MONITORING DEVICE AND METHOD FOR ESTIMATING BLOOD CONSTITUENT CONCENTRATION FOR TISSUES WITH LOW PERFUSION

• US 20120190948A1
• Filed: 02/28/2012
• Published: 07/26/2012
• Est. Priority Date: 09/03/2009
• Status: Active Grant

• Current Assignee: CSEM Centre Suisse d'Electronique et de Microtechnique SA Recherche et Développement, CSEM SA
• Original Assignee: CSEM SA
• Inventors: Vetter, Rolf, Rossini, Leopoldo, Ridolfi, Andrea, Sola i Caros, Josep, Correvon, Marc
• Granted Patent: US 9,687,162 B2
• Time in Patent Office: Days
• US Class Current: 600/324
• CPC Class Codes: A61B 2562/0219 Inertial sensors, e.g. accelerometers, gyroscopes, tilt switches
• CPC Class Codes: A61B 2562/0233 Special features of optical sensors or probes classified in A61B5/00
• CPC Class Codes: A61B 2562/046 in a matrix array
• CPC Class Codes: A61B 5/0205 Simultaneously evaluating both cardiovascular conditions and different types of body conditions, e.g. heart and respiratory condition
• CPC Class Codes: A61B 5/02405 Determining heart rate variability
• CPC Class Codes: A61B 5/02416 using photoplethysmograph signals, e.g. generated by infrared radiation A61B5/14552 takes precedence
• CPC Class Codes: A61B 5/0245 by using sensing means generating electric signals, i.e. ECG signals
• CPC Class Codes: A61B 5/14552 Details of sensors specially adapted therefor
• CPC Class Codes: A61B 5/721 using a separate sensor to detect motion or using motion information derived from signals other than the physiological signal to be measured
• CPC Class Codes: A61B 5/7221 Determining signal validity, reliability or quality A61B5/7207 and A61B5/7217 take precedence
• CPC Class Codes: A61B 5/7257 using Fourier transforms

Abstract

The present disclosure relates to a method for estimating blood constituent concentration of a user under low perfusion conditions using a spectrophotometry-based monitoring device; the method comprising: measuring a plurality of photoplethysmographic (PPG) signals; measuring a cardio-synchronous (CV) signal; detecting an instantaneous heart rate and determining a heart rate variability from the CV signal; selecting reliable projected PPG signals; estimating a value of said blood constituent concentration from the magnitude of said reliable projected PPG signals. The disclosed method requires diminished computational load compared to conventional methods based on frequency domain approach as FFT or DCT. The disclosure also pertains to a monitoring device for estimating blood constituent concentration in tissue under low perfusion of a user.

Claims

1. Method for estimating blood constituent concentration of a user under low perfusion conditions using a spectrophotometry-based monitoring device comprising a multichannel sensor formed from a plurality of channels, and a cardiovascular sensor;

comprising;

measuring a plurality of photoplethysmographic (PPG) signals, each PPG signal being measured by one of the channels;

measuring a cardio-synchronous(CV) signal by using the cardiovascular sensor;

detecting an instantaneous heart rate and determining a heart rate variability from the CV signal;

for each detected heart rate, projecting the measured PPG signals multiplied by a window function on a principal frequency component, and selecting reliable projected PPG signals; and

estimating a value of said blood constituent concentration from the magnitude of said reliable projected PPG signals selected over a predetermined time period;

said window function having a window length which is adjusted at each detected heart rate according to the determined heart rate variability; and

the frequency of said principal frequency component being estimated by averaging the heart rate over the window length.

2. The method according to claim 1, wherein said blood constituent concentration comprises blood oxygen saturation, carboxyhemoglobin, met-hemoglobin, or a combination of any of them.

3. The method according to claim 1, wherein the principal frequency component is a harmonic component with its phase being determined by the instantaneous heart rate and with its frequency being determined by the averaged heart rate.

4. The method according to claim 1, wherein the principal frequency component is a wavetable oscillator with its phase being determined by the instantaneous heart rate and with its frequency being determined by the averaged heart rate.

5. The method according to claim 1, wherein said averaging the heart rate comprises determining the mean heart rate value of heart rate detected prior to the instantaneous heart rate, over the whole window length.

6. The method according to claim 1, wherein said selecting reliable projected PPG signals comprises selecting projected PPG signals having a predetermined magnitude and a predetermined phase and/or coherence between the PPG signals and the principal frequency component.

7. The method according to claim 6, wherein said predetermined coherence is equal or above 0.7.

8. The method according to claim 1, wherein the monitoring device further comprises a motion sensor or measuring a motion signal, and wherein

the method further comprises extracting a motion frequency from the motion signal.

9. The method according to claim 8, wherein the window function is designed according to the extracted motion frequency.

10. The method according to claim 9, wherein for the motion artifacts being smaller than large-band background noise, the window function has maximal attenuation of lateral lobes.

11. The method according to claim 10, wherein the window function is a Hanning window or a Kaiser window.

12. The method according to claim 11, wherein for the motion artifacts being larger than large-band background noise, the window function yields an equivalent frequency response having zeros at the motion frequency and its harmonics.

13. The method according to claim 12, wherein the window function is a rectangular window.

14. Monitoring device for estimating blood constituent concentration in tissue under low perfusion of a user comprising a multichannel sensor formed from a plurality of channels for delivering photoplethysmographic (PPG) signals;

and a cardiovascular sensor for delivering a cardio-synchronous (CV) signal.

15. The monitoring device according to claim 14, further comprising a motion sensor for measuring a motion signal.

16. The monitoring device according to claim 14, wherein each of said plurality of channels comprises an emitter containing a first and second radiation source emitting at the red and infrared wavelengths, respectively, and a receiver for receiving optical radiation emitted by the emitter.

17. The monitoring device according to claim 14, wherein said cardiovascular sensor is an ECG sensor and the CV signal is a surface ECG signal.

18. The monitoring device according to claims 14, wherein

said cardiovascular sensor is an ECG sensor and the CV signal is a PPG signal.