Non-invasive tissue glucose level monitoring

Instruments and methods for performing non-invasive measurements of analyte concentrations and for monitoring, analyzing and regulating tissue status, such as tissue glucose levels.

 

We claim:

1. A nocturnal glucose monitor, comprising:

a non-invasive glucose measurement probe for detecting glucose levels of a juvenile patient,

an alarm unit responsive to the glucose measurement probe, the alarm unit being operative to detect excursions of glucose values outside of a predetermined juvenile nocturnal glucose range for a diabetic patient and to produce a parental alarm signal in response to detected excursions,

an audio transducer responsive to the alarm signal, and

a remote transmitter responsive to the non-invasive glucose measurement probe and a receiver responsive to the remote transmitter, wherein the audio transducer is responsive to the remote transmitter.

2. The nocturnal glucose monitor of claim 1 wherein the remote transmitter is a wireless transmitter and the receiver is a wireless receiver.

3. The nocturnal glucose monitor of claim 2 wherein the glucose measurement probe is a fluorescence-based probe.

4. The nocturnal glucose monitor of claim 1 wherein the glucose measurement probe is a fluorescence-based probe.

5. A nocturnal glucose monitoring method, comprising:

providing a non-invasive glucose measurement probe such that it is responsive to a glucose level of a child during nighttime sleep,

detecting excursions of glucose values outside of a predetermined nocturnal glucose range for a diabetic child during nighttime sleep of the child, and

causing a remote receiver to issue an audible alarm to a parent of the child in response to the step of detecting.

6. The method of claim 5 wherein the step of causing operates based on wireless transmission.

7. The method of claim 6 wherein the step of detecting operates based on fluorescence.

8. The method of claim 5 wherein the step of detecting operates based on fluorescence.

FIELD OF THE INVENTION

This invention relates to instruments and methods for performing non-invasive measurements of analyte concentrations and for monitoring, analyzing and regulating tissue status, such as tissue glucose levels.

BACKGROUND OF THE INVENTION

Diabetes is a chronic life threatening disease for which there is presently no cure. It is the fourth leading cause of death by disease in the U.S. and at least 90 million people worldwide are estimated to be diabetic. Diabetes is a disease in which the body does not properly produce or respond to insulin. The high glucose levels that can result from this affliction can cause severe damage to vital organs, such as the heart, eyes and kidneys.

Type I diabetes juvenile diabetes or insulin-dependent diabetes mellitus) is the most severe form of the disease comprising approximately 10% of the diabetes cases in the United States. Type I diabetics must receive daily injections of insulin in order to sustain life. Type II diabetes, (adult onset diabetes or non-insulin dependent diabetes mellitus) comprises the other 90% of the diabetes cases. Type II diabetes is often manageable with dietary modifications and physical exercise, but may still require treatment with insulin or other medications. Because the management of glucose to near normal levels can prevent the onset and the progression of complications of diabetes, persons afflicted with either form of the disease are instructed to monitor their blood glucose level in order to assure that the appropriate level is achieved and maintained.

Traditional methods of monitoring the blood glucose level of an individual require that blood be withdrawn. This method is painful, inconvenient, costly and poses the risk of infection. Another glucose measuring method involves urine analysis, which, aside from being inconvenient, may not reflect the current status of the patient's blood glucose because glucose appears in the urine only after a significant period of elevated levels of blood glucose. An additional inconvenience of these traditional methods is that they require testing supplies such as collection receptacles, syringes, glucose measuring devices and test kits. Although disposable supplies have been developed, they are costly and can require special methods for disposal.

Many attempts have been made to develop a painless, non-invasive external device to monitor glucose levels. Various approaches have included electrochemical and spectroscopic technologies, such as near-infrared spectroscopy and Raman Spectroscopy. Despite extensive efforts, however, none of these methods appears to have yielded a non-invasive device or method for the in vivo measurement of glucose that is sufficiently accurate, reliable, convenient and cost-effective for routine use.

SUMMARY OF THE INVENTION

The invention overcomes problems and disadvantages associated with current strategies and designs and provides new instruments and methods for monitoring, analyzing and regulating in vivo glucose levels or other analyte levels in an individual.

