Tissue variability compensation apparatus and method

• US 10,390,717 B2
• Filed: 11/30/2016
• Issued: 08/27/2019
• Est. Priority Date: 05/30/2014
• Status: Active Grant

• Current Assignee: Huntleigh Technology, Inc.
• Original Assignee: Huntleigh Technology, Inc.
• Inventors: Cook, Stephen John, Baily, Francis Gregory, Morris, Philip, Gough, Nigel A J
• Primary Examiner(s): Kuan, John C
• Application Number:
  US15/365,635
• Publication Number:
  US 20170079536A1
• Time in Patent Office: 1,000 Days
• Field of Search: None
• CPC Class Codes: A61B 2562/0233 Special features of optical sensors or probes classified in A61B5/00
• CPC Class Codes: A61B 5/0017 transmitting optical signals transmission by light H04B10/00
• CPC Class Codes: A61B 5/02007 Evaluating blood vessel condition, e.g. elasticity, compliance
• CPC Class Codes: A61B 5/02416 using photoplethysmograph signals, e.g. generated by infrared radiation A61B5/14552 takes precedence
• CPC Class Codes: A61B 5/02433 for infrared radiation
• CPC Class Codes: A61B 5/14551 for measuring blood gases
• CPC Class Codes: A61B 5/1495 Calibrating or testing of in-vivo probes
• CPC Class Codes: A61B 5/6828 Leg
• CPC Class Codes: A61B 5/7203 for noise prevention, reduction or removal
• CPC Class Codes: A61B 5/7214 using signal cancellation, e.g. based on input of two identical physiological sensors spaced apart, or based on two signals derived from the same sensor, for different optical wavelengths
• CPC Class Codes: A61B 5/7225 Details of analog processing, e.g. isolation amplifier, gain or sensitivity adjustment, filtering, baseline or drift compensation A61B5/30, A61B5/316 take precedence; transformers for specific applications H01F38/00; amplifiers H03F
• CPC Class Codes: A61B 5/7228 Signal modulation applied to the input signal sent to patient or subject; demodulation to recover the physiological signal modulation H03C
• CPC Class Codes: A61B 5/725 using specific filters therefor, e.g. Kalman or adaptive filters A61B5/316 take precedence
• CPC Class Codes: A61B 5/7257 using Fourier transforms
• CPC Class Codes: G16H 40/63 for local operation

Abstract

A method and apparatus of compensating for a differential error between a plurality of body surface sensors, where each sensor respectively comprises a transmitter and a receiver.

Claims

1. An apparatus for compensating for a differential error between a plurality of body surface sensors for acquiring respective physiological signals from a human or animal patient, each such sensor respectively comprising a transmitter, a receiver, and a charge-to-voltage converter connected to an output of the respective receiver, the apparatus comprising:

a timing signal generator comprising an oscillator, to generate a timing signal;

a channel for each respective body surface sensor, the channel comprising;

(i) a current modulator to receive said timing signal and supply a current drive signal timed by said timing signal to the transmitter of the respective body surface sensor;

(ii) a synchronous receiver to receive said timing signal from the timing signal generator and an output signal timed by said timing signal from the charge-to-voltage converter of the respective body surface sensor and supply a broadband output signal;

(iii) an analogue high-pass filter to receive the broadband output signal from the synchronous receiver and supply a filtered output signal; and

(iv) an anti-aliasing analogue low-pass filter to receive the filtered output signal from the high-pass filter and supply an anti-aliased output signal;

the apparatus further comprising;

an analogue-to-digital converter to receive the anti-aliased output signal from the respective channel of each respective body surface sensor and supply a digital output signal for downstream signal processing;

wherein the timing signal generator also generates a digital representation of a sine wave and comprises a digital-to-analogue converter to receive the digital sine wave representation at an update rate higher than a frequency of the timing signal and convert the digital sine wave representation into an analogue sine wave having a frequency greater than a highest frequency of the physiological signals and less than a cut-off frequency of the anti-aliasing low pass filter;

a low-pass filter to receive the analogue sine wave from the digital-to-analogue converter and remove update rate components therefrom to provide a clean sine wave; and

an amplitude modulator to receive the clean sine wave from the low-pass filter and add the clean sine wave to the timing signal.

2. An apparatus according to claim 1, wherein the oscillator is a crystal with a natural frequency substantially equal to 4 MHz.

3. An apparatus according to claim 1, wherein the timing signal generator generates a timing signal with a frequency of from 500 to 1500 Hz.

4. An apparatus according to claim 1, wherein the timing signal generator generates a timing signal with a frequency of from 500 to 1500 Hz.

5. An apparatus according to claim 1, wherein the timing signal generator generates a timing signal with a frequency substantially equal to 1 kHz.

6. An apparatus according to claim 1, wherein the analogue high-pass filter is a two-pole, Sallen-Key filter providing 3 dB at about 0.07 Hz.

7. An apparatus according to claim 1, wherein the anti-aliasing analogue low-pass filter is a two-pole, Sallen-Key filter providing 3 dB at about 6 Hz.

8. An apparatus according to claim 1, wherein the update rate is substantially equal to 20.48 kHz.

9. An apparatus according to claim 1, wherein the low-pass filter is a single-pole, R-C filter providing −

3 dB at about 20 Hz.

10. An apparatus according to claim 1, further comprising the plurality of body surface sensors.

11. An apparatus according to claim 10, wherein the transmitter is a gallium aluminium arsenide infrared optical transmitter radiating energy at a wavelength substantially equal to 890 nm, and the receiver is an infrared optical receiver in the form of a silicon PIN photodiode with a response in the range of from 750 to 1100 nm.

12. A method of compensating for a differential error between a plurality of body surface sensors, where each of the plurality of body surface sensors respectively comprises a transmitter and a receiver, the method comprising:

adding an amplitude modulated signal to a transmitted signal respectively transmitted by each of said transmitters, the amplitude modulated signal having a frequency;

(i) greater than a highest frequency of a physiological signal of a human or animal patient to which the plurality of body surface sensors is applied; and

(ii) less than a cut-off frequency of an anti-aliasing low pass filter of an apparatus for processing a received signal respectively received by each of said receivers;

applying a band-pass filter to recover the amplitude modulated signal from a plurality of the received signals to provide a respective plurality of compensation signals;

comparing respective amplitudes of the respective plurality of compensation signals with each other; and

adjusting an amplitude of at least one of the respective received signals until the amplitudes of the respective plurality of compensation signals are substantially equal to each other.

13. A method according to claim 12, wherein the frequency of the amplitude modulated signal is greater than a second harmonic of a heartbeat of the human or animal patient.

14. A method according to claim 12, wherein the frequency of the amplitude modulated signal is from 3 to 7 Hz.

15. A method according to claim 12, wherein the frequency of the amplitude modulated signal is from 4 to 6 Hz.

16. A method according to claim 12, wherein the frequency of the amplitude modulated signal is substantially equal to 5 Hz.