Apparatus for blood pressure estimation using photoplethysmography and contact pressure
An apparatus for estimating cardiovascular information includes: a main body; and a strap connected to the main body and formed to be flexible to be wrapped around an object, wherein the main body may include: a pulse wave measurer configured to measure, from the subject, a first pulse wave signal by using a first light of a first wavelength, and a second pulse wave signal by using a second light of a second wavelength, the first wavelength being different from the second wavelength; a contact pressure measurer configured to measure a contact pressure between the object and the pulse wave measurer; and a processor configured to extract a cardiovascular characteristic value based on the first pulse wave signal, the second pulse wave signal, and change in the contact pressure, and estimate cardiovascular information based on the extracted cardiovascular characteristic value.
1. An apparatus for estimating cardiovascular information, the apparatus comprising:
a communication interface configured to receive, from an external device, a cardiovascular information estimation model;
a photoplethysmography (PPG) sensor configured to measure, from an object, a first pulse wave signal by using a first light of a first wavelength and a second pulse wave signal by using a second light of a second wavelength, the first wavelength being different from the second wavelength;
a force sensor configured to measure a contact pressure between the object and the PPG sensor; and
a processor configured to:
detect a contact pressure transition period in which the contact pressure continuously increases or the contact pressure continuously decreases;
extract a first valley point and a second valley point, respectively from a first derivative signal of the first pulse wave signal and a second derivative signal of the second pulse wave signal in the contact pressure transition period;
determine, as a cardiovascular characteristic value, a change in the contact pressure during a time period from a first point in time corresponding to the first valley point of the first derivative signal, to a second point in time corresponding to the second valley point of the second derivative signal; and
estimate blood pressure by inputting to the cardiovascular information estimation model that is received from the external device, the first valley point of the first derivative signal, the second valley point of the second derivative signal, and a rate of the change of the contact pressure over the time period from the first point in time and the second point in time that correspond to the first valley point of the first derivative signal and the second valley point of the second derivative signal, respectively.
2. The apparatus of claim 1 , wherein the PPG sensor comprises:
a light source configured to emit the first light and the second light onto the object; and
a photodetector configured to measure the first pulse wave signal and the second pulse wave signal by receiving the first light and the second light which are reflected or scattered from the object, respectively.
3. The apparatus of claim 1 , wherein the contact pressure transition period comprises a contact pressure increasing period during which the contact pressure continuously increases, and a contact pressure decreasing period during which the contact pressure continuously decreases.
4. The apparatus of claim 1 , wherein the processor is further configured to generate guide information for guiding a user to increase or decrease the contact pressure when the object is in contact with the force sensor.
5. The apparatus of claim 1 , further comprising an actuator configured to control the contact pressure between the object and the PPG sensor.
6. The apparatus of claim 1 , wherein the communication interface is further configured to transmit, to the external device, at least one of the first pulse wave signal and the second pulse wave signal.
7. The apparatus of claim 1 , further comprising an output interface configured to output the blood pressure to the external device.
8. The apparatus of claim 1 , wherein the apparatus is implemented in a cellular phone or a smartphone.