Surgery – Diagnostic testing – Measuring or detecting nonradioactive constituent of body...
Reexamination Certificate
2000-08-31
2003-07-01
Winakur, Eric F. (Department: 3736)
Surgery
Diagnostic testing
Measuring or detecting nonradioactive constituent of body...
C600S322000, C600S316000
Reexamination Certificate
active
06587704
ABSTRACT:
FIELD OF THE INVENTION
This invention is in the field of non-invasive optical measuring techniques, and relates to a method for determining parameters of the patient's blood.
BACKGROUND OF THE INVENTION
Optical methods for determining blood parameters include spectrophotometric measurements, which enable the indication of the presence of various blood constituents, based on the knowledge of their spectral behavior. These methods being applied in real medicine rather than in analytical chemistry create the basis for non-invasive (in vivo) blood tests, which present, no doubt, one of today's most exciting challenges. To make blood tests low-cost, safe and painless means to make them non-invasive.
The two main challenges, that any non-invasive optical method has to deal with, are as follows: (1) the low signal-to-noise ratio, and, (2) the large variability of individual parameters influencing the signal of concrete patients.
The main field in which the red-infrared (NIR) spectroscopy became the most widely recognized tool is the non-invasive monitoring of blood oxygenation. A pulse oximeter is the generally accepted standard of everyday clinical practice. It utilizes the so-called “AC measurement technique” which focuses on measuring only the “blood signal” of a blood perfused tissue illuminated by a predetermined range of wavelengths.
The operation of a pulse oximeter generally consists of the following: Light passing through the patient's finger comes out modulated by the waveform of his heartbeats. The amplitudes of this modulation for different light wavelengths contain information on the oxygen content in blood. Hence, a pulsatile component of the optical signal obtained from blood perfused tissue is utilized for determining the arterial blood oxygen saturation. In other words, the difference in light absorption of the tissue measured during the systole and the diastole phases 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.
Hence, for the AC signal, arterial blood plays the role of the key absorber. The spectral behaviors of Hb and HbO
2
absorbtion differ strongly, so the oxygen saturation can be extracted from the results of the measurements. To summarize the implementation of pulse oximetry signals as carried out today, it presents oximetry as an absorption-related method based on the convolution of natural kinetics (AC/DC ratio is analysed) and spectrophotometric behavior of various ingredients. The generic limitations of this method are as follows: First, it has a rather low specificity, since only absorption variations are considered, and the scattering is treated as an inevitable obstacle (John M. Steinke, A. P. Sheperd, “Role of Light Scattering in Spectrophotometric Measurements of Arteriovenous Oxygen Difference”, IEEE Trans. BME-33, Aug. 8, 1986, p.729-734). Second, it has a rather low signal-to-noise ratio resulting from the low magnitude of the AC signal taken from natural blood kinetics.
When the first limitation has never been touched in practical devices (the scattering is considered to be too delicate and variable to deal with anywhere but in fundamental research), various methods have been suggested to improve the signal-to-noise ratio. Nearly all of them deal with artificially induced volumetric changes of either arterial or venous blood flow.
U.S. Pat. No. 4,883,055 discloses a method and device for artificially inducing blood pulse for use with a pulse oximeter. A cuff wrapped around a body member having an artery upstream from a testing site is adapted for applying a squeezing pulse to the body member, the squeezing pulse being synchronized with a normal blood pulse. Oxygen saturation in the arterial blood is determined based on spectrophotometric non-invasive measurements, which are effected according to the general approach of the above-mentioned AC-measurement technique.
U.S. Pat. No. 4,927,264 discloses a non-invasive apparatus and method for measuring blood constituents in venous blood. This technique utilizes the obstruction of a patient's venous blood stream, while the arterial blood stream is not obstructed. The venous blood stream is made time-variant by applying pressure with a peak value of the minimum blood pressure to a proximal portion from a measuring part.
U.S. Pat. No. 5,638,816 discloses a blood glucose monitoring system, which provides for inducing an active pulse in the blood volume of a patient according to a predictable cyclic pattern. The induction of an active pulse causes a cyclic change in the flow of arterial blood through a fleshy medium undergoing the test. By actively inducing a change of the blood volume, modulation of the volume of blood can be obtained to provide a greater signal-to-noise ratio. This enables constituents in blood to be detected at concentration levels below those previously detectable in a non-invasive system. Radiation, which passes through the fleshy medium, is sensed by a detector which generates a signal indicative of the intensity of the detected radiation. Signal processing is performed on the electrical signal to separate those optical characteristics of the electrical signal, which are associated with the optical characteristics of the blood.
To summarize, the absolute majority of existing devices in the field of non-invasive blood measurements utilizes the natural kinetics with all its limitations in signal-to-noise ratio.
SUMMARY OF THE INVENTION
The two main limitations of the most popular non-invasive methods are connected with the interpretation based on the omission of the scattering effects that results in the low specificity of measurements, and with the utilization of natural kinetics resulting in low signal-to-noise ratio. As a result, these methods are limited by the measurement of ingredients that have highly specific spectral behavior and are present in high concentrations (as HbO
2
does).
There is accordingly a need in the art to facilitate non-invasive optical measurements of various blood parameters, by providing a novel method enabling, on the one hand, the measurements with high signal-to-noise ratio, and, on the other hand, the determination of various blood parameters, also other than the oxygen saturation. These parameters may include the concentration of a substance in blood, such as glucose, hemoglobin, drugs or cholesterol, or other important blood parameters such as ESR, etc.
For blood parameters other than oxygen saturation, the determination is too problematic, because their absorption spectral behavior in red and near infrared regions is not as remarkable as for the oxygenized hemoglobin. Hence, the main limitations on the way of expanding the non-invasive techniques to the measurements different from pulse oximetry are associated with the limited selectivity of the absorption based method. In case of realistic accuracy of medical measurements for the absorption, which is not peculiar enough, the individuality of the patient becomes the main governing factor. To get rid of this limitation, scattering variations, which are more specific and sensitive than the absorption ones, have to be taken into account.
It is thus a major feature of the present invention to provide such a technique that takes into consideration both the light scattering and the light absorption in order to take into account the individual variability properly (contrary to the ideology of calibration of pulse oximeters, where light scattering is mostly ignored).
The basic idea of the invention is to combine the advantages of a high signal-to-noise ratio provided by a condition of artificial kinetics of optical characteristics (rather than natural kinetics of pulse oximetry) with high selectivity of light scattering based characteristics. The technique of the present invention is based on the convolution of spectral characteristics and artificial kinetics, and utilizes a particular kind of artificial kinetics favoring the high changes
Fine Ilya
Shvartsman Leonid
Fitch Even Tabin & Flannery
Kremer Matthew
Orsense Ltd.
Winakur Eric F.
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