A pulse wave represents a change in the volume of blood, and therefore, a photoelectric pulse wave sensor can measure the pulse wave by capturing the change in the volume of blood in a site to be measured. However, the volume of blood in a portion to be measured also changes due to movement (hereinafter, referred to as body motion) of a human body in addition to pulsation (that is, pulse wave) of the heart. For this reason, at the time of measuring a pulse wave using the photoelectric pulse wave sensor, in some cases, a noise due to body motion is included in wave motion in the process of propagation of the pulse wave from the heart to a site to be measured. That is, blood is a fluid and blood vessels are elastic, and therefore, in some cases, the flow of blood, which is caused by body motion, causes a change in the volume of blood and is measured as pseudo pulsation.
A pulse wave measuring device which performs calculation processing in order to remove a noise component due to such body motion has been developed. For example, PTL 1 discloses a technique of emitting light having different wavelengths, measuring reflected light thereof at the same time, and extracting a pulsation component from the measured value. This technique uses the fact that there are different extinction characteristics between oxygenated hemoglobin which is dominant in arterial blood and reduced hemoglobin which is dominant in venous blood.
USPTO Backgrounds
USPTO Backgrounds