Non-invasive blood glucose monitoring
8 technical routes for non-invasive blood glucose monitoring
The glucose in the blood is called blood sugar (Glu). Glucose is an important component of the human body and an important source of energy. Since the source and the way of blood sugar are roughly the same, the production and utilization of blood sugar in normal people are in a dynamic equilibrium state.
The sources of blood sugar include: ① food digestion and absorption; ② decomposition of glycogen stored in the liver; ③ conversion of fat and protein.
The path of blood sugar includes: ① oxidization into energy; ② into glycogen and stored in the liver, kidney and muscle; ③ into fat and protein and other nutrients for storage. The pancreatic islets are the main organs in the body that regulate the blood glucose concentration of blood sugar, and the liver stores glycogen. Blood glucose concentration is also regulated by nerve and endocrine hormones.
Diabetes is a group of metabolic diseases characterized by high blood sugar. Hyperglycemia is caused by defective insulin secretion or impaired biological effects, or both. The IDF Global Diabetes Map (9th edition) shows that the number of diabetic patients worldwide is increasing, with an average global growth rate of 51%. There are currently 463 million diabetic patients. According to the growth trend, it is estimated that there will be 700 million diabetic patients worldwide by 2045. Among them, the number of patients in Africa increased the fastest, reaching 143%, and the number of patients in Southeast Asia increased by 74%. China ranks first in the number of diabetic patients, with a total number of about 116.4 million people, the second is India, with about 77 million diabetic patients, and the third is the United States, with 31 million diabetic patients. In addition, China is also the country with the largest number of elderly people with diabetes. At present, the number of diabetes patients over 65 in China has reached 35.5 million, which is expected to increase to 54.3 million by 2030, and it may increase to 78.1 million by 2045. Long-term high blood sugar causes chronic damage and dysfunction of various tissues, especially eyes, kidneys, heart, blood vessels, and nerves.
The causes of diabetes mainly include genetic factors and environmental factors:
1. Genetic factors: Both type 1 and type 2 diabetes have obvious genetic heterogeneity. Diabetes has a family history, and 1/4 to 1/2 patients have a family history of diabetes. There are at least 60 genetic syndromes that can be accompanied by diabetes in the clinic. There are multiple DNA sites involved in the pathogenesis of type 1 diabetes. Among them, the DQ site polymorphism in the HLA antigen gene is most closely related. A variety of specific gene mutations have been found in type 2 diabetes, such as insulin gene, insulin receptor gene, glucokinase gene, mitochondrial gene, etc.;
2. Environmental factors: Obesity caused by excessive eating and reduced physical activity is the most important environmental factor for type 2 diabetes, which makes individuals with genetic susceptibility to type 2 diabetes prone to disease. Patients with type 1 diabetes have an abnormal immune system. Some viruses such as Coxsackie virus, rubella virus, mumps virus, etc. cause an autoimmune response and destroy insulin β cells.
Since the blood sugar content in the capillaries is not equal to the blood sugar content in the venous blood, the home blood glucose meter actually adopts a self-correction method to reduce the error.
Dynamic blood glucose monitoring (CGM) is to detect the glucose concentration of the collected interstitial fluid by implanting a subcutaneous glucose detector. In just 3 days, more than 800 blood sugar values can be recorded to form a blood sugar profile, and high blood sugar and low blood sugar that are difficult to detect by finger blood and HbA1c can be found, and blood sugar changes can be found.
However, there are still two factors restricting its market space: First, the implant can cause allergic reactions in the body. Even if the implant is biocompatible, its surface will form a layer of protein in a short time. Layer, causing the instability of the measurement results, the patient needs to replace the implant regularly, causing a certain economic burden; the second is that the implant may deviate from the original position during the limb movement, causing inaccurate measurement results.
Development status of non-invasive blood glucose monitoring technology
Because non-invasive blood glucose testing cannot measure blood glucose through direct chemical reaction with blood, it is calculated through indirect methods.
