System and Method for Measurement of Vital Signs of a Human

• US 20120108928A1
• Filed: 08/26/2011
• Published: 05/03/2012
• Est. Priority Date: 11/01/2010
• Status: Active Grant

• Current Assignee: Oxirate, Inc.
• Original Assignee: Oxirate, Inc.
• Inventors: Tverskoy, Boris
• Granted Patent: US 9,675,250 B2
• Time in Patent Office: Days
• US Class Current: 600/324
• CPC Class Codes: A61B 5/0059 using light, e.g. diagnosis by transillumination, diascopy, fluorescence A61B5/0093, A61B5/1455, A61B5/02416 and A61B5/0261 take precedence
• CPC Class Codes: A61B 5/02416 using photoplethysmograph signals, e.g. generated by infrared radiation A61B5/14552 takes precedence
• CPC Class Codes: A61B 5/1455 using optical sensors, e.g. spectral photometrical oximeters

Abstract

A method and system for optical measuring one or more vital signs of a human is described. The method includes generating an optical Pulse Width Modulated (PWM) signal modulated in accordance with a predetermined Pulse Width Modulation scheme. The PWM scheme includes one or more Pulse Width Modulations having different modulation frequencies. The method also includes applying the PWM optical signal to a measurement location in a blood perfused body tissue of the human and receiving light originated back from the measurement location. A photo current signal of a time response of the blood perfused body tissue to the PWM optical signal is indicative of the vital signs. The method includes generating a voltage signal from the photo current signal and processing the voltage signal for determining the vital signs.

Claims

1. A system for optical measuring at least one vital sign of a human, the system comprising:

(a) an optical transmitter including;

an optical emitter configured for generating and applying an optical signal to a measurement location in a blood perfused body tissue of the human, and

an optical signal driver including a pulse generator coupled to the optical emitter and configured for generating a series of electric pulses for driving the optical emitter by turning it “

on”

or “

off”

, thereby to provide a pulsed optical signal, and

(b) an optical receiver including;

an optical detector configured for receiving light originated back from at least a portion of the measurement location and generating a photocurrent signal including a time response of the blood perfused body tissue to said optical signal, said time response being indicative of said at least one vital sign, and

a bandwidth limiting unit coupled to the optical detector, having a predetermined gain and a predetermined bandwidth and configured for generating a voltage signal from photocurrent signal, said voltage signal being amplified to a desired gain level and having a desired band width; and

(c) a control system configured for

(i) adaptive control of said pulsed optical signal emitted by the optical transmitter by adjusting at least a width of said electric pulses driving the optical emitter such as to maintain said optical receiver in its non-saturated dynamic range; and

(ii) processing the voltage signal generated by said bandwidth limiting unit and determining said at least one vital sign.

2. The system of claim 1, wherein said control system includes:

a Pulse Width Modulator coupled to the optical signal driver and configured for said adjusting of the width of said electric pulses in accordance with a predetermined Pulse Width Modulation scheme; and

a signal analyzer arranged downstream of the bandwidth limiting unit and configured for the processing of said voltage signal generated by the bandwidth limiting unit, and for the determining of said at least one vital sign.

3. The system of claim 2, wherein said Pulse Width Modulation scheme includes a Pulse Width Modulation having a predetermined modulation frequency.

4. The system of claim 2, wherein said Pulse Width Modulation scheme includes at least two Pulse Width Modulations having different modulation frequencies.

5. The system of claim 2, wherein said Pulse Width Modulation scheme includes three Pulse Width Modulations having three different modulation frequencies.

6. The system of claim 4, wherein said series of electric pulses after said at least two Pulse Width Modulations comprises repetitive bursts of electric pulse samples, each burst having a predetermined burst duration time and a predetermined burst duty cycle, and each burst comprising a predetermined number of electric pulse samples having a predetermined sample width and a predetermined sample duty cycle.

7. The system of claim 5, wherein said series of electric pulses after said three Pulse Width Modulations comprises repetitive trains of bursts of electric pulse samples, each train of the bursts has a predetermined train duration time and train duty cycle and comprises a predetermined number of bursts having a predetermined burst duration time and a predetermined burst duty cycle, and each burst comprising a predetermined number of electric pulse samples having a predetermined sample width and a predetermined sample duty cycle.

8. The system of claim 1, wherein said optical emitter comprises at least one light source.

9. The system of claim 8, wherein said at least one light source operates at a wavelength in the range of 620 nm-1000 nm.

10. The system of claim 1, wherein said optical transmitter comprises a plurality of optical emitters activated either simultaneously or consequently.

11. The system of claim 1, wherein the optical detector comprises at least one photodiode.

12. The system of claim 2, wherein said bandwidth limiting unit has a bandwidth with a corner frequency below the highest Pulse Width Modulation frequency.

13. The system of claim 1, wherein said bandwidth limiting unit includes a transimpedance amplifier configured for amplifying and low pass filtering said photocurrent signal.

14. The system of claim 13, wherein said transimpedance amplifier includes an operational amplifier.

15. The system of claim 13, wherein said bandwidth limiting unit includes an additional low pass filter arranged downstream and coupled to the transimpedance amplifier.

16. The system of claim 15, wherein a cut-off frequency of the additional low pass filter is positioned between a frequency of the variation of the measured vital sign and the highest frequency of the Pulse Width Modulation.

