Method and apparatus for noninvasively determining hematocrit
First Claim
1. An apparatus for noninvasive determination of the relative volume percent of erythrocytes, also termed the hematocrit, of whole blood having an impedance, comprising:
- means for producing a constant current at first low and second high carrier wave frequencies, said first low frequency being below a frequency zone within which said erythrocytes significantly affect the magnitude of the impedance of said whole blood, and said second high frequency being within said frequency zone;
means for stimulating a patient body portion including a pulsatile vascular compartment containing said whole blood with said first low and second high frequency current;
means for sensing voltage at each of said first low and second high carrier wave frequencies across said stimulated patient body portion;
means for detecting a signal envelope of each of said sensed voltages, each of said detected signal envelopes having a pulsatile component and a baseline component;
means for isolating the pulsatile component of each of said detected signal envelopes;
processing means for extracting at least one set of time-matched segments of said isolated pulsatile signal envelope components, creating a ratio from said isolated time-matched pulsatile signal envelope component segments of said at least one set, and for correlating said ratio to said hematocrit.
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Abstract
A method and apparatus for noninvasively determining hematocrit utilizing the frequency dependent electrical impedance characteristics of whole blood by electrically stimulating a patient body portion containing a pulsatile vascular compartment with a constant current source at two selected frequencies, one of which is high enough that the capacitive nature of erythrocytes will significantly affect the magnitude of the impedance of the blood. Sensed voltage across the stimulated body portion at the two frequencies is representative of the corresponding magnitudes, and the method further includes detecting the signal envelopes of the sensed voltages, isolating and converting the pulsatile components of the signal envelopes to the digital domain, normalizing each isolated converted pulsatile component against the voltage baseline of its carrier waveform and creating a ratio of the normalized isolated pulsatile components representative of the patient'"'"'s hematocrit. The ratio is indexed to a look-up table constructed from clinical studies correlating such ratios at the two selected frequencies to hematocrit, and the hematocrit corresponding to the created ratio is displayed. A plurality of ratios of sets of time-matched pulsatile component segments are created and averaged using a weighted averaging technique which more heavily weights ratios created from more significant segment sets, the weighted ratio average being correlated to hematocrit via the look-up table.
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Citations
30 Claims
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1. An apparatus for noninvasive determination of the relative volume percent of erythrocytes, also termed the hematocrit, of whole blood having an impedance, comprising:
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means for producing a constant current at first low and second high carrier wave frequencies, said first low frequency being below a frequency zone within which said erythrocytes significantly affect the magnitude of the impedance of said whole blood, and said second high frequency being within said frequency zone; means for stimulating a patient body portion including a pulsatile vascular compartment containing said whole blood with said first low and second high frequency current; means for sensing voltage at each of said first low and second high carrier wave frequencies across said stimulated patient body portion; means for detecting a signal envelope of each of said sensed voltages, each of said detected signal envelopes having a pulsatile component and a baseline component; means for isolating the pulsatile component of each of said detected signal envelopes; processing means for extracting at least one set of time-matched segments of said isolated pulsatile signal envelope components, creating a ratio from said isolated time-matched pulsatile signal envelope component segments of said at least one set, and for correlating said ratio to said hematocrit. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15)
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16. A method of noninvasively determining the relative volume percent of erythrocytes, also termed the hematocrit, of whole blood having an impedance, comprising:
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producing a constant current at first low and second high carrier wave frequencies, said first low frequency being below a frequency zone within which said erythrocytes significantly affect the magnitude of the impedance of said whole blood, and said second high frequency being within said frequency zone; stimulating a patient body portion including a pulsatile vascular compartment containing said whole blood with said first low and second high frequency current; sensing voltage at each of said first low and second high carrier wave frequencies across said stimulated patient body portion; detecting a signal envelope of each of said sensed voltages, each of said detected signal envelopes having a pulsatile component and a baseline component; isolating the pulsatile component of each of said detected signal envelopes; and extracting at least one set of time-matched segments of said isolated pulsatile signal envelope components, creating a ratio from said isolated time-matched pulsatile signal envelope component segments of said at least one set, and correlating said ratio to said hematocrit. - View Dependent Claims (17, 18, 19, 20, 21, 22, 23, 24, 25)
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26. An apparatus for determination of the relative volume percent of erythrocytes, also termed the hematocrit, of whole blood having an impedance, comprising:
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means for producing a constant current at first low and second high carrier wave frequencies, said first low frequency being below a frequency zone within which said erythrocytes significantly affect the magnitude of the impedance of said whole blood, and said second high frequency being within said frequency zone; means for applying said first low and second high frequency current to a volume of whole blood; means for sensing voltage at each of said first and second carrier wave frequencies across said volume; and processing means for creating a ratio from said sensed voltages, and for correlating said ratio to said hematocrit. - View Dependent Claims (27, 28, 29, 30)
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Specification