MONITORING DEVICE AND METHOD FOR ESTIMATING BLOOD CONSTITUENT CONCENTRATION FOR TISSUES WITH LOW PERFUSION

摘要

The present disclosure concerns a method for estimating blood constituent concentration of a user under low perfusion conditions using a spectrophotometry-based monitoring device comprising a multichannel sensor (1) formed from a plurality of channels (2, 5), and a cardiovascular sensor (7, 14); comprising: measuring a plurality of photoplethysmographic (PPG) signals, each PPG signal being measured by one of the channels (2, 5); measuring a cardio-synchronous (CV) signal by using the cardiovascular sensor (7, 14); detecting a instantaneous heart rate and determining a heart rate variability from the CV signal; for each detected heart rate, projecting the measured PPG signals multiplied by a window function on a principal frequency component, and selecting reliable projected PPG signals; and estimating a value of said blood constituent concentration from the magnitude of said reliable projected PPG signals selected over a predetermined time period; wherein said window function has a window length which is adjusted at each detected heart rate according to the determined heart rate variability; and wherein the frequency of said principal frequency component is estimated by averaging the heart rate over the window length.The disclosed method requires diminished computational load compared to conventional methods based on frequency domain approach as FFT or DCT,and provides better time and frequency resolution and thus optimal noise reduction and minimal signal distortion.