Heart rate monitor

Abstract

A wrist worn heart rate monitor includes a photoplethysmogram (PPG) sensor and an inertial sensor. Signals from the inertial sensor are used to identify and remove noise from the PPG signals. An initial heart rate value is selected from a number of heart rate candidates that remain in the resulting PPG spectrum and is used to track the heart rate of the user. The PPG spectrum is monitored while tracking the heart rate to determine if the selected initial heart rate value is in error. The PPG spectrum may be monitored by determining a correlation of possible heart rate candidates in each PPG spectrum to the previous heart rate candidates and resetting the heart rate value accordingly. Additionally or alternatively, the PPG spectrum may be monitored by determining when only a single heart rate candidate is present in consecutive PPG spectra and resetting the heart rate value accordingly.

What is claimed is: 
     
         1 . A method for monitoring a heart rate, the method comprising:
 receiving photoplethysmogram (PPG) signals from a PPG sensor worn by a user;   receiving inertial sensor signals from an inertial sensor worn by the user;   windowing the PPG signals and the inertial sensor signals;   generating a PPG spectrum and an inertial data spectrum for each window of the PPG signals and inertial sensor signals;   eliminating peaks in each PPG spectrum using the inertial data spectrum from a corresponding window;   selecting one of multiple peaks in a PPG spectrum as an initial value of the heart rate of the user;   tracking the heart rate of the user based on the initial value of the heart rate;   selecting one of multiple peaks in the PPG spectrum as an initial value of the heart rate of the user;   tracking the heart rate of the user based on the initial value of the heart rate;   monitoring each new PPG spectrum for an occurrence of a single peak while continuing to track the heart rate of the user based on the one of multiple peaks that is selected;   selecting the single peak when the single peak occurs in consecutive PPG spectra as a new value of the heart rate; and   tracking the heart rate of the user based on the new value of the heart rate.   
     
     
         2 . The method of  claim 1 , wherein generating the PPG spectrum and the inertial data spectrum comprises converting a time domain representation of PPG signals for each window into a frequency domain representation using a Fast Fourier Transform and converting a time domain representation of inertial sensor signals for each window into a frequency domain representation using the Fast Fourier Transform. 
     
     
         3 . The method of  claim 1 , further comprising performing blind source separation on the PGG signals in a time domain using the inertial data spectrum and the PPG spectrum to reduce a number of the remaining peaks to produce a subset of the remaining peaks, wherein the initial value of the heart rate is selected from the subset of the remaining peaks. 
     
     
         4 . The method of  claim 1 , wherein the PPG sensor and the inertial sensor are worn on a wrist of the user. 
     
     
         5 . The method of  claim 1 , wherein the inertial sensors are accelerometers. 
     
     
         6 . The method of  claim 1 , wherein selecting the single peak when the single peak occurs in consecutive PPG spectra comprises selecting the single peak when the single peak occurs in at least five consecutive PPG spectra. 
     
     
         7 . The method of  claim 1 , further comprising determining a heart rate trend and a physical activity trend rate and using them to determine if the heart rate is correct.