Surgery – Diagnostic testing – Measuring or detecting nonradioactive constituent of body...
Reexamination Certificate
2000-10-20
2003-02-25
Winakur, Eric F. (Department: 3736)
Surgery
Diagnostic testing
Measuring or detecting nonradioactive constituent of body...
Reexamination Certificate
active
06526298
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to devices and methods for the non-invasive determination of concentrations of analytes in a human subject in vivo and to methods of improving calibration of these devices and methods.
2. Discussion of the Art
Non-invasive monitoring of concentrations of analytes in the human body by means of optical devices and optical methods is an important tool for clinical diagnosis. “Non-invasive” (alternatively referred to herein as “NI”) monitoring techniques measure in vivo concentrations of analytes in the blood or in the tissue without the need for obtaining a blood sample from the human body. As used herein, a “non-invasive” technique is one that can be used without removing a sample from, or without inserting any instrumentation into, the human body. The ability to determine the concentration of an analyte, or a disease state, in a human subject without performing an invasive procedure, such as removing a sample of blood or a biopsy specimen, has several advantages. These advantages include ease in performing the test, reduced pain and discomfort to the patient, and decreased exposure to potential biohazards. These advantages tend to promote increased frequency of testing, accurate monitoring and control of a disease condition, and improved patient care. A well-known non-invasive optical technique is pulse oximetry. Oxygenation of blood in the tissue and cerebral oxygen saturation can be measured by this technique, and the measurements can be used for clinical applications. Non-invasive determination of the hemoglobin concentration and the hematocrit value have the potential to be applied for diagnosis of anemia in infants and mothers, for localizing tumors, and for diagnosis of hematoma and internal bleeding.
Non-invasive diagnosis and monitoring of diabetes may be the most important non-invasive diagnostic procedure. Diabetes mellitus is a chronic disorder of carbohydrate, fat, and protein metabolism characterized by an absolute or relative insulin deficiency, hyperglycemia, and glycosuria. At least two major variants of the disease have been identified. “Type I” accounts for about 10% of diabetics and is characterized by a severe insulin deficiency resulting from a loss of insulin-secreting beta cells in the pancreas. The remainder of diabetic patients suffer from “Type II”, which is characterized by an impaired insulin response in the peripheral tissues (Robbins, S. L. et al.,
Pathologic Basis of Disease,
3
rd
Edition, W. B. Saunders Company, Philadelphia, 1984, p. 972). If uncontrolled, diabetes can result in a variety of adverse clinical manifestations, including retinopathy, atherosclerosis, microangiopathy, nephropathy, and neuropathy. In its advanced stages, diabetes can cause blindness, coma, and ultimately death.
Tight control of blood glucose level in the “normal range”, 60-120 mg/dL, is necessary for diabetics to avoid or reduce complications resulting from hypoglycemia and hyperglycemia. To achieve this level of control, diabetics should test their blood glucose level several times per day. Thus, there is a need for accurate and frequent, preferably continuous, glucose monitoring to reduce the effects of diabetes.
U.S. Pat. Nos. 5,086,229; 5,324,979; and 5,237,178 describe non-invasive methods for measuring blood glucose level involving radiation in the near infrared region of the electromagnetic spectrum (600 nm to 1200 nm). In these methods, a blood-containing body part (e.g., a finger) is illuminated by one or more light sources, and one or more detectors detect the light transmitted through the body part. A glucose level is derived from a comparison to reference spectra for glucose and background interferants.
U.S. Pat. Nos. 5,362,966; 5,237,178; 5,533,509; and 4,655,225 describe the use of radiation in the near infrared range of the electromagnetic spectrum, that is, from 1200 nm to about 3000, for the optical measurement of blood glucose level. The principles of operation are similar to those described for measurements employing radiation in the 600 nm to 1200 nm range, except that the light penetration depth in this wavelength range is less than that in the 600 nm to 1200 nm wavelength range. As a consequence, most optical measurements in this region of the electromagnetic spectrum use an arrangement based on reflectance measurement rather than transmittance measurement. U.S. Pat. Nos. 5,313,941; 5,115,133; 5,481,113; 5,452,716; 5,515,847; 5,348,003; and DE 4242083 describe optical measurements in the infrared region of the electromagnetic spectrum employing radiation in the range of from about 3000 nm to about 25000 nm.
These glucose determination methods of the prior art are silent as to the effect of temperature at the measurement site on the optical signal. They are also silent as to the effect of temperature on the propagation of light in tissue and to the effect of modulating the temperature between preset limits during the optical measurement. U.S. Pat. Nos. 3,628,525; 4,259,963; 4,432,365; 4,890,619; 4,926,867; 5,131,391; and European Patent Application EP 0472216 describe oximetry probes having heating elements designed to be placed against a body part. U.S. Pat. No. 5,148,082 describes a method for increasing the blood flow in a patient's tissue during a photoplethysmography measurement by heating the tissue with a semiconductor device mounted in a sensor.
Spatially resolved diffuse reflectance techniques have been described U.S. Pat. Nos. 5,551,422; 5,676,143; 5,492,118; 5,057,695, European Patent Application EP 0810429. In these techniques, light is introduced into a sample and the intensity of the light re-emitted from the sample is measured at several distances from the site at which light is introduced into the sample. U.S. Pat. Nos. 5,187,672; 5,122,974; 5,492,769 and 5,492,118 describe frequency-domain reflectance measurements, which use optical systems similar to those used for spatially resolved diffuse reflectance measurements, except that the light source and the detector are modulated at a high frequency.
A major assumption for using these techniques is that tissue can be represented as an infinite-homogeneous slab. These techniques ignore the nature of skin, which is a layered structure. Further, these techniques ignore the effect of the temperature of the skin on propagation of light in cutaneous layers. U.S. Pat. No. 5,551,422 describes a glucose sensor utilizing spatially resolved diffuse reflectance techniques, wherein the sensor is brought to a specified temperature, preferably somewhat above normal body-temperature, with a thermostatically controlled heating system.
The light penetration depth in tissue depends on wavelength of the illuminating light. Generally, light in the near infrared region of the electromagnetic spectrum penetrates deeper into the tissue at longer wavelengths within the therapeutic window (600 nm to 1300 nm). Temperature affects the light penetration depth in tissue. Light at a given wavelength will penetrate deeper into a tissue, such as skin, as temperature of the tissue is lowered.
When human skin is illuminated by light of a single wavelength and the temperature of the skin is uncontrolled, the light penetration depth will vary from person to person, depending on the temperature of the subject's skin. When the skin is illuminated at a plurality of wavelengths and the temperature of the skin is not controlled, there will be even greater variation in light penetration depth. The ultimate result will be an erroneous estimate of optical parameters, and consequently, an erroneous determination of the concentration of an analyte in vivo.
U.S. application Ser. No. 09/080,470, filed May 18, 1998, assigned to the assignee of this application, and WO 99/59464 describe a non-invasive glucose sensor employing a means for controlling the temperature of a sample. One purpose of controlling the temperature of the skin during the optical measurement is to minimize the effect of physiological variables.
Although a variety of detecti
Hanna Charles F.
Kantor Stanislaw
Khalil Omar S.
Yeh Shu-jen
Abbott Laboratories
Weinstein David L.
Winakur Eric F.
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