In one general aspect, the invention features a non-invasive glucose monitoring instrument useful in vivo. The instrument may comprise a radiation source capable of directing radiation to a portion of the exterior or interior surface of a patient. That surface may be a mucosal area such as the gums and other mucosal areas, the eyeballs and surrounding areas such as the eyelids and, preferably, the skin. The source emits radiation at a wavelength that excites a target within the patient such that the excited target provides a glucose level indication of the patient. A glucose level indication is a quantitative or relative measurement that correlates with the blood glucose content or concentration of the patient. The instrument may further comprise a radiation detector positioned to receive radiation emitted from the excited target, and a processing circuit operatively connected to the radiation detector that translates emitted radiation to a measurable signal to obtain the glucose level indication. The target is not glucose itself, but a molecular component of the patient such as, for example, a component of skin or other tissue, that reflects or is sensitive to glucose concentration, such as tryptophan or collagen cross-links. Suitable targets are structural components, and compounds and molecules that reflect alterations in the environment of matrix components of the tissue and are sensitive to or correlate with tissue glucose concentration. The target provides an emitted fluorescence signal that is related to the patient's blood glucose level. The radiation detector is responsive to the emission band of the target or species in the skin. Preferably the radiation is ultraviolet radiation or light. The emitted radiation is preferably fluorescence radiation from the excitation of the non-glucose target. The instrument may further include means for measuring scattering re-emitted from the irradiated skin. The radiation emitted from the excited target and signal therefrom correlates with the blood glucose of the patient.

Another aspect of the invention relates to an instrument for assessing changes in the superficial structural matrix of the skin or other tissue of a patient comprising means for measuring fluorescence, and means for measuring scattering.

Another aspect of the invention relates to an instrument for assessing changes in the environment of matrix components of the skin or other tissue of a patient comprising means for measuring fluorescence, and means for measuring scattering. Preferred embodiments further include means for combining signals from the means for measuring fluorescence and the means for measuring scattering.

Another aspect of the invention relates to a non-invasive method of detecting or assessing a glucose level comprising exciting a target that, in an excited state, is indicative of the glucose level of a patient, detecting the amount of radiation emitted by the target, and determining the glucose level of the patient from the amount of radiation detected. The target is preferably a molecular species in the skin. Preferred targets are tryptophan or a matrix target, like PDCCL, which are excited by ultraviolet radiation and act as bioamplifiers or bioreporters. Targets may be structural matrix or cellular components. Suitable targets reflect alterations within the environment of matrix components of the skin or other tissue and act as bioamplifiers or bioreporters when excited with ultraviolet radiation.

Still another aspect of the invention relates to a non-invasive method of assessing a change in the superficial structural matrix of a tissue, or a change in the environment of matrix components, comprising exposing the tissue to radiation at a first wavelength, detecting an amount of fluorescence emitted by exposed tissue, exposing the tissue to radiation of a second wavelength, detecting an amount of scattering re-emitted from the exposed tissue, and deriving an indication representative of the change in the superficial structural matrix of the tissue, or a change in tissue matrix components or their environment, based on of the amount of fluorescence detected and the amount of scattering detected.

Other objects and advantages of the invention are set forth in part in the description which follows, and in part, will be obvious from this description, or may be learned from the practice of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 A multipurpose skin spectrometer that provides data specifically relevant to signals correlating with blood glucose.

FIG. 2 Block diagram of one embodiment of a glucose level monitoring instrument.

FIG. 3 Graph of the average fluorescence excitation spectra for normal and diabetic SKH mice for an emission wavelength of 380 nm.

FIG. 4 Graph of the average fluorescence excitation spectra for normal and diabetic SKH mice for an emission wavelength of 340 nm.

FIG. 5 Graph of the average fluorescence excitation spectra for a rat at an emission wavelength of 380 taken at different blood glucose levels.

FIG. 6 Plot of the fluorescence intensity at 346 nm for four different glucose levels which are taken from FIG. 5.

FIG. 7 Graph of the average fluorescence excitation spectra for an emission wavelength of 380 nm for a human male before and after the ingestion of 100 grams of glucose.

