Surgery – Diagnostic testing – Measuring or detecting nonradioactive constituent of body...
Reexamination Certificate
1999-12-01
2001-10-16
Winakur, Eric F. (Department: 3736)
Surgery
Diagnostic testing
Measuring or detecting nonradioactive constituent of body...
C356S039000
Reexamination Certificate
active
06304767
ABSTRACT:
BACKGROUND
This invention relates to measurement of blood hematocrit (Hct).
Hematocrit is the volume percent of red blood cells in a blood sample and is one of the most commonly performed blood tests. The standard method for measuring hematocrit involves collecting a blood sample in a capillary tube and centrifuging the tube to separate out the red blood cells from the plasma. By measuring the height of a resulting layer of red blood cells in the capillary and referencing it to the total blood volume, the volume percent of red blood cells can be quantified. Hematocrit measurements on blood samples are now often made with more automated techniques such as conductivity measurements.
Hematocrit can also be measured non-invasively. Two approaches have been reported for such non-invasive monitoring of hematocrit, an optical approach and an impedance method. Impedance methods are found to be inaccurate when protein and electrolyte levels are abnormal, such as when blood is replaced with crystalloid solutions, as would happen during resuscitation of trauma victims. All of the reported optical techniques are variations on oximetric methods where hematocrit is measured using only the concentrations of oxygenated and deoxygenated hemoglobin. The concentrations of oxygenated and deoxygenated hemoglobin are directly measured by absorption or reflection using 2 to 4 wavelengths of light in the near-infrared region of the hemoglobin spectrum.
SUMMARY
The invention provides a non-invasive optical and mathematical method to measure hematocrit with an accuracy of approximately 99%. The accuracy results from the complete analysis provided by the new optical method, which measures blood hematocrit by quantifying a plurality of red blood cell constituents.
In general, in one aspect, the invention features a method for determining blood hematocrit. The method includes irradiating blood with optical radiation having a selected range of optical wavelengths to produce an optical spectrum. The wavelengths in the selected range are affected by a plurality of red blood cell constituents. Hematocrit is determined by processing the optical spectrum with a mathematical model. The model is constructed by relating optical properties of the plurality of red blood cell constituents to known blood hematocrit.
Embodiments of this aspect of the invention may include one or more of the following features. The plurality of red blood cell constituents include all hemoglobins and cellular bodies, e.g., cellular nuclei and cellular membranes. The mathematical model is determined prior to irradiating the blood by processing optical spectra having known hematocrit values with a mathematical algorithm, such as a partial least-squares (PLS) fitting algorithm. Alternatively, this model can feature a non-linear mathematical equation relating hematocrit to a reflection or absorption spectrum taken from a plurality of red blood cell constituents. In particular, the optical spectra used to construct the model can be recorded on an extracted blood sample.
The optical radiation can be between 400 and 2000 nm. In particular, the radiation can be between 500 and 1100 nm. The optical spectrum can be produced by irradiating the blood in vivo or in vitro and then collecting radiation that is either reflected or scattered from a plurality of red blood cell constituents or transmitted through a plurality of red blood cell constituents.
In the processing step, the optical spectrum is compared with the mathematical model to determine the blood hematocrit.
According to another aspect of the invention, the invention features a device for determining blood hematocrit. The device includes an array of light sources for delivering radiation to the sample, each of which can deliver radiation at a unique range of optical wavelengths. The device also includes a power supply and a modulation system in electrical contact with each of the light sources. The modulation system is configured to modulate electrical power delivered from the power supply to each of the light sources. A detection system included in the device features a first optical detector and a plurality of second optical detectors. The first optical detector is configured to receive radiation from the sample. The plurality of second optical detectors is configured to receive radiation from each of the light sources.
After receiving the radiation, the first optical detector generates a first set of radiation-induced electrical signals, each corresponding to radiation emitted from a separate light source to the sample. The plurality of second optical detectors generates a second set of radiation-induced electrical signals, each corresponding to radiation emitted from a separate light source. A signal processor receives the first and second sets of electrical signals and, in response, generates first and second sets of digital, electrical signals. These signals are then received by a microprocessor. The microprocessor is programmed to process the signals to determine a first spectrum. The first spectrum (or a spectrum determined from the first spectrum) is then compared to a mathematical model to determine blood hematocrit. The detection system can further include phase-sensitive detection electronics in electrical contact with the first optical detector and the plurality of second optical detectors to detect radiation generated at the unique frequency. For example, the phase-sensitive detection electronics are incorporated in a lock-in amplifier.
Embodiments of this aspect of the invention can include one or more of the following features. The microprocessor can be programmed to calculate the mathematical model prior to processing the first set of digital, electrical signals. In addition, the radiation detected by the plurality of second detectors can be processed and used to determine a reference spectrum which, in turn, is used to calculate the reflection spectrum. Inclusion of the reference spectrum allows variations in the intensities of each light source to be taken into account. The signal processor and microprocessor can also perform signal averaging of the electric signals. In addition, the microprocessor is programmed to calculate the mathematical model before processing the first set of digital signals.
The plurality of second optical detectors can be equal to two. In particular, the plurality of second optical detectors can be equal to the number of light sources. For example, the device includes seven light sources. Each light source can be a light-emitting diode (LED) or a laser diode. The optical wavelengths emitted by the light sources are collimated by a molded lens array. In one embodiment, the optical wavelengths can be visible and near-infrared wavelengths. For example, the wavelengths can be 400 and 2000 nm, e.g., between 500 and 1100 nm. In particular, each light source delivers infrared radiation having a bandwidth of between about 0.1 and 100 nm. In addition, the light sources are adapted to deliver optical wavelength selected to be affected by the absorption and scattering from a plurality of red blood cell constituents.
In another aspect, the invention features a fiber optic device for determining blood hematocrit including an array of light sources for delivering radiation to the sample. The light sources are attached to a mount and a fiber optic cable is attached to each light source. The fiber optic cable includes a delivery fiber for delivering radiation to the sample, a reference fiber for delivering radiation to a detection system, a beam splitter for splitting light into the delivery fiber and the reference fiber, and a signal fiber for delivering radiation reflected by the sample to a detection system.
The detection system includes a first optical detector attached to the mount and coupled to the signal fiber for receiving radiation from the sample. The detection system also includes a second optical detector which is also attached to the mount and coupled to each reference fiber for receiving radiation directly from each of the light sources. The detec
Micheels Ronald H.
Soller Babs R.
Fish & Richardson P.C.
Polestar Technologies, Inc.
Winakur Eric F.
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