Surgery – Diagnostic testing – Measuring or detecting nonradioactive constituent of body...
Reexamination Certificate
2002-11-05
2004-03-23
Hindenburg, Max F. (Department: 3736)
Surgery
Diagnostic testing
Measuring or detecting nonradioactive constituent of body...
C600S335000
Reexamination Certificate
active
06711424
ABSTRACT:
FIELD OF THE INVENTION
This invention is in the field of optical measuring techniques and relates to a method for determining desired parameters of the patient's blood, for example, the concentration of a substance in blood, such as glucose, hemoglobin, drugs or cholesterol, or other important blood parameters such as oxygen saturation. The invention is particularly useful for non-invasive measurements.
BACKGROUND OF THE INVENTION
Optical methods of determining the chemical composition of blood are typically based on spectrophotometric measurements enabling the indication of the presence of various blood constituents based on known spectral behaviors of these constituents. These spectrophotometric measurements may be effected either in vitro or in vivo. The measurements in vitro are invasive, i.e. require a blood sample to be physically withdrawn and examined. At present, these measurements have become unpopular, due to the increasing danger of infection.
The non-invasive optical measurements in vivo may be briefly divided into two main groups based on different methodological concepts. The first group represents a so-called “DC measurement technique”, and the second group is called “AC measurement technique”.
According to the DC measurement technique, any desired location of a blood perfused tissue is illuminated by the light of a predetermined spectral range, and the tissue reflection and/or transmission effect is studied. Although this technique provides a relatively high signal-to-noise ratio, as compared to the AC measurement technique, the results of such measurements depend on all the spectrally active components of the tissue (i.e. skin, blood, muscles, fat, etc.), and therefore need to be further processed to separate the “blood signals” from the detected signals. Moreover, proportions of the known components vary from person to person and from time to time. To resolve this problem, calibration must periodically be provided, which constitutes an invasive blood test and therefore renders the DC technique of optical measurements to be actually invasive.
The AC measurement technique focuses on measuring only the “blood signal” of a blood perfused tissue illuminated by a predetermined range of wavelengths. To this end, what is actually measured is a time-dependent component only of the total light reflection or light transmission signal obtained from the tissue. A typical example of the AC measurement technique is the known method of pulse oximetry, wherein a pulsatile component of the optical signal obtained from a blood perfused tissue is utilized for determining arterial blood oxygen saturation. In other words, the difference in light absorption of the tissue measured during the systole and the diastole is considered to be caused by blood that is pumped into the tissue during the systole phase from arterial vessels, and therefore has the same oxygen saturation as in the central arterial vessels.
The major drawback of the AC measurement technique is its relatively low signal-to-noise ratio, especially in cases where an individual has a poor cardiac output, insufficient for providing a pulsatile signal suitable for accurate measurements.
Various methods have been suggested to enhance the natural pulsatile signal of an individual for effecting non-invasive optical measurements, and are disclosed for example in the following patents: U.S. Pat. No. 4,883,055; U.S. Pat. No. 4,927,264; and U.S. Pat. No. 5,638,816. All these techniques utilize the artificially induced volumetric changes of either arterial or venous blood. Since each of these techniques is specific about the kind of blood under test, they all impose severe restrictions on the value of the artificially applied pressure. This is due to different “disturbing pressure values” allowed for different kinds of blood flow. It means that for each kind of blood flow, there is a pressure value that disturbs specifically this kind of flow much more than any other kind. For example, when the artificial pressure at a value of 60 mmHg is applied to a proximal body part, the venous blood flow will be affected, whereas the arterial blood flow will not be affected, since the individual's diastolic pressure is usually higher than 60 mmHg. The applied artificial pressure definitely should not exceed pressures causing substantial deformation of the tissue, since only blood flow changes are supposed to be detected by optical measurements, and the measurements are to be effected in synchronism with the artificial pulse. However, if such an artificially induced pulse causes uncontrollable changes of the optical properties of the tissue, these changes cannot be distinguished from those caused by the blood flow fluctuations which are the target of the measurements.
SUMMARY OF THE INVENTION
There is a need in the art to facilitate the determination of various parameters of the patient's blood, by providing a novel method of optical measurements which can be utilized in a non-invasive manner for in vivo determination of such parameters as the concentration of a substance in blood (e.g., hemoglobin, glucose), oxygen saturation, the difference between the refraction indexes of hemoglobin and plasma in the patient's blood, and/or Erythrocyte Aggregation Rate (EAR).
It is a major feature of the present invention to provide such a method that is universal and does not depend on such conditions as concrete kinetics, aggregation shape, etc. which vary from patient to patient.
The present invention takes advantage of the technique disclosed in the co-pending application assigned to the assignee of the present application. The main idea underlying this technique is based on the fact that the light response characteristics (i.e., absorption and/or scattering) of a blood perfused medium dramatically changes when a character of blood flow changes. It has been found by the inventors, that the optical characteristics of a blood perfused fleshy medium (e.g., the patient's finger) start to change in time, when causing blood flow cessation. In other words, once the blood flow cessation state is established, the optical characteristics start to change dramatically, such that they differ from those of the fleshy medium with a normal blood flow by about 25 to 45%, and sometimes even by 60%. Hence, the accuracy (i.e., signal-to-noise ratio) of the optical measurements can be substantially improved by performing at least two timely separated measurement sessions, each including at least two measurements with different wavelengths of incident radiation.
The main idea of the present invention is based on the investigation that the changes of the light response of a blood perfused fleshy medium at the state of the blood flow cessation (either monotonous or not, depending on the wavelength of incident radiation) are caused by the changes of the shape and average size of the scattering centers in the medium, i.e., red blood cells (RBC) aggregation (Rouleaux effect). The main principles of this effect are disclosed, for example, in the article “Quantitative Evaluation of the Rate of Rouleaux Formation of Erythrocytes by Measuring Light Reflection (“Syllectometry”)”, R. Brinkman et al., 1963.
At the state of the blood flow cessation, when there is actually no blood flow, no shear forces prevent the erythrocytes' aggregation process. Hence, the light response (transmission) of the blood perfused fleshy medium undergoing the occlusion, which causes the blood flow cessation, can be considered as the time dependence of scattering in a system with growing scatterers.
Generally, light response of a medium is defined by the scattering and absorption properties of the medium. According to the model of the present invention, at the state of blood flow cessation under proper conditions, the crucial parameter defining the time evolution of the light response is a number of erythrocytes in aggregates. Therefore, it can be concluded that the average size of aggregates also changes with time. The scattering properties of blood depend on the size and s
Fine Ilya
Shvartsman Leonid
Browdy and Neimark , P.L.L.C.
Hindenburg Max F.
Kremer Matthew
Orsense Ltd.
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