FIG. 8 Graph of the average fluorescence excitation spectra for an emission wavelength of 380 nm for a human male before and after the ingestion of 100 grams of glucose.

FIG. 9 Graph of the average fluorescence excitation spectra for an emission wavelength of 380 nm for a human female before and after the ingestion of 100 grams of glucose.

FIG. 10A A diagram depicting collection of fluorescence spectra with components attributable to tryptophan and collagen cross links following irradiation with UV light.

FIG. 10B A diagram depicting scattering according to a scattering model.

FIG. 11 Block diagram of a monitoring instrument that can be used to monitor tissue glucose levels or evaluate changes in the superficial structural matrix of a tissue or the environment of matrix components of a tissue.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

As embodied and broadly described herein, the present invention relates to devices and methods for quantitating, trending and/or reporting an analyte, such as blood glucose, to devices and methods for monitoring and regulating in vivo glucose levels, and to devices and methods for evaluating the superficial structural matrix or cellular components of a tissue.

It has been discovered that by measuring fluorescence following irradiation of a tissue surface of a patient, such as the patient's skin, and by optionally assessing scattering, the glucose level of a patient can be evaluated. Evaluation according to the invention is based on the surprising discovery that the quantum efficiency of fluorescence of a responsive target within the skin is transiently affected by the irradiation and can be correlated to the ambient glucose content. Long-term interaction between diabetes, collagen and other species has been previously observed (V. M. Monnier et al., Diabetes 37:867-872, 1988). However, a reversible component of this interaction that correlates with blood glucose levels and possibly depends on the glucose level in the environment of collagen and other targets has previously gone unnoticed. More specifically, although glucose itself does not fluoresce to any significant degree, when the blood glucose level of a patient changes, the quantum efficiency of fluorescence of a target such as, for example, pepsin-digestible collagen cross links (PDCCL), also changes. This change may be due, in part, to the direct and indirect effects of the relative presence of glucose or other molecules on the environment of target molecules and structures. That presence induces a reversible change in the quantum efficiency of fluorescence production by the target which can be detected and analyzed. Glucose molecules in the environment may be covalently or noncovalently coupled to the target (glycosylated collagen), or simply free in the immediate vicinity of the target. Targets may be in the dermal matrix, in the epidermal matrix, or in cells or the immediate vicinity of cells associated with the either the dermis or the epidermis. In this regard, the invention may also be used to directly assess the amount or degree of advanced glycation end products that exist in an area of the body such as, for example, in vessels, arteries or organs.

A fluorescent signal originating from dermal collagen cross links has been identified, which signal slowly increases with aging and is also sensitive to transient exposure to ultraviolet radiation. PDCCL fluoresces following excitation at 335-340 nm, with the emission maximum at 390 nm (N. Kollias et al., Journal of Investigative Dermatology, 111:776-81 1998). The fluorescent signal decreases monotonically with a single UV exposure, but recovers within hours. With multiple exposures, the effects appear cumulative, and recovery takes weeks. However, it has been discovered that transient changes in the environment of these collagen cross links causes significant and transient alterations in their fluorescence which can be tightly correlated with blood glucose determinations.

Targets in the environment of matrix components, such as collagen cross links serve as bioamplifiers or bioreporters of ambient glucose concentrations and, thus, constitute a novel and sensitive means of non-invasively assessing glucose in real time. Advantages of this methodology include a large change in signal level for a relatively small change in collagen structure or matrix environment. The method is also unhampered by absorption from competing species in the general area. In addition, there are only a few fluorophores which makes signal analysis easier. Further, detector sensitivity is generally excellent and instrumentation and optical components, all of which are commercially available, are potentially simpler and less expensive than those used for infrared measurements. Also, given the robust signals and signal to noise ratios observed, there is potentially less of a need to resort to complex algorithmic and chemometric analyses.

