Vital sign monitor for cufflessly measuring blood pressure using a pulse transit time corrected for vascular index
First Claim
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1. A system for monitoring a patient'"'"'s blood pressure parameter, the system comprising:
- an optical sensor configured to attach to the patient and generate a time-dependent optical waveform representing a flow of blood within the patient;
an electrode system configured to attach to the patient and generate a time-dependent electrical waveform representing activity of the patient'"'"'s heart;
a calibration system configured to attach to a portion of the patient'"'"'s body and apply a pressure; and
a processing component programmed to;
i) determine a first set of pulse transit times, wherein each transit time within the set is a measure of a separation in time of a first feature of the time-dependent electrical waveform and a second feature of the time-dependent optical waveform, the first set of pulse transit times measured while the calibration system applies the pressure to the portion of the patient'"'"'s body;
ii) analyze the first set of pulse transit times with a mathematical model that processes a pressure-induced change in transit time to determine a calibration representing properties of the patient'"'"'s blood circulatory system; and
iii) calculate the blood pressure parameter from a second pulse transit time and the calibration, the second pulse transit time measured while the calibration system does not apply pressure to the portion of the patient'"'"'s body.
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Abstract
A method and apparatus for measuring a patient'"'"'s blood pressure featuring the following steps: 1) measuring a time-dependent optical waveform with an optical sensor; 2) measuring a time-dependent electrical signal with an electrical sensor; 3) estimating the patient'"'"'s arterial properties using the optical waveform; 4) determining a pulse transit time (PTT) from the time-dependent electrical signal and the time-dependent optical waveform; and 5) calculating a blood pressure value using a mathematical model that includes the PTT and the patient'"'"'s arterial properties.
42 Citations
23 Claims
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1. A system for monitoring a patient'"'"'s blood pressure parameter, the system comprising:
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an optical sensor configured to attach to the patient and generate a time-dependent optical waveform representing a flow of blood within the patient; an electrode system configured to attach to the patient and generate a time-dependent electrical waveform representing activity of the patient'"'"'s heart; a calibration system configured to attach to a portion of the patient'"'"'s body and apply a pressure; and a processing component programmed to;
i) determine a first set of pulse transit times, wherein each transit time within the set is a measure of a separation in time of a first feature of the time-dependent electrical waveform and a second feature of the time-dependent optical waveform, the first set of pulse transit times measured while the calibration system applies the pressure to the portion of the patient'"'"'s body;
ii) analyze the first set of pulse transit times with a mathematical model that processes a pressure-induced change in transit time to determine a calibration representing properties of the patient'"'"'s blood circulatory system; and
iii) calculate the blood pressure parameter from a second pulse transit time and the calibration, the second pulse transit time measured while the calibration system does not apply pressure to the portion of the patient'"'"'s body. - View Dependent Claims (2, 3, 4, 5, 6, 7, 15, 16, 17, 18, 19, 20, 21)
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8. A method of monitoring a patient'"'"'s blood pressure parameter, the method comprising:
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detecting a time-dependent optical waveform from a flow of blood within the patient; detecting a time-dependent electrical waveform representing activity of the patient'"'"'s heart; applying a pressure to a portion of the patient'"'"'s body while detecting the optical waveform and the electrical waveform; analyzing the time-dependent optical waveform and the time-dependent electrical waveform while pressure is applied to a portion of the patient'"'"'s body to determine a set of pulse transit times featuring values that change with the amount of applied pressure, wherein each pulse transit time within the set is a measure of a separation in time of a first feature of the time-dependent electrical waveform and a second feature of the time-dependent optical waveform, the set of pulse transit times representing properties of the patient'"'"'s blood circulatory system; processing the pressure-dependent change in pulse transit times within the set of pulse transit times with a mathematical model to determine a calibration; measuring a second pulse transit time for the patient while pressure is not applied to the portion of the patient'"'"'s body; and determining the blood pressure parameter from the second pulse transit time and the calibration. - View Dependent Claims (9, 10, 11, 12)
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13. A system for monitoring a patient'"'"'s blood pressure parameter, the system comprising:
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an optical sensor configured to attach to the patient and generate a time-dependent optical waveform representing a flow of blood within the patient; an electrode system configured to attach to the patient and generate a time-dependent electrical waveform representing activity of the patient'"'"'s heart; a calibration system configured to attach to a portion of the patient and apply a pressure; and a processing component programmed to;
i) determine a set of pulse transit times while the calibration system applies pressure to the portion of the patient, with each pulse transit time within the set representing a measure of a separation in time of a first feature of the time-dependent electrical waveform and a second feature of the time-dependent optical waveform;
ii) analyze the pressure-dependent change in values of pulse transit times within the set of pulse transit times with a mathematical model to determine a vascular index representing properties of the patient'"'"'s blood circulatory system; and
iii) use the vascular index and a pulse transit time measured when pressure is not applied by the calibration system to determine a value of a blood pressure parameter for the patient.
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14. A method of monitoring a patient'"'"'s blood pressure parameter, the method comprising:
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generating a time-dependent optical waveform from a flow of blood within the patient; detecting a time-dependent electrical waveform representing activity of the patient'"'"'s heart; applying a pressure to a portion of the patient'"'"'s body; analyzing the time-dependent optical waveform and the time-dependent electrical waveform while pressure is applied to a portion of the patient'"'"'s body to determine a set of pulse transit times, with each transit time representing a measure of a separation in time of a first feature of the electrical waveform and a second feature of the optical waveform, and a pressure-dependent change in the values of transit times indicating a vascular index representing properties of the patient'"'"'s blood circulatory system; processing the pressure-dependent change in the values of transit times within the set of pulse transit times with a mathematical model to determine a calibration; determining a pulse transit time for the patient when pressure is not applied to a portion of the patient'"'"'s body; and using the calibration and a measured pulse transit time for the patient to determine a value of the blood pressure parameter for the patient.
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22. A system for monitoring a patient'"'"'s blood pressure parameter, comprising body-worn sensors for measuring optical and electrical waveforms, a pressure-applying calibration system, a first processing system for determining a transit time from the optical and electrical waveforms, a second processing system for calculating a calibration from a pressure-induced change in transit time caused by the calibration system, and a third processing system for calculating the blood pressure parameters from the calibration and a transit time.
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23. A system for monitoring a patient'"'"'s blood pressure parameter, the system comprising:
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an optical sensor configured to attach to the patient and generate a time-dependent optical waveform representing a flow of blood within the patient; an electrode system configured to attach to the patient and generate a time-dependent electrical waveform representing activity of the patient'"'"'s heart; and a processing component programmed to;
i) determine a first pulse transit time, which is a measure of a separation in time of a first feature of the time-dependent electrical waveform and a second feature of the time-dependent optical waveform;
ii) analyze the optical waveform to determine its second mathematical derivative;
iii) determine a set of fiducial points from the second mathematical derivative;
iv) process the set of fiducial points with a mathematical model to estimate a vascular index representing properties of the patient'"'"'s blood circulatory system; and
v) determine an estimate of the blood pressure parameter from a measured second pulse transit time for the patient and the vascular index measured from the optical waveform used to calculate the second pulse transit time.
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Specification