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  Method and apparatus for non-invasive monitoring of blood substances using self-sampled tearsUSPTO Application #: 20070043283Title: Method and apparatus for non-invasive monitoring of blood substances using self-sampled tears Abstract: A method and apparatus for non-invasively determining the concentration of a substance in blood, such as glucose, include a sample portion arranged for contacting an eye region of a user to obtain a tear fluid sample, a sensor in communication with the sample portion for generating a signal related to the tear substance concentration, and a processor in communication with the sensor for determining a blood substance concentration corresponding to the tear substance concentration. (end of abstract)
Agent: Brooks Kushman P.C. - Southfield, MI, US Inventors: Bruce E. Cohan, Geun Sig Cha, Mark E. Meyerhoff, Hakhyun Nam, Donald E. Gillespie, Gang Cui, Jong Sik Kim, Zvi Flanders USPTO Applicaton #: 20070043283 - Class: 600345000 (USPTO) Related Patent Categories: Surgery, Diagnostic Testing, Measuring Or Detecting Nonradioactive Constituent Of Body Liquid By Means Placed Against Or In Body Throughout Test, Electroanalysis The Patent Description & Claims data below is from USPTO Patent Application 20070043283. Brief Patent Description - Full Patent Description - Patent Application Claims
CROSS-REFERENCE TO RELATED APPLICATIONS [0001] This application is a continuation of U.S. application Ser. No. 10/404,702 filed Apr. 1, 2003 which, in turn, claims the benefit of U.S. provisional application Ser. No. 60/370,552 filed Apr. 5, 2002. BACKGROUND OF THE INVENTION [0002] 1. Field of the Invention [0003] This invention relates to a method and apparatus for non-invasive monitoring of blood substances, particularly glucose, using self-sampled tears. [0004] 2. Background Art [0005] The measurement of glucose in blood plasma is perhaps the most important physiologic analyte measurement in medicine, as diabetes has immense public health implications. Diabetes is a leading cause of disability and death, affecting approximately seventeen million Americans. The total annual cost of treating diabetes and its complications in the United States is in excess of $150 billion, a large part of the total national expenditure for health care. [0006] The medical management of diabetes by tight glycemic (blood glucose) control can minimize its devastating kidney, ocular, neurological, and vascular complications, as documented in the National Institutes of Health-sponsored Diabetes Control and Complications Trial. However, the trial resulted in a three-fold increase in hypoglycemic incidents. Of great concern to diabetologists in their care of these patients is hypoglycemia awareness because of its serious risk for morbidity and mortality. [0007] Tight glycemic control requires frequent measurement by the patient of his/her blood glucose levels, which typically requires a "finger stick" to obtain a blood sample up to eight times daily. This procedure is painful and inconvenient for even the most compliant patients, such that limited patient compliance with self-testing is a significant problem in the medical management of this disease. Accordingly, the need for a non-invasive approach to diabetes management is universally recognized to achieve the goal of involving patients in a proactive way in their glycemic control, both in monitoring blood glucose and in insulin delivery. [0008] The tremendous need for a reliable, cost-effective method of non-invasive blood glucose measurement for diabetes management has stimulated hundreds of analytic approaches. The invasiveness of these approaches extends from implanted sensors through a range of less, to minimally, to non-invasive methods. Minimally invasive methods include chemical or spectroscopic measurement of interstitial fluid from the skin obtained by reverse iontophoretic, electroosmotic, or thermal microporation sampling. Among the other technologically sophisticated approaches to glucose measurement are spectroscopy (transcutaneous infrared, fluorescence lifetime, pulsed laser photoacoustic, and far infrared), analysis of breath, optical measurements of the aqueous humor of the eye, polarimetry, and radio wave impedance. Some of these methods have worked well in controlled laboratory testing, but in practice other chemical species, tissue optics, variations in temperature, and other factors have confounded the measurement. For all spectroscopic approaches, the major problem is the need for frequent calibration, as infrared absorption bands for various chemicals in blood or interstitial fluid can overlap significantly and are influenced by temperature and hydrogen bonding effects. [0009] The concentration of low molecular weight analytes, like glucose, in blood plasma is correlated with the levels found in lacrimal fluid, or tears. While a number of methods for measuring this analyte have been applied to tears, two main factors have prevented the practical use of measuring tear glucose concentration as a means for self-monitoring blood glucose concentration: 1) the low level of glucose in tears, reported in a recent study (see Chen et al., J Cap Elec 1996; 5:243-248) to be approximately 1/25 the level in blood, and 2) the small volume of tear fluid as compared with blood that is readily available for analysis. In the aforementioned Chen study, glucose concentration in microliter samples of human tears obtained with capillary tubes was determined by capillary electrophoresis (CE) with laser-induced fluorescence (LIF), a sophisticated method limited to research chemistry laboratories because of its technical complexity. [0010] Currently, no practical, entirely non-invasive system and method exists for patients to self-monitor their blood glucose with the level of accuracy and responsiveness required. SUMMARY OF THE INVENTION [0011] Therefore, it is an object according to the present invention to provide a method and apparatus for determining the concentration of a substance in tears which will allow for indirect monitoring of the substance concentration in blood. [0012] It is a further object according to the present invention to provide an improved method and apparatus for non-invasively determining blood glucose concentration in a simple and accurate manner. [0013] It is a still further object according to the present invention to provide a method and apparatus for determining glucose concentration in tear fluid that is self-sampled by a patient. [0014] Accordingly, a method is provided for determining the concentration of a substance in blood, such as