Accordingly, one aspect of the present invention is related to a non-invasive in vivo glucose monitoring instrument that determines glucose levels or changes in glucose levels by measuring fluorescence of the skin following excitation of one of these targets or species. Specifically, fluorescence signals obtained following irradiation of skin or other tissue can be correlated with glucose levels, or changes in glucose levels, by measuring fluorescence following excitation of targets or species within the environment of the matrix components. Preferred targets are structural matrix components such as PDCCL. Another preferred target is epidermal tryptophan which, like other targets, may be bound to other compounds or structures, and intracellularly or extracellularly localized. Other useful matrix targets for excitation include collagenase-digestible cross links, elastin cross links, glycosaminoglycans, glycated collagen and glycosylated substances in a tissue. These targets may also be referred to as biosensors as they are biological substances that detectably change in response to glucose content, or bioamplifiers as they may amplify a signal indicative of systemic glucose levels.

A non-invasive glucose monitoring instrument according to one aspect of the invention includes a radiation source capable of directing radiation to a portion of the surface of the skin (or other tissue) of a patient. The source emits radiation at a wavelength that excites a target of species in the tissue that can be correlated with blood glucose content, such that the excited target provides a glucose level indication of the patient. In a preferred embodiment, the target is a molecule other than glucose, and most preferably is a structural matrix component such as, for example, collagen cross-links. Alternatively, the target may be tryptophan. When the target being detected is cross-linked collagen, the ultraviolet radiation source is preferably operative to irradiate at approximately 330-345 nanometers, and the ultraviolet detector is sensitive to emitted wavelengths in the range of 370-410 nanometers, more preferably, 380-400 nanometers and, most preferably, 390 nanometers. As noted, another useful target whose change in emission may be detectable is tryptophan. When the target being detected is tryptophan, the ultraviolet radiation source is preferably operative to irradiate at approximately 285-305 nanometers, more preferably at approximately 295 nanometers, and the ultraviolet detector is preferably sensitive to emitted wavelengths in the range of 315-420 nanometers, more preferably 340-360 nanometers, and most preferably, 345 nanometers. The radiation emitted by the target correlates with the glucose level of the patient. The spectral information can be converted into a number correlative to standard blood glucose determinations.

The instrument further comprises a radiation detector positioned to receive radiation emitted from an excited target. The instrument further includes a processing circuit operatively connected to the radiation detector and operative to translate a level of emitted radiation into a measurable signal that is representative of or may be correlated with the blood glucose level. Preferably, the radiation source is ultraviolet light. In a preferred embodiment the radiation source may comprise a flexible-fiber optic arm or probe that directs said radiation to the target. The probe may comprise a glass or quartz fiber and may be flexible and easily manipulated to examine a site anywhere on the patient's skin. The portion of skin irradiated may be less than about 1 square cm, and more preferably is about 0.2 square cm. Preferably, the portion is a site which is most easily measurable on the patient such as on the arm or leg. Differences in pigmentation between different areas of the body as well as different patients can be factored or eliminated through selection of control input, and overcome.

The instrument may further comprise a display such as, for example, a visual, auditory or sensory display operatively connected to the processing circuit and operative to display the glucose level indication. Optionally, this data may be analyzed and transmitted to a pump or other servo mechanism responsive to the processing circuit. The pump is incorporated into the system such that the pump administers insulin or other medication to the patient at a rate that corresponds to the glucose level signal.

Referring to FIG. 1, an embodiment of the glucose monitor of the invention includes a Xenon arc (Xe-arc) lamp, double excitation and emission monochromators, a photomultiplier device, a simple current amplifier and a flexible probe. The probe may comprise fiber optic bundles which allow convenient evaluation of living systems. This embodiment can take the form of a multipurpose skin spectrometer or it may be modified to create a unit optimized to provide data specifically relevant to signals correlating with blood glucose. One advantage of utilizing fluorescent excitation spectra compared to fluorescence emission spectra is that the former are similar to absorption spectra, which aids in the separation and identification of the individual fluorophores in a complex spectrum. Although other components can be substituted for the elements in this embodiment, a Xe-arc in combination with an excitation monochromator, avoids the major constraint of laser sources, namely the limited number of excitation wavelengths.

