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Pulse oximeter with circuit leakage and ambient light compensation

  • US RE33,643 E
  • Filed: 04/10/1990
  • Issued: 07/23/1991
  • Est. Priority Date: 04/30/1987
  • Status: Expired due to Term
First Claim
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1. Apparatus for indicating the percentage of one or more constituents of arterial blood comprising, in combination:

  • (a) means for sequentially directing radiation of at least two discrete wavelengths along substantially the same path through a body part carrying arterial blood;

    (b) photosensing means positioned to intercept incident radiation including that passing through said body part and any ambient radiation for producing an electrical current proportional to the instantaneous intensity of the intercepted radiation;

    (c) logarithmic amplifier means coupled to said photosensing means for producing a time varying voltage solely proportional to the log of the component of said electrical current attributable to radiation of said at least two discrete wavelengths sequentially incident upon said photosensing means and excluding said ambient radiation;

    (d) pulse amplifier means coupled to the output of said logarithmic amplifier means for amplifying said time varying voltage irrespective of the differing direct current offsets upon which the time varying voltage may be superimposed; and

    (e) means .[.disposed in a single channel.]. .Iadd.disposed in one channel .Iaddend.responsive to the amplified time varying voltage for computing the percentage of said one or more constituents present in said arterial blood.

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