Body-worn system for continuous, noninvasive measurement of vital signs

Abstract

The invention provides methods and systems for continuous noninvasive measurement of vital signs such as blood pressure (cNIBP) based on pulse arrival time (PAT). The invention uses a body-worn monitor that recursively determines an estimated PEP for use in correcting PAT measurements by detecting low frequency vibrations created during a cardiac cycle, and a state estimator algorithm to identify signals indicative of aortic valve opening in those measured vibrations.

What is claimed is: 
     
         1 . A system for obtaining a continuous measurement of cardiac pre-ejection period for an individual, comprising:
 an ECG sensor configured to be worn on the patient's body and detect signals indicative of electrical activity of the individual's heart for time n, filter the signals using a 60 Hz notch filter, digitize the filtered signals, generate therefrom a time-dependent electrocardiogram waveform, and transmit the time-dependent electrocardiogram waveform as packet data;   a seismocardiogram sensor configured to be worn on the patient's body and detect signals indicative of compression waves produced due to contraction of the individual's heart for time n, filter the signals using a 5 and 35 Hz bandpass filter, digitize the filtered signals, generate therefrom a time-dependent seismocardiogram waveform, transmit the time-dependent seismocardiogram waveform as packet data; and   a plethysmogram sensor apparatus configured to be worn on the patient's body and detect signals indicative of changes in blood volume at an extremity produced due to contraction of the individual's heart for time n and generate therefrom a time-dependent plethysmogram waveform.   a processing apparatus operably connected to the ECG sensor, the seismocardiogram sensor, and the plethysmogram sensor, the processing apparatus configured to receive the time-dependent electrocardiogram waveform transmitted by the ECG sensor, the time-dependent seismocardiogram waveform transmitted by the seismocardiogram sensor, and the time-dependent plethysmogram waveform, and to
 (i) time synchronize the time-dependent electrocardiogram waveform, the time-dependent seismocardiogram waveform, and the time-dependent plethysmogram waveform, 
 (ii) recursively determine the occurrence of aortic valve opening for each contraction c of the individual's heart during time n by processing a portion of the time-dependent seismocardiogram waveform within a moving time window of length l comprising a plurality of contractions of the individual's heart which includes contraction c to provide an averaged seismocardiogram waveform corresponding to contraction c, and identifying a first fiducial point indicating opening of the aortic valve for contraction c in the averaged seismocardiogram waveform, 
 (iii) recursively determine a pre-ejection period (PEP) for each contraction c of the individual's heart during time n by determining a time difference between a second fiducial point in the time-dependent electrocardiogram waveform indicating the onset of electrical stimulation of the ventricles during contraction c and the first fiducial point indicating opening of the aortic valve for contraction c, 
 (iii) recursively calculate an average pre-ejection period (m PEP ) every m seconds from the PEPs determined for each contraction c during a time window w immediately preceding calculating m PEP , wherein m is between 1 and 10 seconds, and w is between 15 seconds and 3 minutes, wherein a median of the PEPs (MED PEP ) and a variance of the PEPs (σ 2   PEP ) within time window w are calculated, and PEPs determined for each contraction c during time window w which differ from PEP MED  by more than 2σ are discarded prior to calculating m PEP , 
 (iii) recursively determine a Pulse Arrival Time (PAT) for each contraction c of the individual's heart during time n by determining a time difference between the second fiducial point in the time-dependent electrocardiogram waveform indicating the onset of electrical stimulation of the ventricles during contraction c and a third fiducial point in the time-dependent plethysmogram waveform indicating arrival of the pressure wave at the extremity due to contraction c, 
 recursively calculating an average PAT (m PAT ) every p seconds from the PATs determined for each contraction c during a time window q, wherein p is between 1 and 10 seconds, and q is between 15 seconds and 3 minutes, wherein a median of the PATs (MED PAT ) and a variance of the PATs (σ 2   PAT ) within time window q are calculated, and PATs determined for each contraction c during time window q which differ from MED PAT  by more than 2σ are discarded prior to calculating m VTT , 
 recursively calculating a vascular transit time (VTT) for each contraction c during time n by subtracting m PEP  at time t from m PAT  at time t, and calculating a blood pressure value using the VTT. 
   
     
     
         2 . A system according to  claim 1 , wherein the processing apparatus is further configured to recursively determine an estimated time of aortic valve closure for each contraction c of the individual's heart during time n. 
     
     
         3 . A system according to  claim 1 , wherein the processing apparatus is further configured to recursively determine an estimated time of mitral valve closure for each contraction c of the individual's heart during time n. 
     
     
         4 . A system according to  claim 1 , wherein time n is at least one hour. 
     
     
         5 . A system according to  claim 1 , wherein the length of the moving window is between 15 seconds and 2 minutes.