Optionally, other types of sources, such as a diode laser, coupled with enhanced spectral analysis algorithms optimized for the collagen cross links may be used. These algorithms may also incorporate variables such as skin type, age, exposure, etc., all of which are analyzed during testing. Hardware modifications and calibrations may be incorporated to take into account these and other variables. Specific algorithms and software may be embedded into a dedicated processor. For example, one design may comprise a night hypo/hyperglycemia monitoring instrument which is programmed to alarm by trending analysis parameters that correlate with significant changes in blood glucose. Alternatively, monitoring could be performed with a transportable fiber-based fluorescence spectrophotometer with double monochromators, both on the excitation and emission paths. This allows the evaluation of different subsets of collagen cross links and tryptophan signals as well as allowing the estimation of epidermal melanin pigmentation or other tissue pigments. Optimized instruments may duplicate and incorporate the functionality and data processing requirements incorporated from appropriate studies.

Another embodiment uses a fiber-based fluorescence spectrometer with two double monochromators and a high intensity excitation light source (350 W Xe-arc). The double monochromator design minimizes stray light, which tends to be high because of the high level of light scattering by the tissues. The probe is preferably a fiber optic device that allows collection of data from different skin sites on the body. Probe design is optimized to permit ease of use and reproducibility. Optimization of light sources, filters and software can be designed to perform three scans that maximize the collagen fluorescence signals. One scan is preferably 250-360 nm on the excitation band and 380 nm on the emission. The second scan is preferably 250-400 nm on the excitation and 420 nm on the emission. The third scan is preferably 360-480 nm on the excitation and 500 nm on the emission. This provides information on PDCCL (340/390 nm), the collagenase digestible collagen crosslinks (370/460 nm) and the collagen/elastin crosslinks (420/500 nm), among other species. The system may also provide data on tryptophan, an epidermal fluorophore having an excitation wavelength of 290-300 nm and an emission wavelength of 340-360 nm, among other species. Devices may be small and lightweight desktop units useful in health care provider settings. A remote probe may be connected to the system through a flexible fiber optic bundle. Data output may consist of a reporting of a quantitative number that correlates with blood glucose readings, along with spectral data, which may be displayed on a separate small I/O terminal or laptop computer. The software further contains diagnostic overlay capabilities.

Another device allows monitoring of glucose levels, by providing spectral information reflective of glucose levels, on a continuous or repetitive basis. In one embodiment, this would be used throughout the night with a built-in alarm, to alert the patient to abnormal decreases or increases in glucose levels. The unit, which may be the size of a clock radio, can have a fiber optic cable to connect to the patient, similar to existing apnea monitors and pulse oxymeters. Another portable device may be placed in contact with the skin for periodic momentary glucose readings. It may have an LCD readout for glucose levels, memory to store several hundred glucose readings and a data output to download stored data.

An alarm may be operationally coupled to the processing circuit such that the alarm is activated when the glucose level indication exceeds a first predetermined value (such as 200 gm/l), falls below a second predetermined value (such as 70 gm/ml), or varies more than 20% from a third predetermined value (such as the previously measured level or a baseline level determined for the patient). Alternately, the alarm may be triggered in response to a more complex algorithmic analysis of data or based on evaluation by trending analysis over time.

The instrument may further comprise a normalizing detector responsive to another target in the tissue, such that the processing circuit is responsive to the normalizing detector to normalize the glucose level indication. For example, a current or latest glucose level signal may be normalized by comparing it to a previously determined glucose level signal which has been calibrated by comparing it directly with a conventionally determined blood glucose level. Alternatively, normalization may involve comparison of emissions from the same target but at another wavelength, comparison of emissions from a non-target such as glucose or another structural or circulating component of the body, or simply taking a reading from another skin site. Normalization may also be performed by comparison to similar data from another point or points in time taken from the same individual, or utilizing a stored database or spectral library. Normalizing may alternately comprise obtaining a baseline signal before any prolonged activity where continual measurements would be difficult such as, for example, before driving or sleeping, and watching for changes or trends of changes. The previously determined glucose level signal may also be compared with a level assessed from a simultaneously drawn blood sample. In addition, scattering evaluation may be factored into the normalizing process.

