Motion compatible sensor for non-invasive optical blood analysis

• US 20050070773A1
• Filed: 11/16/2004
• Published: 03/31/2005
• Est. Priority Date: 10/10/1996
• Status: Active Grant

• Current Assignee: Nellcor Puritan Bennett LLC (Medtronic Plc)
• Original Assignee: Nellcor Puritan Bennett Incorporated (Medtronic Plc)
• Inventors: Mannheimer, Paul, Chin, Rodney, Flewelling, Ross
• Granted Patent: US 7,720,516 B2
• Time in Patent Office: Days
• US Class Current: 600/322
• CPC Class Codes: A61B 5/14552 Details of sensors specially adapted therefor
• CPC Class Codes: A61B 5/6826 Finger
• CPC Class Codes: A61B 5/6833 Adhesive patches
• CPC Class Codes: A61B 5/6838 Clamps or clips
• CPC Class Codes: A61B 5/7207 of noise induced by motion artifacts

Abstract

A non-invasive optical sensor which uses the motion signal to calculate the physiological characteristic being measured. For pulse oximetry, a least squares or a ratio-of-ratios technique can be applied to the motion signal itself. This is made possible by selecting a site on the patient where variations in motion produce signals of two wavelengths which are sufficiently correlated. In particular, it has been determined that a sensor placed on a nail, in particular a thumbnail, exhibits the characteristics of having the red and infrared signals correlated when used for pulse oximetry, and the resulting signals correlate to arterial oxygen saturation.

Claims

1. A photometric processing device for processing detector signals from a radiation detector in a patient sensor also having a radiation emitter, comprising:

a first processing unit configured to determine a blood parameter from a cardiac derived plethysmogram from said detector;

a second processing unit configured to determine said blood parameter from a motion artifact waveform from said detector; and

a control unit configured to utilize said first and second processing units responsive to a motion artifact content of said detector signals.

2. The photometric processing device of claim 1 further comprising a processor and a memory, wherein said first and second processing units and said control unit are first, second and third programs stored in said memory.

3. A photometric processing device for processing detector signals from a detector in a patient sensor having an emitter and a detector, comprising:

a stimulator configured to generate an artificial pulse in said patient, said artificial pulse being distinct from a cardiac derived arterial pulse; and

a processing unit configured to determine a physiological parameter of arterial blood from a signal from said detector representative of said artificial pulse.

4. The device of claim 3 wherein said physiological parameter is arterial oxygen saturation.

5. The device of claim 3 wherein said stimulator induces movement of an appendage of said patient.

6. The device of claim 3 wherein said stimulator comprises an inflatable bag and an attachment mechanism configured to attach said bag to one side of an appendage of said patient.

7. The device of claim 3 further comprising a bandpass filter coupled to receive a signal from said detector, said bandpass filter passing one of an amplitude, phase and frequency of said stimulator, wherein said distinction is one of an amplitude, phase and frequency.

8. The device of claim 7 wherein said frequency can be changed.

9. The device of claim 3 further comprising a frequency generator coupled to said stimulator.

10. The device of claim 9 wherein said frequency generator is configured to vary an output frequency.

11. A photometric processing device for processing detector signals from a detector in at least one patient sensor having an emitter and a detector, comprising:

a selector configured to select between a reflectance signal and a transmittance signal from said at least one sensor; and

a processing unit configured to determine a physiological parameter from a plethysmogram from said at least one sensor.

12. The device of claim 11 further comprising:

a first processing unit configured to determine a physiological parameter from a cardiac derived plethysmogram from said detector;

a second processing unit configured to determine said physiological parameter from a motion artifact waveform from said detector; and

a control unit configured to switch between said first and second processing units in accordance with a selection of said selector.

13. The device of claim 12 wherein said selector is responsive to a motion artifact content of a detector signal from said at least one sensor.

14. A method of measuring arterial oxygen saturation, comprising the steps of:

selecting a site on a patient wherein detected light signals from at least two wavelengths are sufficiently correlated in the presence of motion;

placing a pulse oximeter sensor on said site; and

measuring arterial oxygen saturation using said sensor.

15. The method of claim 14 wherein said light signals produce a closed Lissajous.

16. The method of claim 14 wherein said sufficiently correlated signals produce an arterial oxygen saturation that is accurate within 15 saturation points.

17. The method of claim 14 wherein said sufficiently correlated signals produce an arterial oxygen saturation that is accurate within 10 saturation points.

18. The method of claim 14 wherein said oxygen saturation is measured by analyzing at least two points on a waveform generated by motion of said patient.

19. A method for measuring a property of blood, comprising the steps of:

selecting a site on a patient wherein propagated light of at least two wavelengths will have sufficiently correlated waveforms in the presence of non-cardiac pulses;

placing a light emitter and light detector on said site; and

using signals derived from said light detector to measure said blood property.

20. The method of claim 19 wherein said signals include predominately motion-induced variations and said site is a nail on a digit.