Continuous, non-invasive technique for measuring blood pressure using impedance plethysmography
First Claim
1. An apparatus for continuously and non-invasively monitoring blood pressure in an animal, said apparatus comprising:
- a device which measures impedance of the animal and from that impedance detects when a blood volume pulse is emitted from the heart of the animal;
a sensor which detects a blood volume pulse occurring at another location in the animal;
a timer connected to the device and to the sensor, wherein the timer measures an interval of time which elapses between when a blood volume pulse is emitted from the heart and a blood volume pulse occurring at the other location in the animal; and
a processor which derives the blood pressure of the animal from the interval of time measured by the timer.
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Accused Products
Abstract
Blood pressure is measured using the pulse transit time required for the blood volume pulse to propagate between two locations in an animal. Impedance plethysmography is employed to detect when the blood volume pulse occurs at one location. The plethysmograph may detect thoracic impedance to determine when the aortic heart valve opens or it may detect impedance at one location on a limb of the animal. Occurrence of the blood volume pulse at another location can be determined by impedance plethysmography or another technique, such as pulse oximetry. The calculation of cardiac stroke volume can be employed to compensate the derivation of the blood pressure for effects due to blood vessel compliance. A nonblood pressure monitor may periodically provide a reference blood pressure measurement that is used calibrate derivation of the blood pressure based on the pulse transit time.
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Citations
25 Claims
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1. An apparatus for continuously and non-invasively monitoring blood pressure in an animal, said apparatus comprising:
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a device which measures impedance of the animal and from that impedance detects when a blood volume pulse is emitted from the heart of the animal;
a sensor which detects a blood volume pulse occurring at another location in the animal;
a timer connected to the device and to the sensor, wherein the timer measures an interval of time which elapses between when a blood volume pulse is emitted from the heart and a blood volume pulse occurring at the other location in the animal; and
a processor which derives the blood pressure of the animal from the interval of time measured by the timer. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14)
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11. The apparatus as recited in claim 9 wherein the processor derives the blood pressure (BP) from the interval of time (PTT) according to the expression:
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12. The apparatus as recited in claim 1 wherein the sensor comprises an impedance plethysmograph that measures a given impedance of the animal at the other location, and determines from that given impedance when the blood volume pulse occurs at the other location.
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13. The apparatus as recited in claim 1 further comprising a nonblood pressure monitor, which periodically supplies a reference measurement of blood pressure to the processor.
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14. The apparatus as recited in claim 13 wherein the processor employs the reference measurement of blood pressure to calibrate derivation of the blood pressure from the interval of time measured by the timer.
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15. An apparatus for non-invasively monitoring blood pressure in an animal, said apparatus comprising:
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an impedance cardiograph that measures thoracic impedance of the animal and determines from the thoracic impedance when a blood volume pulse is emitted from the heart;
electrocardiograph connected to the impedance cardiograph;
a sensor which detects when a blood volume pulse occurs at a second location in the animal;
a timer connected to the impedance cardiograph and the sensor, wherein the timer measures an interval of time which elapses between when a blood volume pulse is emitted from the heart and when a blood volume pulse occurs at the second location; and
a processor which derives tie blood pressure of the animal from the interval of time measured by the timer. - View Dependent Claims (16, 17, 18, 19, 20)
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21. A method for continuously and non-invasively monitoring blood pressure in an animal having a heart, said method comprising:
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measuring thoracic impedance the animal;
determining from the thoracic impedance when a blood volume pulse is emitted from the heart;
detecting a blood volume pulse occurring at another location in the animal;
measuring an interval of time which elapses between when a blood volume pulse is emitted from the heart and occurrence of the blood volume pulse at the other location; and
deriving the blood pressure of the animal from the interval of time measured by the timer. - View Dependent Claims (22, 23, 24, 25)
producing an electrocardiogram waveform representing activity of a heart in the animal;
deriving a cardiac stroke volume measurement in response to the thoracic impedance and the electrocardiogram waveform; and
employing the cardiac stroke volume measurement to compensate derivation of the blood pressure of the animal for effects due to blood vessel compliance.
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23. The method as recited in claim 21 wherein detecting when a blood volume pulse occurs at a second location comprises measuring an impedance at the second location of the animal.
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24. The method as recited in claim 21 further comprising periodically activating a nonblood pressure monitor to produce a reference measurement of blood pressure.
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25. The method as recited in claim 24 further comprising calibrating deriving the blood pressure of the animal using the reference measurement of blood pressure.
Specification