17. The system of claim 13, wherein said bandwidth limiting unit includes a band pass filter arranged downstream and coupled to the transimpedance amplifier.

18. The system of claim 17, wherein said band pass filter has a center frequency equal to a second frequency of said at least two Pulse Width Modulations that is lower than the highest frequency.

19. The system of claim 2, wherein said signal analyzer includes a demodulator configured for processing the voltage signal generated by the bandwidth limiting unit for determining said at least one vital sign.

20. The system of claim 19, wherein said demodulator is a digital demodulator including A/D converter configured for converting the voltage signal generated by the bandwidth limiting unit from an analog form to a digital sampled form.

21. The system of claim 19, wherein said demodulator is an analog demodulator

22. The system of claim 2, wherein said control unit comprises a feedback controller coupled to the bandwidth limiting unit and to the Pulse Width Modulator.

23. The system of claim 22, wherein the feedback controller is (i) responsive to changes in a signal amplitude at an output of an amplifier of the bandwidth limiting unit, and (ii) configured to generate an amplifier gain control signal for controlling operation of the Pulse Width Modulator by adjusting at least said width of said electric pulses such as to maintain a gain level obtained at the output of the amplifier within an optimal range for operation of the amplifier.

24. The system of claim 22, wherein the feedback controller is (i) responsive to changes in a signal amplitude at an output of a band pass filter of the bandwidth limiting unit, and (ii) configured to generate a filter control signal for controlling operation of the Pulse Width Modulator by adjusting said width of said electric pulses such as to maintain the signal amplitude at said output of the band pass filter within an optimal range for operation of the band pass filter.

25. The system of claim 22, wherein the feedback controller is (i) responsive to changes of at least one modulation frequency of said predetermined Pulse Width modulation Scheme at an output of at least one unit of the bandwidth limiting unit selected from an amplifier, a low pass filter and a band pass filter;

and (ii) configured to generate frequency control signals in order to match the frequency characteristics of the amplifier, the low pass filter and/or the band pass filter.

26. The system of claim 22, wherein the feedback controller is (i) responsive to changes in a signal amplitude at an input of the demodulator, and (ii) configured to generate a detector control signal for controlling operation of the Pulse Width Modulator by adjusting said width of said electric pulses such as to maintain the demodulator within an optimal dynamic range for operation of the demodulator.

27. The system of claim 7, comprising a feedback controller coupled to the bandwidth limiting unit and to the Pulse Width Modulator, wherein said feedback controller is (i) responsive to said time response of the blood perfused body tissue to said optical signal, and (ii) configured to generate a measurement time interval control signal in order to adjust at least one modulation parameter selected from the train duration time and the train duty cycle to the variations of a heart rate of said human.

28. The system of claim 1, wherein said at least one vital sign of the human is selected from the list including a heart rate, a heart rate variability, an oxygen saturation, and a total blood hemoglobin.

29. A method for optical measuring at least one vital sign of a human, the method comprising:

generating an optical Pulse Width Modulated (PWM) signal modulated in accordance with a predetermined Pulse Width Modulation scheme;

applying the PWM optical signal to a measurement location in a blood perfused body tissue of the human;

receiving light originated back from at least a portion of the measurement location and generating a photo current signal of a time response of said blood perfused body tissue to said PWM optical signal, said time response being indicative of said at least one vital sign;

generating a voltage signal from said photo current signal; and

processing said voltage signal and determining said at least one vital sign.

30. The method of claim 29, wherein said Pulse Width Modulation scheme includes at least one Pulse Width Modulation having a predetermined modulation frequency.

31. The method of claim 30, wherein said Pulse Width Modulation scheme includes two Pulse Width Modulations having different modulation frequencies.

32. The method of claim 30, wherein said Pulse Width Modulation scheme includes three Pulse Width Modulations having three different modulation frequencies.

33. The method of claim 29, wherein said generating of the voltage signal includes amplifying said voltage signal to a desired gain level and filtering said voltage signal to a desired band width.

34. The method of claim 31, wherein said processing of said voltage signal includes:

converting the voltage signal from an analog form to a digital sampled form;

for several periods of the Pulse Width Modulation having a lower modulation frequency than the highest modulation frequency, calculating root mean square values of measured amplitudes of samples of the sampled voltage signal located in each period of said Pulse Width Modulation having the highest modulation frequency;

executing a discrete Fourier transform of said root mean square values over said several periods; and

determining a major harmonic of the variations of the root mean square values.

35. The method of claim 34, wherein said processing is carried out for a measurement at a wavelength corresponding to the red-near infrared spectral range, thereby obtaining a heart rate of the human indicated by said major harmonic.

36. The method of claim 34, wherein said processing is carried out for a measurement at two different wavelengths in the red band of light and in the infrared band of light, correspondingly.

37. The method of claim 36, comprising calculating a ratio of predetermined functions of the magnitudes of the major Fourier component of said root mean square values over said several periods for said two various wavelengths, thereby obtaining a blood oxygen saturation rate of the human.

38. The method of claim 32, wherein said generating of the optical Pulse Width Modulated (PWM) signal is carried out only during measurements intervals defined by the lowest modulation frequency of said three Pulse Width Modulations.

39. The method of claim 32, comprising adjusting at least a duty cycle of at least one modulation of said at least three Pulse Width Modulations.

40. The method of claim 39, comprising providing a feedback closed loop control for said adjusting of the duty cycle of said at least one modulation of said at least three Pulse Width Modulations.