Photoplethysmography (PPG) device and the method thereof

• US 20050058456A1
• Filed: 07/07/2004
• Published: 03/17/2005
• Est. Priority Date: 07/07/2003
• Status: Active Grant

• Current Assignee: Silicon Mitus, Inc.
• Original Assignee: Sun Kook Yoo
• Inventors: Yoo, Sun Kook
• Granted Patent: US 7,336,982 B2
• Time in Patent Office: Days
• US Class Current: 398/140
• CPC Class Codes: A61B 5/14551 for measuring blood gases
• CPC Class Codes: A61B 5/7207 of noise induced by motion artifacts

Abstract

A method of measuring Photoplethysmography (PPG) signals may comprise detecting dual wavelength illumination from a light detector so as to provide detected signals, converting the detected signals into digital signals so as to provide digital signals, reducing noises from the digital signals and increasing independency between the digital signals so as to provide preprocessed signals, subtracting the average value from the preprocessed signals so as to provide adjusted signals, obtaining whitening matrix based on covariance, eigen value, and eigen matrix obtained from the adjusted signals, and restoring data using the whitening matrix.

Claims

1. The method to measure Photoplethysmography(PPG) signals comprising the steps wherein;

(a) a light detecting step to detect dual wavelength illumination from a light detector;

(b) A/D conversion step, converting the said detected analog signals into digital ones;

(c) preprocessing step reducing noises from the each of outputs from the said A/D conversion step, and to increase independence between the signals;

(d) centering process step to subtract the average value from the said outputs of preprocessing step;

(e) whitening process step to drive out whitening matrix, by calculating covariance, it'"'"'s eigen value and eigen matrix from the outputs of the said centering process step;

(f) data restoring step to restore data from the output of whitening process setp.

3. The method as claimed in claim 1 or claim 2, wherein the preprocessing step includes steps of;

(a) period measuring step to drive out the period of Photoplethysmography(PPG) signals, from the output of the said A/D conversion step, using autocorrelation;

(b) interleaving process step, to relocate data in a given sequence of amplitude according to the said calculated period;

(c) time low-pass filtering step to transform over the all sampling points into the average value of current point, previous point, and next point;

(d) the innovation process step to subtract the average up to the previous value, from current output of the said time low-pass filtering step.

2. The method to measure Photoplethysmography(PPG) signals comprising the steps wherein;

(a) light detecting step to detect dual wavelength illumination from a light detector;

(b) A/D conversion step, converting the said detected analog signals into digital ones;

(c) preprocessing step reducing noises from the each of outputs from the said A/D conversion step, and to increase independence between the signals;

(d) centering process step to subtract the average value from the said outputs of preprocessing step;

(e) whitening process step to drive out whitening matrix, by calculating covariance, it'"'"'s eigen value and eigen matrix from the outputs of the said centering process step;

(f) calculating step for the matrix W, to calculate out a demixing matrix W, repeatedly adopting the contrast Gaussian function;

(g) calculating step for a mixing matrix A, to calculate out using the outputs from the said whitening process step and the said calculating step for the matrix W;

(h) data restoring step to restore data using the said calculating step for the matrix W and the said calculating step for the matrix A.

4. The method as claimed in claim 2, wherein the data restoring step includes steps of;

(a) step to decide Photoplethysmography(PPG) signal between separated Photoplethysmography(PPG) signal and noise signal using demixing matrix W, and then restore the sign and gain of measured Photoplethysmography(PPG) signal using the mixing matrix A;

(b) calculating step to calculate the ratio R of the normalized transmitted amount of red and infrared lights, from the said matrix A;

(c) the step calculating the arterial oxygen saturation (SpO₂), using the said R, by the given formula.

arterial oxygen saturation (SpO₂)(%)=a−

bR,

(where, 107≦

a≦

110, 25≦

b≦

32)

5. The Photoplethysmography(PPG) measuring device comprising the elements of;

(a) light emitting unit composed of two LEDs(light emitting diodes) to emit dual beams of different wavelengths, and a driving circuit for said LEDs;

(b) light detector unit to transform the said transmitted or reflected lights of dual wave lengths, into electrical signals;

(c) input separating circuit to amplify the output from the said the light detector unit, and to reduce ambient artifact;

(d) A/D converter unit to convert the output analog signals from the said input separating circuit, into digital signals;

(e) digital signal processing unit to reduce motion artifact from the output of the said A/D converter unit;

(f) computer unit to evaluate, store, and display the received output signal from the said digital signal processing unit.

6. The device as claimed in claim 5;

the communication between the said digital signal processing unit and the said computer unit, to transmit the output from the said digital signal processing unit to the said computer unit, is performed through wireless channel.

7. The device as claimed in claim 5;

the communication between the said digital signal processing unit and the said computer unit, to transmit the output from the said digital signal processing unit to the said computer unit, is performed through wire channel.