Exponential Sampling Of Red And Infrared Signals

• US 20110029247A1
• Filed: 07/30/2009
• Published: 02/03/2011
• Est. Priority Date: 07/30/2009
• Status: Active Grant

• Current Assignee: Covidien LP (Medtronic Plc)
• Original Assignee: Nellcor Puritan Bennett LLC (Medtronic Plc)
• Inventors: Kalathil, Raghunath Mammulli
• Granted Patent: US 8,494,786 B2
• Time in Patent Office: Days
• US Class Current: 702/19
• CPC Class Codes: A61B 5/1455 using optical sensors, e.g. spectral photometrical oximeters
• CPC Class Codes: A61B 5/14551 for measuring blood gases

Abstract

Methods and systems are provided that include sampling a light intensity signal at different frequencies based on the waveform of the signal to produce a more accurate digitized signal. The light intensity signal is an analog signal proportional to the intensity of light received at a detector of a pulse oximetry system. In one embodiment, the signal may be sampled exponentially during pulse width periods, such that the end of the pulse width periods where the signal reaches a maximum amplitude may be sampled more frequently. The signal may also be exponentially sampled or oversampled during periods when the signal is expected to near maximum amplitude. Further, the signal may be sampled less frequently during low amplitude periods of the signal, and during dark periods, such that processing power may be conserved.

Claims

1. A method of processing a signal from a pulse oximetry sensor, comprising:

using a pulse oximeter, increasing a sampling rate of the signal in a substantially exponential manner during a sampling period.

2. The method, as set forth in claim 1, wherein the sampling rate is at or below a Nyquist rate during a first portion of the sampling period and at or above the Nyquist rate during the second portion of the sampling period.

3. The method, as set forth in claim 1, wherein increasing the sampling rate comprises oversampling the signal toward an end of the sampling period.

4. The method, as set forth in claim 1, wherein the signal comprises a red pulse width period, an infrared (IR) pulse width period, and/or a dark period.

5. The method, as set forth in claim 1, wherein increasing the sampling rate comprises oversampling the signal generally at a pulse rate.

6. A method of processing a signal from a pulse oximetry sensor, the method comprising:

using a pulse oximeter, increasing a sampling rate of the signal in a substantially linear manner during a sampling period.

7. The method, as set forth in claim 6, wherein the sampling rate is increased substantially in proportion to an amplitude of the signal.

8. The method, as set forth in claim 6, wherein the signal comprises a red pulse width period, an IR pulse width period, and a dark period.

9. The method, as set forth in claim 8, wherein the sampling period comprises the red pulse width period or the IR pulse width period.

10. A method of processing a signal from a pulse oximetry sensor, the method comprising:

using a pulse oximeter, sampling the signal at a relatively low sampling rate when the signal is in a relatively low period of interest and at a relatively high sampling rate when the signal is at a relatively high period of interest.

11. The method, as set forth in claim 10, wherein the relatively low rate is at or below a Nyquist frequency of the signal, and wherein the relatively high rate is at or above the Nyquist frequency of the signal.

12. The method, as set forth in claim 10, wherein sampling the signal comprises increasing the sampling rate substantially in proportion to an amplitude of the signal.

13. The method, as set forth in claim 10, wherein sampling the signal comprises increasing the sampling rate substantially linearly during a sampling period.

14. The method, as set forth in claim 10, wherein sampling the signal comprises increasing the sampling rate substantially exponentially during a sampling period.

15. The method, as set forth in claim 10, wherein sampling the signal comprises increasing the sampling rate substantially linearly generally at a pulse rate.

16. A pulse oximetry system, comprising:

an emitter configured to transmit light into tissue;

a detector configured to receive the light from the tissue and output a signal proportional to an intensity of the light from the tissue; and

a processor coupled to the detector, wherein the processor is configured to sample the signal at a relatively low rate when the signal has a relatively low amplitude and sample the signal at a relatively high rate when the signal has a relatively high amplitude.

17. The pulse oximetry system, as set forth in claim 16, wherein the relatively low rate is at or below a Nyquist frequency of the signal, and wherein the relatively high rate is at or above the Nyquist frequency of the signal.

18. The pulse oximetry system, as set forth in claim 16, wherein the signal comprises a red pulse width period, an IR pulse width period, and a dark period, and wherein the processor is configured to sample the signal substantially in proportion to an amplitude of the signal during the red pulse width period and the IR pulse width period, and configured to sample at a constant rate during the dark period.

19. The pulse oximetry system, as set forth in claim 16, wherein the processor is configured to sample the signal substantially linearly during a sampling period.

20. The pulse oximetry system, as set forth in claim 16, wherein the processor is configured to sample the signal substantially exponentially during a first sampling period.

21. The pulse oximetry system, as set forth in claim 20, wherein the processor is further configured to sample the signal substantially periodically during a second sampling period.