MONITORING A VITAL PARAMETER OF A PATIENT WITH "IN-SITU" MODULATION SCHEME TO AVOID INTERFERENCE

• US 20110092824A1
• Filed: 06/09/2009
• Published: 04/21/2011
• Est. Priority Date: 06/16/2008
• Status: Active Grant

• Current Assignee: Koninklijke Philips N.V.
• Original Assignee: Koninklijke Philips Electronics N.V. (Koninklijke Philips N.V.)
• Inventors: Veen, Jeroen, Jansen, Theodorus Petrus Henricus Gerardus, Verberne, Henricus Renatus Martinus, Schenk, Tim Corneel Wilhelmus, Feri, Lorenzo
• Granted Patent: US 8,447,372 B2
• Time in Patent Office: Days
• US Class Current: 600/477
• 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 5/14551 for measuring blood gases

Abstract

The invention relates to a method of monitoring a vital parameter of a patient by measuringattenuation of light emitted onto tissue of the patient, comprising the following steps: modulating the light with a modulation frequency or/and a modulation code; emitting the modulated light onto the tissue of the patient; collecting lightwhich is transmitted through the tissue or/and which is reflected from the tissue; demodulating the collected light; analyzing the demodulated collected light with regard to interference with ambient light; determining amodulation frequency or/and a modulation code for which interference with the ambient light is minimized or falls under a predefined threshold; and setting the modulation frequency or/and the modulation code for modulating the light according to the determined modulation frequency or/and a modulation code for which interference with the ambient light is minimized or falls under a predefined threshold. In this way a versatile and reliable possibility of monitoring a vital parameter of a patient with a high signal-to-interference ratio is provided.

Claims

1. A method of monitoring a vital parameter of a patient by measuring attenuation of light emitted onto tissue of the patient, comprising the following steps:

modulating the light according to a modulation mode;

emitting the modulated light onto the tissue of the patient;

collecting ambient light and/or light which is transmitted through the tissue and/or light which is reflected from the tissue;

demodulating the collected light according to the modulation mode;

analyzing the demodulated collected light with regard to the contribution of the ambient light;

determining a modulation mode for which the contribution of the ambient light is minimized or falls under a predefined threshold; and

setting the modulation mode for modulating the light according to the determined modulation mode for which the contribution of the ambient light is minimized or falls under a predefined threshold.

2. The method according to claim 1, wherein the modulation mode is a modulation frequency or/and a modulation code.

3. The method according to claim 2, wherein the step of emitting light onto the tissue of the patient is interrupted for a predefined interruption time period,

during this interruption time period the collected light is successively demodulated with different modulation frequencies, and

the modulation frequency for which the output of demodulating the collected light is minimized or falls under a predefined threshold is determined to be the modulation frequency for the light emitted onto the tissue of the patient after the predefined interruption time period.

4. The method according to claim 3, wherein the different modulation frequencies are a discrete set of frequencies or are continuous within a predefined range.

5. The method according to claim 2, wherein the step of emitting light onto the tissue of the patient is interrupted for a predefined interruption time period,

during this interruption time period the collected light is successively demodulated with different modulation codes, and

the modulation code for which the output of demodulating the collected light is minimized or falls under a predefined threshold is determined to be the modulation code for the light emitted onto the tissue of the patient after the predefined interruption time period.

6. The method according to claim 5, wherein in the case that the step of analyzing the demodulated collected light with regard to the contribution of the ambient light yields a lower level of contribution, a shorter modulation code is applied;

and in the case that the step of analyzing the demodulated collected light with regard to contribution of the ambient light yields a higher level of contribution, a longer modulation code is applied.

7. The method according to claim 2, wherein the step of emitting light onto the tissue of the patient is interrupted for a predefined interruption time period,

during this interruption time period the power spectrum of the collected light is determined using a Fourier transform, and

the frequency for which the power spectrum is determined to have its minimum or a frequency for which the power spectrum falls below a predefined threshold is determined to be the modulation frequency for the light emitted onto the tissue of the patient after the predefined interruption time period.

8. The method according to claim 3, wherein the step of emitting light onto the tissue of the patient is periodically interrupted.

9. The method according to claim 2, wherein the modulation frequency of the light emitted onto the tissue is consecutively changed by cycling through a predefined set of at least two frequency modes or frequency bands;

and

the modulation frequency for which the output of demodulating the collected light is maximized or exceeds a predefined threshold is determined to be the active modulation frequency for the light emitted onto the tissue of the patient.

10. The method according to claim 9, wherein during emitting light onto the tissue of the patient with a first modulation frequency, a second modulation frequency is selected from a predefined spectrum and vice versa.

11. The method according to claim 1, wherein the light emitted onto tissue of the patient comprises at least a first light and a second light, wherein the wavelength of the first light is different from the wavelength of the second light, and wherein the first light and the second light are multiplexed.

12. The method according to claim 11, wherein time division multiplexing, frequency multiplexing or/and code division multiplexing is applied.

13. The method according to claim 11, wherein the step of determining a modulation frequency or/and a modulation code for which the contribution of the ambient light is minimized or falls under a predefined threshold is done for only one of the first light and the second light, or is done for an average of the first light and the second light.

14. Device for monitoring a vital parameter of a patient by measuring attenuation of light emitted onto tissue of the patient, with

a light modulator adapted for modulating the light according to a modulation mode;

a light emitter adapted for emitting the modulated light onto the tissue of the patient;

a light detector adapted for light which is transmitted through the tissue or/and which is reflected from the tissue and unavoidably being adapted for collecting ambient light;

a light demodulator adapted for demodulating the collected light according to the modulation mode;

an interference analyzer adapted for analyzing the demodulated collected light with regard to the contribution of the ambient light; and

a processing unit adapted for determining a modulation mode for which the contribution of the ambient light is minimized or falls under a predefined threshold and for setting the modulation mode for modulating the light according to the determined modulation mode for which the contribution of the ambient light is minimized or falls under a predefined threshold.

15. The device according to claim 14, wherein at least two light sources for emitting light with two different wavelengths are provided.