Methods and apparatus for physiological measurement using color band photoplethysmographic sensor
In illustrative implementations of this invention, a photoplethysmographic device measures variations of light that is reflected from, or transmitted through, human skin. In some implementations, the device includes a camera that takes the measurements remotely. In others, the device touches the skin during the measurements. The device includes a camera or other light sensor, which includes at least orange, green and cyan color channels. In some cases, such as a contact device, the device includes three or more colors of active light sources, including at least orange, green and cyan light sources. A computer analyzes the sensor data, in order to estimate a cardiac blood volume pulse wave. For each cardiac pulse, a computer detects the systolic peak and diastolic inflection of the wave, by calculating a second derivative of the wave. From the estimated wave, a computer estimates heart rate, heart rate variability and respiration rate.
1. Apparatus comprising a photoplethysmograph, which photoplethysmograph includes at least five color channels, which color channels include an orange color channel, a green color channel and a cyan color channel.
2. The apparatus of claim 1 , wherein the color channels further include a red color channel and a blue color channel.
3. The apparatus of claim 1 , wherein each of the color channels comprises a set of pixels in a video camera.
4. The apparatus of claim 1 , wherein the photoplethysmograph is housed in a housing, which housing is configured to touch tissue while a camera in the photoplethysmograph captures light that reflects from, or is transmitted through, the tissue.
5. The apparatus of claim 4 , wherein the photoplethysmograph includes at least three light sources, including an orange light source, a green light source, and a cyan light source.
6. The apparatus of claim 1 , wherein the photoplethysmograph includes at least three light sources, including an orange light source, a green light source, and a cyan light source.
7. A method comprising, in combination:
(a) taking measurements of light that reflects from, or is transmitted through, tissue of a mammal; and
(b) taking, as input, data indicative of the measurements, and estimating a blood pulse volume wave; wherein the measurements are taken by at least five color channels of a light sensor, which color channels include an orange color channel, a green color channel and a cyan color channel.
8. The method of claim 7 , wherein the measurements are taken by at least five color channels of the light sensor, which at least five color channels include at least an orange color channel, a green color channel, a cyan color channel, a red color channel and a blue color channel.
9. The method of claim 7 , further comprising estimating a time interval between a systolic peak and a diastolic inflection, which peak and inflection occur during a single heartbeat of the blood pulse volume wave.
10. The method of claim 9 , further comprising calculating a second derivative of the blood pulse volume wave.
11. The method of claim 7 , wherein the light sensor comprises a digital video camera.
12. The method of claim 11 , wherein the camera is positioned more than a meter from the tissue while the measurements are taken.
13. The method of claim 7 , wherein the light sensor is housed in a housing, which housing does not touch the tissue while the measurements are taken.
14. The method of claim 7 , further comprising calculating a heart rate of the mammal.
15. Apparatus comprising, in combination:
(a) a set of light sensors for taking measurements of light that reflects from, or is transmitted through, tissue of a mammal; and
(b) one or more computer that are programmed to take, as input, data indicative of the measurements, and to estimate a blood pulse volume wave; wherein the light sensors include at least five color channels, which color channels include an orange color channel, a green color channel and a cyan color channel.
16. The apparatus of claim 15 , wherein the light sensors comprise pixels in a digital video camera.
17. The apparatus of claim 15 , wherein the color channels further include a red color channel and a blue color channel.
18. The apparatus of claim 15 , wherein the light sensors are housed in a housing, which housing is configured to touch tissue while the light sensors capture light that reflects from, or is transmitted through, the tissue.
19. The apparatus of claim 18 , wherein the housing also houses at least three light sources, including an orange light source, a green light source, and a cyan light source.