System and method for in-vivo hematocrit measurement using impedance and pressure plethysmography
First Claim
1. A method of measuring the hematocrit of blood perfusing a living body part, the method comprising:
- driving first and second alternating currents of different frequencies between separate points on the body part;
monitoring first and second signals induced in the body part by the respective first and second currents;
generating first and second pulsatile signals and first and second baseline signals from the respective first and second induced signals; and
determining the hematocrit of the blood from the first and second pulsatile signals and the first and second baseline signals.
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Abstract
The hematocrit of blood (i.e., the percentage of whole blood volume occupied by red blood cells) perfusing a finger is determined by stimulating the finger with two current frequencies, one relatively high (e.g., 10 MHZ) and the other relatively low (e.g., 100 KHz). Voltages induced in the finger in response to the two current frequencies are then captured and separated into baseline and pulsatile components. The hematocrit is determined as a function of the ratio of the high frequency pulsatile component to the low frequency pulsatile component, multiplied by the ratio of the square of the low frequency baseline component to the square of the high frequency baseline component. The signal-to-noise ratio of the captured voltages can be enhanced by the application of external pressure to the finger, such as by applying a pressure cuff to the finger.
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Citations
30 Claims
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1. A method of measuring the hematocrit of blood perfusing a living body part, the method comprising:
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driving first and second alternating currents of different frequencies between separate points on the body part; monitoring first and second signals induced in the body part by the respective first and second currents; generating first and second pulsatile signals and first and second baseline signals from the respective first and second induced signals; and determining the hematocrit of the blood from the first and second pulsatile signals and the first and second baseline signals. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15)
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16. A system for measuring the hematocrit of blood perfusing a living body part, the system comprising:
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circuitry for driving first and second alternating currents of different frequencies between separate points on the body part; circuitry for monitoring first and second signals induced in the body part by the respective first and second currents; circuitry coupled to the monitoring circuitry for generating first and second pulsatile signals and first and second baseline signals from the respective first and second induced signals; and circuitry coupled to the generating circuitry for determining the hematocrit of the blood from the first and second pulsatile signals and the first and second baseline signals. - View Dependent Claims (17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30)
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Specification