Patent ID: 9700255
Date: 2017-07-11
CPC Classifications: A61B

Claim:
1. A method of determining a consciousness level comprising: detecting an amplitude peak of a heart rate signal of a subject; calculating, using a processor, a heart rate interval between the amplitude peak of the heart rate signal and a previously detected amplitude peak of the heart rate signal; calculating, using the processor, a relation between frequency and spectral density by performing a frequency analysis on the heart rate interval; extracting, using the processor, upon detecting the amplitude peak of the heart rate signal at the detecting step, a combination of a maximum density that is a maximum among spectral densities that are calculated at the calculating a relation between frequency and spectral density step, a maximum frequency that is a frequency corresponding to the maximum density, and a magnitude difference relation that represents a difference between the maximum density and spectrum densities which correspond to frequencies adjoined to the maximum frequency; comparing, using the processor, the maximum frequency, the maximum density, and the magnitude difference relation to a maximum frequency, a maximum density, and a magnitude difference relation that are contained in a combination extracted at a previous timing of the detecting step; plotting, using the processor, the combination of the extracted maximum frequency and the extracted maximum density as a position on a consciousness level determination graph where the ordinate represents spectral density and abscissa represents frequency; dividing, using the processor, the area of the consciousness level determination graph, and allocating the divided areas with drowsiness levels; correcting, using the processor, the plotted position not such that the plotted position moves toward a positive end of the ordinate but such that the plot position moves toward an origin of the consciousness level determination graph; and determining, using the processor, the consciousness level by comparing the plotted extracted combination of maximum frequency and maximum density to the plotted combination extracted at the previous timing, where decreases in maximum frequency and maximum density of the extracted combination in comparison to the combination extracted at the previous timing indicates increasing drowsiness, and comparing the magnitude difference relation to the magnitude difference relation extracted at the previous timing, where decreases in the magnitude difference relation in comparison to the magnitude difference relation at the previous timing indicates the increasing drowsiness; and outputting the determination to a driver through a monitor and a speaker if the determination indicates increasing drowsiness.