Pulse oximeter with circuit leakage and ambient light compensation
First Claim
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.
3 Assignments
0 Petitions
Accused Products
Abstract
An electronic apparatus for sensing the percentage of different blood constituents in arterial blood. Light of a plurality of separate wave lengths is sequentially made to pass through a portion of the body, either by direct transmission or scattering so that the pulsatile blood flow modulates the intensity of the light. A signal processing circuit functioning in accordance with the Lambert-Beer Law is used to determine the percentage of different blood constituents from the fluctuations component of the logarithm of the light absorption. The sampling of the separate wave lengths is time-multiplexed through a common channel, thus obviating the need for a separate channel of similar electronics for each constituent to be monitored. The signal processing circuitry is also effective to compensate for noise due to ambient light or other stray sources, thus improving the overall accuracy.
-
Citations
17 Claims
-
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. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11)
-
-
12. 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 responsive to the amplified time varying voltage for computing the percentage of said one or more constituents present in said arterial blood. .Iaddend. .Iadd.
-
-
13. 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 other extraneous current components attributable to ambient light and circuit current leakages; and (d) means responsive to the time varying voltage for computing the percentage of said one or more constituents present in said arterial blood. .Iaddend. .Iadd.
-
-
14. Apparatus for indicating the percentage of one or more constituents of arterial blood comprising, in combination:
-
(a) a plurality of light sources, each of a discrete wavelength for directing radiant energy pulses of a predetermined on-off duty cycle 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) operational amplifier means coupled to receive said electrical current as an input, said operational amplifier including first and second feedback paths, the first feedback path including a sample-and-hold circuit and an impedance element coupled in series, said sample-and-hold circuit tracking when said plurality of light sources are off and holding said electrical current when any of said plurality of light sources are on, said second feedback path including a gain determining element; and (d) means responsive to the output signal from said operational amplifier means for computing the percentage of said one or more constituents present in arterial blood. .Iaddend. .Iadd. - View Dependent Claims (15)
-
-
16. logarithmic response. .Iaddend. .Iadd.19. Apparatus for indicating the percentage of one or more constituents of arterial blood comprising, in combination:
-
(a) a plurality of light sources, each of a discrete wavelength for directing radiant energy pulses of a predetermined on-off duty cycle 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) operational amplifier means coupled to receive said electrical current as an input, said operational amplifier including first and second feedback paths, the first feedback path including a sample-and-hold circuit and an impedance element coupled in series, said sample-and-hold circuit tracking when said plurality of light sources are off and holding said electrical current when any of said plurality of light sources are on, said second feedback path including a gain determining element; (d) means for periodically routing said electrical current through said second feedback path only when said pair of light sources are on; and (e) responsive to the output signal from said operational amplifier means for computing the percentage of said one or more constituents present in
-
-
17. arterial blood. .Iaddend. .Iadd.20. The apparatus as in claim 19 wherein said gain determining element exhibits a non-linear response. .Iaddend. .Iadd.21. The apparatus as in claim 20 wherein said non-linear response is logarithmic. .Iaddend. .Iadd.22. The apparatus as in claim 19 wherein said impedance element in said first feedback path is a non-linear element. .Iaddend. .Iadd.23. The apparatus as in claim 22 wherein said non-linear element exhibits a logarithmic response. .Iaddend.
Specification