The main difficulties in realizing non-invasive blood glucose testing are as follows:
1. Blood sugar has no color in the visible light band and it is not easy to distinguish;
2. The distribution of sugar in the body is not concentrated in the blood vessels, and the glucose content in each tissue is different. In addition, the blood sugar concentration will change with the state of the body;
3. The concentration of glucose in the blood is very low, and the blood sugar content can be reduced to half of the normal value;
4. The chemical structure of blood sugar is similar to that of many other compounds in the body. Certain compounds will also bind to blood sugar in the blood, such as albumin, which interferes with the detection value.
Technical route 1: Near infrared spectroscopy technology
Technical Difficulties:
1. The intensity of the spectral signal related to blood sugar received by the sensor is weak;
2. There are many other interference factors in the tissue, which will produce near-infrared spectra similar to glucose, and many variable parameters need to be added for calibration;
3. The glucose concentration in capillaries, interstitial spaces, and veins in the human body is unevenly distributed.
Technical Route 2: Raman Spectroscopy
Technical principle: The tissue is irradiated with visible light and near-infrared light to obtain a scattering spectrum with a frequency different from the incident light, and analyze to obtain information on molecular vibration and rotation. At present, a team at MIT has shown in experiments that the spectrum has a good correlation with blood sugar.
Technical Route 3: Percutaneous Dialysis Technology
Technical principle: By applying a weak current to the skin, glucose is extracted from under the skin for detection. The back of the blood glucose meter is in contact with human skin through a layer of gel pad. There are two electrodes in the gel. When in use, the circuit is turned on and a micro current is generated through the human skin. The charged ions in the skin move to the positive and negative electrodes respectively under the action of electric current, and the glucose molecules in the tissue fluid will be “wrapped” by the charged ions and move together and enter the gel. The watch-type blood glucose meter can calculate the current blood glucose level by measuring the degree of reaction between glucose molecules and an enzyme (glucose oxidase) in the gel, and the measurement results are displayed on the “watch” screen. technical challenge:
1. The intensity of the current extracted from blood sugar is sufficient to cause damage to the skin;
2. The accuracy of equipment detection is not high;
3. It is very difficult to extract blood sugar from the skin, because the human body itself inhibits the permeation of energy substances such as glucose that play a major role in human metabolism from the skin. Therefore, when the glucose itself is extracted, the body will produce related chain reactions, which will cause The measured glucose content is no longer accurate.
Technical Route 4: Metabolic Heat Integration Method
Bobang Fangzhou, the only non-invasive blood glucose monitor that has been approved and listed by NMPA. The principle is to calculate blood glucose by testing physiological parameters related to human metabolism and basic physiological information of the human body. The testable parameters include environmental temperature, environmental humidity, and human body. Surface temperature, human body surface humidity, blood flow rate, blood oxygen saturation. Based on the basic principle of metabolic heat integration, using multi-sensor integration technology to achieve non-invasive and rapid blood glucose measurement (less than 1 minute). According to clinical trials, the consistency of the test results compared with the venous blood test results is 94.5% (that is, the proportion of Parkes consensus error table A and B); compared with the fingertip blood test results, the consistency can reach 94.4 %.
Technical route five: near infrared spectroscopy technology + metabolic heat integration method
Technical Route 6: Near Infrared Spectroscopy Technology + Percutaneous Dialysis Technology
Technical Route Seven: Other Spectroscopic Technologies
1. Terahertz Spectroscopy (Terahertz Spectroscopy)
Its wavelength is slightly higher than that of mid-infrared, and light of this wavelength has better spectral specificity for higher content substances.
2. Scattered light spectrum
Using the scattering properties of light in tissues to measure blood sugar
Case: Orsense tried to temporarily block blood circulation at the fingertips and measure blood glucose by scatter spectroscopy during the observation period. However, its main research and development head seemed to have changed the direction of research and development in 2014.
Technical route eight: other metabolites
Exhaled breath, sound: The blood glucose is measured by the content of acetone in the breath. This technology has the same problem as the urine blood glucose measurement, that is, it cannot detect hypoglycemia.
Although there are still certain technical bottlenecks and application scenarios limitations in the development of non-invasive blood glucose monitoring medical devices, in view of its remarkable convenience and economy, the future growth space is worth looking forward to.
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