Feedback-controlled method and apparatus for processing signals used in oximetry
First Claim
1. A method of processing information signals that contain information about the oxygen saturation of arterial blood flowing in tissue, comprising the steps of:
- subtracting from said information signal a controlled portion of said information signal, the magnitude of said controlled portion being determined by a subtraction control signal;
producing a subtraction output that is substantially equal to the portion of said information signal remaining after said controlled portion is subtracted therefrom; and
producing said subtraction control signal, the magnitude of said subtraction control signal produced being a function of said subtraction output and indicating any adjustment to be made in said controlled portion subtracted from said information signal.
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Accused Products
Abstract
A feedback control system is disclosed for use in processing signals employed in pulse transmittance oximetry. The signals are produced in response to light transmitted through, for example, a finger at two different wavelengths. Each signal includes a slowly varying baseline component representing the relatively fixed attenuation of light produced by bone, tissue, skin, and hair. The signals also include pulsatile components representing the attenuation produced by the changing blood volume and oxygen saturation within the finger. The signals are processed by the feedback control system before being converted by an analog-to-digital (A/D) converter (72) for subsequent analysis by a microcomputer (16). The feedback control system includes a controllable offset subtractor (66), a programmable gain amplifier (68), controllable drivers (44) for the light sources (40,42), and the microcomputer (16). The microcomputer receives signals from the offset subtractor (66), gain amplifier (68), drivers (44) and A/D converter (72) to produce signals that control the function of the subtractor (66) and drivers (44) in the following manner. Normally, the drivers (44) are maintained within a predetermined current range. In the event the microcomputer (16) senses an output from the converter (72) that is not within a predetermined range, the drive signal is adjusted to produce an acceptable signal. The magnitude of the offset removed by the subtractor (66), as controlled by the microcomputer (16), is maintained at a constant level when the converter (72) output is within a first predetermined range and is a predetermined function of the converter (72) output when that output falls within a second predetermined range.
205 Citations
27 Claims
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1. A method of processing information signals that contain information about the oxygen saturation of arterial blood flowing in tissue, comprising the steps of:
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subtracting from said information signal a controlled portion of said information signal, the magnitude of said controlled portion being determined by a subtraction control signal; producing a subtraction output that is substantially equal to the portion of said information signal remaining after said controlled portion is subtracted therefrom; and producing said subtraction control signal, the magnitude of said subtraction control signal produced being a function of said subtraction output and indicating any adjustment to be made in said controlled portion subtracted from said information signal. - View Dependent Claims (2, 3)
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4. An apparatus for receiving and processing signals, produced by a sensor, that contain information about the oxygen saturation of arterial blood flowing in tissue, said apparatus comprising:
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offset subtraction means for subtracting from said sensor signal a controlled portion of said signal, said offset subtraction means having an output that is substantially equal to the portion of said sensor signal remaining after said controlled portion is subtracted therefrom; control means for receiving said output of said offset subtraction means and providing a subtraction control signal, which is dependent on said output, to said subtraction means to control the magnitude of said portion of said sensor signal; and analyzing means for receiving said output of said subtraction means and producing an indication of the oxygen saturation of said arterial blood flowing in said tissue. - View Dependent Claims (5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20)
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21. An oximeter, comprising:
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a controllable-intensity light source, responsive to a source control signal, for illuminating tissue having arterial blood flowing therein, the intensity of light with which said tissue is illuminated being determined by said source control signal; detection means, responsive to the illumination of said tissue, for producing a signal containing information about the oxygen saturation of said arterial blood; offset subtraction means, responsive to a subtraction control signal, for subtracting from said detection means signal a controlled portion of said signal, the magnitude of said controlled portion being determined by said subtraction control signal, said subtraction means having an output that is substantially equal to the portion of said detection means signal remaining after said controlled portion is subtracted therefrom; a controllable-gain amplifier, responsive to a gain control signal, for amplifying said subtraction means output by a controlled gain, the magnitude of said gain being determined by said gain control signal, said amplifier having an output that is substantially equal to the product of said subtraction means output and said gain; control means for producing said source control signal, said subtraction control signal, and said gain control signal, said source and subtraction control signals being predetermined functions of said amplifier output; and analyzing means for receiving said amplifier output and producing an indication of the oxygen saturation of said arterial blood flowing in said tissue. - View Dependent Claims (22, 23, 24, 25, 26, 27)
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Specification