Method Of Analyzing Photon Density Waves In A Medical Monitor

• US 20110077485A1
• Filed: 09/30/2009
• Published: 03/31/2011
• Est. Priority Date: 09/30/2009
• Status: Active Grant

• Current Assignee: Covidien LP (Medtronic Plc)
• Original Assignee: Nellcor Puritan Bennett LLC (Medtronic Plc)
• Inventors: McKenna, Edward M., Baker, Clark R. JR.
• Granted Patent: US 8,401,608 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 5/0261 using optical means, e.g. infrared light
• CPC Class Codes: A61B 5/0295 using plethysmography, i.e. measuring the variations in the volume of a body part as modified by the circulation of blood therethrough, e.g. impedance plethysmography
• CPC Class Codes: A61B 5/14551 for measuring blood gases
• CPC Class Codes: A61B 5/14552 Details of sensors specially adapted therefor
• CPC Class Codes: A61B 5/7203 for noise prevention, reduction or removal
• 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 5/7239 using differentiation including higher order derivatives
• CPC Class Codes: G01N 21/3151 using two sources of radiation of different wavelengths G01N21/33 - G01N21/39 take precedence

Abstract

A monitoring system that may include an emission feature capable of emitting light into tissue, a modulator capable of modulating the emitter at a modulation frequency generally in a range of about 50 MHz to 3.0 GHz to generate resolvable photon density waves, a detection feature capable of detecting photons of the photon density waves after passage through the tissue and capable of providing a distribution of detected photons over a time period for the photon density waves, and a processor capable of calculating a skewness of the distribution and making determinations relating to a value of a physiologic parameter of the tissue based at least in part on the skewness of the distribution.

Claims

1. A monitoring system, comprising:

an emission feature capable of emitting light into tissue;

a modulator capable of modulating the emitter at a modulation frequency generally in a range of about 50 MHz to 3.0 GHz to generate a generally resolvable photon density waves;

a detection feature capable of detecting photons of the photon density waves after passage through the tissue and capable of providing a distribution of detected photons over a time period for the photon density waves; and

a processor capable of calculating a skewness of the distribution and making determinations relating to a value of a physiologic parameter of the tissue based at least in part on the skewness of the distribution.

2. The system of claim 1, comprising a memory storing empirical data, wherein the processor is capable of analyzing the skewness by comparing the skewness to the empirical data stored in the memory.

3. The system of claim 1, wherein the empirical data comprises skewness values for various vascular disease conditions of tissue.

4. The system of claim 1, wherein the detection feature comprises a signal processing device capable of providing the distribution by determining a derivative of a detected waveform of the photon density waves.

5. The system of claim 4, comprising a noise-reduction feature capable of enhancing a single-to-noise level of the distribution via an ensemble averaging procedure.

6. The system of claim 5, wherein the noise-reduction feature is capable of triggering the ensemble averaging procedure based at least in part on a modulation waveform produced by the modulator to modulate the emitter.

7. The system of claim 1, wherein the emission feature comprises a pair of laser diodes each capable of emitting a different wavelength of light.

8. The system of claim 1, wherein the processor is capable of determining a blood oxygen saturation level based at least in part on an amplitude of the distribution.

9. The system of claim 1, wherein the detection feature comprises a photodetector disposed within a monitor and fiber optic cable coupled to a sensor body.

10. The system of claim 1, wherein the processor is capable of calculating an estimated number of scattering particles in the tissue based at least in part on detected phase shifts.

11. The system of claim 1, comprising a plurality of emitters, wherein the modulator is capable of modulating light from the plurality of emitters to generally sweep the tissue with a plurality of modulation frequencies.

12. A method of analyzing tissue, comprising:

modulating light from an emitter of a patient monitoring device at a modulation frequency in a range of about 50 MHz to 3.0 GHz to generate photon density waves;

transmitting the photon density waves into a medium;

detecting the photon density waves after passing through at least a portion of the medium;

providing a data distribution of detected photons over a time period for the photon density waves;

calculating a skewness of the data distribution;

providing a value of a physiologic parameter of the tissue based at least in part on the skewness of the data distribution.

13. The method of claim 12, comprising analyzing the skewness by comparing the skewness to previously acquired empirical data that is indicative of known tissue conditions.

14. The method of claim 12, wherein providing the data distribution comprises determining a derivative of a detected waveform of the photon density waves.

15. The method of claim 12, comprising enhancing a signal-to-noise level of the data distribution via an ensemble averaging procedure.

16. The system of claim 15, comprising triggering the ensemble averaging procedure based at least in part on the modulation frequency.

17. A pulse oximeter, comprising:

a modulation feature capable of modulating an emitter at modulation frequencies in a range of about 50 MHz to 3.0 GHz to produce photon density waves of red and infrared light;

a detector capable of detecting the photon density waves after the photon density waves have passed through tissue and using data acquired from detection of the photon density waves to output a photon density wave signal that is indicative of a number of photons detected over a time period;

analysis circuitry capable of calculating a skewness of the photon density wave signal that correlates to scattering of the photons in the tissue, wherein the analysis circuitry is capable of identifying characteristics of the tissue based at least in part on a comparison of operational aspects of the modulation feature and the skewness of the photon density wave signal.

18. The pulse oximeter of claim 17, wherein the analysis circuitry comprises a processor capable of comparing the skewness with established values to facilitate identification of certain characteristics of the tissue.

19. The pulse oximeter of claim 17, comprising a noise-reduction feature capable of enhancing a signal-to-noise level of the distribution via an ensemble averaging procedure.

20. The pulse oximeter of claim 17, wherein the emitter comprises a non-sinusoidal emitter.