Body-worn system for measuring continuous non-invasive blood pressure (cNIBP)
The present invention provides a technique for continuous measurement of blood pressure based on pulse transit time and which does not require any external calibration. This technique, referred to herein as the ‘Composite Method’, is carried out with a body-worn monitor that measures blood pressure and other vital signs, and wirelessly transmits them to a remote monitor. A network of body-worn sensors, typically placed on the patient's right arm and chest, connect to the body-worn monitor and measure time-dependent ECG, PPG, accelerometer, and pressure waveforms. The disposable sensors can include a cuff that features an inflatable bladder coupled to a pressure sensor, three or more electrical sensors (e.g. electrodes), three or more accelerometers, a temperature sensor, and an optical sensor (e.g., a light source and photodiode) attached to the patient's thumb.
1. A system for monitoring a patient's blood pressure, the system comprising:
a pressure-delivery system for applying a variable pressure to the patient's arm;
a pressure sensor for measuring a time-dependent pressure waveform representing the pressure applied to the patient's arm;
a first sensor configured to attach to the patient and generate a first time-dependent waveform representing a flow of blood within the patient;
a second sensor configured to attach to the patient and generate a second time-dependent waveform representing contractile properties of the patient's heart; and,
a processing component programmed to: i) determine an index pulse transit time (PTT index ) from a separation in time of a first feature of the first time-dependent waveform and a second feature of the second time-dependent waveform; ii) process the pressure, first, and second waveforms as pressure is applied by the pressure-delivery system and determine therefrom a patient-specific slope (m femoral ) representing a relationship between pulse transit time and mean arterial blood pressure in the patient's femoral artery; iii) determine a mean arterial pressure value (MAP INDEX ) from a peak pulse amplitude in the time-dependent pressure waveform; and iv) determine a mean blood pressure value in the patient's femoral artery (MAP femoral ) from a pulse transit time measured from the first and second waveforms (PTT) according to the equation MAP femoral =(m femoral ×PTT)−(m femoral ×PTT INDEX )+MAP INDEX , wherein PTT INDEX represents a pulse transit time determined before PTT.
2. The system of claim 1 , wherein the processing component is programmed to determine m femoral by collectively processing the first, second, and pressure waveforms.
3. The system of claim 2 , wherein the processing component is programmed to determine m femoral by processing a set of pulse transit time values measured while time-dependent pressure is applied to the patient's arm.
4. The system of claim 3 , wherein the processing component is programmed to determine m femoral by fitting the set of pulse transit time values to a linear equation.