Vital sign monitor for cufflessly measuring blood pressure using a pulse transit time corrected for vascular index

A method of monitoring a patient's blood pressure parameter, the method comprising:

• 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.

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 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.

A method of monitoring a patient's blood pressure parameter, the method comprising:

• 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.

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;
• 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.