glucose, where the method includes providing a test apparatus having a sample inlet, and engaging an eye region of a user with the sample inlet to obtain a tear fluid sample. The method further includes processing the tear fluid sample using the test apparatus to determine a tear substance concentration, and correlating the determined tear substance concentration with a blood substance concentration. [0015] Correspondingly, an apparatus for determining the concentration of a substance in blood, such as glucose, is provided which includes a sample portion arranged for contacting an eye region of a user to obtain a tear fluid sample, a sensor in communication with the sample portion for generating a signal related to the tear substance concentration, and a processor in communication with the sensor for determining a blood substance concentration corresponding to the tear substance concentration. [0016] In a preferred embodiment, a user self-samples tear fluid from his/her eye region by engaging a lower lid region and obtaining tear fluid from a tear meniscus. While obtaining the tear fluid sample, the eye may be substantially closed. Advantageously, the tear fluid sample can be less than about 0.5 .mu.L. Preferably, the sample portion, or test probe, includes an inlet that extends outwardly from the test probe, such as a capillary member or a wicking membrane, to facilitate contact with the eye. The sample portion is preferably removable from the apparatus. In a preferred embodiment, the apparatus includes a generally pen-shaped housing. [0017] The sample portion includes an enzyme, preferably glucose dehydrogenase, for reacting with the substance in the tear fluid sample. The sample portion further includes an electron transfer mediator, such as a ruthenium complex. The coenzyme pyrrolo-quinoline-quinone (PQQ) can also be utilized. In a preferred embodiment, the sample portion includes a base plate, a cover plate, and a spacer disposed between and joining the base and cover plates, where the base and cover plates include a converse-type electrode system. A power supply is provided for applying a voltage to the electrode system to induce an electrochemical reaction of the enzyme and the electron transfer mediator with the substance in the tear fluid sample and generate a current related to the tear substance concentration. The processor then determines a tear glucose concentration from the generated current and multiplies the tear glucose concentration by a calibration factor to determine the corresponding blood glucose concentration. An amplifier can be provided for amplifying the generated current, and a speaker can be provided to generate audible indications for the user. Additionally, a display screen is provided in communication with the processor for displaying the blood substance concentration, and memory is provided in communication with the processor for storing the blood substance concentration. [0018] In accordance with the present invention, a method for determining glucose concentration in a sample of tear fluid includes providing a test apparatus having a sample inlet arranged for contacting an eye region of a user, engaging the eye region with the sample inlet to obtain a tear fluid sample, and processing the tear fluid sample using the test apparatus to determine the glucose concentration in the tear fluid sample. Correspondingly, an apparatus for determining glucose concentration in a tear fluid sample includes a sample portion arranged for contacting an eye region of a user to obtain a tear fluid sample, a sensor in communication with the sample portion for generating a signal related to the glucose concentration in the tear fluid sample, and a processor in communication with the sensor for processing the signal to determine the tear glucose concentration. [0019] In further accordance with the present invention, a method for determining blood glucose concentration includes providing a test apparatus including a sample portion which includes an enzyme. The method further includes engaging an eye region of a user with the sample portion to obtain the tear fluid sample, reacting the tear fluid sample with the enzyme to generate a signal related to the tear glucose concentration, processing the signal using the test apparatus to obtain a blood glucose concentration corresponding to the tear glucose concentration, and providing an output indicative of the blood glucose concentration. Correspondingly, an apparatus for determining glucose concentration in blood includes a sample portion having an inlet arranged for contacting an eye region of a user to obtain a tear fluid sample, where the sample portion contains an enzyme for initiating a reaction with the tear fluid sample. A sensor in communication with the sample portion detects a signal generated by the reaction, and a processor in communication with the sensor determines a tear glucose concentration from the detected signal and correlates the determined tear glucose concentration with a blood glucose concentration. The apparatus further includes means for providing an output indicative of the blood glucose concentration. [0020] According to the present invention, a probe is provided for obtaining a tear fluid sample. The probe includes an input end arranged to contact an eye region of a user to obtain the tear fluid sample, and a probe body in communication with the input end and having components for generating a reaction with a substance, such as glucose, in the tear fluid sample. The probe further includes an output end in communication with the probe body and arranged to be removably mated with a test apparatus for determining a concentration of the substance in the tear fluid sample. [0021] In a preferred embodiment, the input end extends outwardly from the probe body, and can include a capillary member or a wicking membrane. The probe body preferably includes an enzyme, such as glucose dehydrogenase, for reacting with the substance in the tear fluid sample, and can also include a coenzyme, such as pyrrolo-quinoline-quinone (PQQ). The probe body preferably further includes an electron transfer mediator, such as a ruthenium complex. The probe body preferably includes a base plate, a cover plate, and a spacer disposed between and joining the base and cover plates, where the base and cover plates include an electrode system. The electrode system is of a converse type, where a working electrode is provided on one of the base and cover plates and a reference electrode is provided on the other of the base and cover plates. Continue reading... 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