Apparatus for the automatic calibration of signals employed in oximetry

• US 5,259,381 A
• Filed: 07/10/1989
• Issued: 11/09/1993
• Est. Priority Date: 08/18/1986
• Status: Expired due to Term

• Current Assignee: NELLCOR PURITAN BENNETT
• Original Assignee: Physio-Control Incorporated (Stryker Corporation)
• Inventors: Smith, Robert E., Hunsaker, Scott W., Prosser, Stephen J., Gauglitz, Karl F., Cheung, Peter W., Wagner, Darrell O.
• Primary Examiner(s): Cohen, Lee S.
• Assistant Examiner(s): Nasser, Jr., Robert L.
• Application Number:
  US07/377,722
• Time in Patent Office: 1,583 Days
• Field of Search: 128/633, 128/634, 128/664-667, 330/59, 330/308, 250/214 A
• US Class Current: 600/323
• CPC Class Codes: A61B 2560/0252 using ambient temperature
• CPC Class Codes: A61B 2562/08 Sensors provided with means for identification, e.g. barcodes or memory chips
• CPC Class Codes: A61B 5/02427 Details of sensor
• CPC Class Codes: A61B 5/14552 Details of sensors specially adapted therefor
• CPC Class Codes: A61B 5/1495 Calibrating or testing of in-vivo probes
• CPC Class Codes: G01N 21/274 Calibration, base line adjustment, drift correction

Abstract

Under the present invention, a method and apparatus are provided for compensating for the effect temperature variations have on the wavelength of light emitted by the oximeter sensor light source (40, 42). In pulse oximetry, LEDs (40, 42) are typically employed to expose tissue to light at two different wavelengths. The light illuminating the tissue is received by a detector (38) where signals proportional to the intensity of light are produced. These signals are then processed by the oximeter circuitry to produce an indication of oxygen saturation. Because current oximetry techniques are dependent upon the wavelengths of light emitted by the LEDs (40, 42), the wavelengths must be known. Even when predetermined combinations of LEDs (40, 42) having relatively precise wavelengths are employed, variations in the wavelength of light emitted may result. Because the sensor (12) may be exposed to a significant range of temperatures while in use, the effect of temperature on the wavelengths may be significant. To compensate for this effect, a temperature sensor (50) is included in the sensor (12) to produce a signal indicative of sensor temperature. This signal is interpreted by the oximeter circuitry including, for example, a microcomputer (16), where the effect of temperature on wavelength is compensated for. In a preferred arrangement, this compensation takes the form of a computation of an alternative calibration curve from which the oxygen saturation is indicated, given a particular processing of signals from the detector (38).

Claims

1. An oximeter sensor comprising:

first and second light sources for illuminating tissue having arterial blood flowing therein, the light produced by each of said first and second sources being at a separate temperature dependent wavelength;

temperature indication means for producing an output indicative of the temperature of said first and second light sources;

light detection means, responsive to the illumination of said tissue, for producing signals that are proportional to the intensity of the light received at each of said temperature dependent wavelengths;

red optical filter means for filtering said light received by said light detection means;

and a sensor housing to which said first and second light sources, said temperature detection means, and said light detection means are connected.

2. An oximeter sensor comprising:

first and second light sources for illuminating tissue having arterial blood flowing therein, the light produced by each of said first and second sources being at a separate temperature dependent wavelength;

temperature indication means for producing an output indicative of the temperature of said first and second light sources;

light detection means, responsive to the illumination of said tissue, for producing signals that are proportional to the intensity of the light received at each of said temperature dependent wavelengths;

a reflective member positioned between said light detection means and said first and second light sources;

a sensor housing to which said first and second light sources, said temperature detection means, and said light detection means are connected, wherein said sensor housing comprises first and second elements, said first and second elements being attached to said first element and said light detection means attached to said second element, said first and second elements arranged to allow insertion of said tissue therebetween and to define a light path between said first and second light sources and said light detection means that includes said tissue, said light path including a first segment defined between said first and second light sources and said reflective member and a second segment defined between said reflective member and said light detection means, said first and second segments of said light path being at a predetermined angle to each other.

3. The sensor assembly of claim 2, wherein said first and second elements of said sensor housing are pivotally connected in a closably biased manner.