The instrument may optionally comprise means for measuring scattering re-emitted from the tissue. As discussed below, the means for measuring scattering may comprise a skin illuminating means that emits radiation at an angle greater than 60 degrees to said target or it may comprise a skin or tissue illuminating means which emits radiation at between about 330 to 420 nm. Re-emitted radiation is then collected and analyzed.

The instrument may include a portable housing in which the radiation source, the radiation detector and the processing circuit are disposed. The instrument may include a battery compartment disposed in the housing and a pair of battery contacts operatively connected to the ultraviolet radiation source, the ultraviolet radiation detector, and the processor. Data can be electronically recorded, stored or downloaded for later review or analysis. The instrument may further comprise attachment means for attaching the radiation source, a portion of, or all of the device to the patient. The portable housing, the ultraviolet radiation source, the ultraviolet radiation detector, and the processor may be designed so that they weigh in combination less than 3 kilograms, more preferably less than 1 kilogram, and most preferably, less than 0.5 kilograms. The instrument may optionally include an attachment mechanism for attaching the housing to the patient. Alternately, the instrument can be miniaturized; in such an embodiment, a microprocessor is incorporated onto a dermal patch, which may be operatively connected to other devices that provide input directly to a pump or other biodelivery system, such as a transmucosal or inhalational system, which may deliver insulin or other appropriate medication to the patient.

The instrument may also be constructed using small components composed of inexpensive, possibly recyclable materials such as plastics and paper, so that the entire instrument or a significant portion is disposable. For example, the entire device can be incorporated into a patch worn anywhere on the body and secured with adhesive tape, hook-and-loop fastener or another suitable means. After expiration or depletion of an integral battery, the patch can be safely and easily disposed of and a new patch secured. Such instruments weigh less than 1 kg, preferably less than 0.5 kg and more preferably less than 0.1 kg.

The processing circuit is preferably operative to translate the level of detected radiation into a measurable glucose level signal that is indicative of the glucose level in the tissue. The signal may be directly evaluated, or it may be compared to stored reference profiles, to provide an indication of changes from previous levels or trends in the patient's glucose level. Although a preferred embodiment measures radiation or fluorescence following irradiation of the skin, the present invention can also be used to assess glucose levels by evaluation of other tissues. For instance, glucose levels may be assessed in accordance with the present invention by detecting radiation or fluorescence following irradiation of the surface of other tissues, such as mucous membranes, or irradiation of the mucosa, submucosa or serosa of any organ.

Another aspect of the invention relates to a non-invasive method of detecting a glucose concentration or level in vivo comprising the steps of exciting a target in the skin or other tissue, preferably using ultraviolet radiation, that is sensitive to the patient's tissue glucose content and is indicative of the glucose level of the patient, detecting an amount of radiation or fluorescence emitted by the target, and deriving an indication representative of or which correlates with a current blood glucose level based on the amount of radiation or fluorescence detected. Preferably, the target is a matrix target such as collagen cross links. Alternatively, the target may be tryptophan. The method may optionally include the step of determining whether to take steps to adjust the patient's glucose level in response to the derived glucose level, followed by the step of administering insulin or another pharmaceutical composition in response thereto. The method may include any one or more of the steps of reporting the information to the patient, recommending a dosage, or administering the composition, such as insulin, to the patient in response to the indication derived. The step of administering may be performed by using a syringe, a pump or another suitable biodelivery system, mechanical or chemical, which may be implanted or external to the body. The method may also include the step of displaying a glucose level indication related to the indication derived or providing a warning to the patient. The method may further include the step of normalizing the glucose level indication derived in the step of deriving. The steps of exciting, detecting, and deriving may be performed continuously or at any appropriate interval, for example, by the minute, hourly, daily or every other day for the same patient and over a period of days, weeks, months or years.

Optionally, the method may include actuating an alarm in response to the glucose level when the glucose level exceeds a predetermined first level, falls below a predetermined second level or varies more than a set percentage, such as for example, 10%, 20%, 30%, 50% or 100% or more from a predetermined third level or changes in such a way that meets criteria of a specifically designed algorithm. The method may further comprise the step of measuring scattering re-emitted from the skin or irradiated tissue surface and utilizing the resulting data to initiate or assist in actuating a process aimed at adjusting the