Blood parameter monitoring apparatus and methods
First Claim
1. Apparatus for monitoring a parameter of the blood within a body structure comprising:
- (a) illumination means for emitting light at at least one wavelength and directing the emitted light through said body structure;
(b) photodetector means for detecting light from said illumination means transmitted through said body structure and producing at least one photodetector signal representing the intensity of said detected light;
(c) carrier frequency means for varying the amplitude of the light emitted by said illumination means at at least one carrier frequency whereby said at least one photodetector signal will include at least one component at said at least one carrier frequency bearing information relating to the optical transmissivity of said body structure at said at least one wavelength;
(d) modification means for modifying said at least one photodetector signal by passing and attenuating components of said at least one photodetector signal dependent upon their respective frequencies so as to increase the ratio of said at least one carrier frequency component relative to other components and thereby provide at least one modifed signal;
(e) amplification means for amplifying each said modified signal to provide at least one amplified signal; and
(f) interpretation means for determining said parameter of the blood in said body structure from said at least one amplified signal.
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0 Petitions
Accused Products
Abstract
A pulse oximeter or plethysmographic device utilizes light varying in intensity at a predetermined carrier frequency. A passive resonant circuit having a resonant frequency substantially equal to the carrier frequency is connected between the photodetector and the first amplifier. The resonant circuit serves to suppress spurious DC and low frequency components such as those due to ambient light and ambient light flicker and also to suppress high frequency interference. Because ambient light signals are suppressed, there is no need for dark current correction or restoration. Suppression of ambient light and other interference upstream of the front end amplifier avoids saturation of the amplifier and permits use of a front end amplifier having high gain.
314 Citations
19 Claims
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1. Apparatus for monitoring a parameter of the blood within a body structure comprising:
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(a) illumination means for emitting light at at least one wavelength and directing the emitted light through said body structure; (b) photodetector means for detecting light from said illumination means transmitted through said body structure and producing at least one photodetector signal representing the intensity of said detected light; (c) carrier frequency means for varying the amplitude of the light emitted by said illumination means at at least one carrier frequency whereby said at least one photodetector signal will include at least one component at said at least one carrier frequency bearing information relating to the optical transmissivity of said body structure at said at least one wavelength; (d) modification means for modifying said at least one photodetector signal by passing and attenuating components of said at least one photodetector signal dependent upon their respective frequencies so as to increase the ratio of said at least one carrier frequency component relative to other components and thereby provide at least one modifed signal; (e) amplification means for amplifying each said modified signal to provide at least one amplified signal; and (f) interpretation means for determining said parameter of the blood in said body structure from said at least one amplified signal.
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2. Apparatus for monitoring a parameter of the blood within a body structure comprising:
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(a) illumination means for emitting light at at least one wavelength and directing the emitted light through said body structure; (b) photodetector means for detecting light from said illumination means transmitted through said body structure and producing at least one photodetector signal representing the intensity of said detected light; (c) carrier frequency means for varying the amplitude of the light emitted by said illumination means at at least one carrier frequency whereby said at least one photodetector signal will include at least one component at said at least one carrier frequency bearing information relating to the optical transmissivity of said body structure at said at least one wavelength; (d) modification means for modifying said at least one photodetector signal to increase the ratio of said at least one carrier frequency component relative to other components and thereby provide at least one modified signal; (e) amplification means for amplifying each said modified signal to provide at least one amplified signal; and (f) interpretation means for determining said parameter of the blood in said body structure from said at least one amplified signal, said modification means including at least one passive resonant circuit having a resonant frequency substantially equal to each said carrier frequency. - View Dependent Claims (3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16)
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17. A method of monitoring a parameter of the blood within a body structure comprising the steps of:
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(a) emitting light at at least one wavelength while varying the amplitude of the emitted light at at least one carrier frequency and directing the emitted light through the body sturcture; (b) detecting light transmitted through the body structure and producing at least one photodetector signal representative of the detected light and having at least one component at each said carrier frequency; (c) modifying said at least one photodetector signal by passing and attenuating components of said at least one photodetector signal depending upon their respective frequencies so as to increase the ratio of said at least one carrier frequency component to other components and thereby provide at least one modified signal; (d) amplifying said at least one modified signal to provide at least one amplified signal; and (e) determining said parameter from said at least one amplified signal. - View Dependent Claims (19)
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18. A method of monitoring a parameter of the blood within a body structure comprising the steps of:
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(a) emitting light at at least one wavelength while varying the amplitude of the emitted light at at least one carrier frequency and directing the emitted light through the body structure; (b) detecting light transmitted through the body structure and producing at least one photodetector signal representative of the detected light and having at least one component at each said carrier frequency; (c) modifying said at least one photodetector signal to increase the ratio of said at least one carrier frequency component to other components and thereby provide at least one modified signal; (d) amplifying said at least one modified signal to provide at least one amplified signal; and (e) determining said parameter from said at least one amplified signal, said amplifying step including the step of passing said photodetector signal to an input node of an amplifier, and said attenuating step includes the step of maintaining a passive circuit resonant at said at least one carrier frequency in parallel with said amplifier input node.
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Specification