different skin regions to measure changes in blood glucose.

18. A method according to claim 16 or claim 17 wherein the photoacoustic waves from different regions comprises using the waves to adjust the measured change in blood glucose for changes in the patient's posture.

19. A method of monitoring changes in blood glucose level of a patient comprising: illuminating at least one region of the skin with light that stimulates photoacoustic waves in the body; using the photoacoustic waves to provide signals responsive to changes in a plurality of fluid volumes in the body; and using the signals to determine changes in blood glucose.

20. A method of according to claim 19 wherein the plurality of fluid volumes comprises the blood.

21. A method according to claim 19 or claim 20 wherein the the plurality of fluid volumes comprises the interstitial fluid.

22. A method according to any of claims 19-21 wherein the at least one skin region comprises a plurality of different skin regions.

23. A method according to any of the preceding claims and comprising acquiring impedance measurements of the body and using the impedance measurements to determine changes in blood glucose.