Measurement of blood oxygen saturation
First Claim
1. A method for determining blood oxygen saturation comprising:
- compiling at least two blood absorption reference spectra, corresponding to two different levels of oxygenation, over a wavelength range;
directing light into the blood of a subject;
sensing a remitted light absorption spectrum from the blood;
compiling at least one minimum blood absorption reference spectrum and one maximum blood absorption reference spectrum corresponding to minimum and maximum blood oxygenation values, as well as at least one intermediate blood absorption reference spectrum; and
computing an oxygen saturation value as a function of the remitted light absorption spectrum relative to at least two of the blood absorption reference spectra.
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Accused Products
Abstract
Oxygenation of a subject'"'"'s blood is determined by sensing an absorption spectrum of light directed either invasively or non-invasively into the blood, and then calculating an oxygenation value by evaluating a cost function of the remitted spectrum relative to at least two pre-determined reference absorption spectra representing different, known levels of blood oxygenation. The source of light preferably uses stable, long-life, white LEDs, in which case white-balancing of the remitted spectrum can be accomplished by pre-determining and storing the spectrum of the LEDs, one time for all, and then adjusting the remitted spectrum accordingly to compensate for deviations of the LED spectrum from the constant ideal.
68 Citations
24 Claims
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1. A method for determining blood oxygen saturation comprising:
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compiling at least two blood absorption reference spectra, corresponding to two different levels of oxygenation, over a wavelength range; directing light into the blood of a subject; sensing a remitted light absorption spectrum from the blood; compiling at least one minimum blood absorption reference spectrum and one maximum blood absorption reference spectrum corresponding to minimum and maximum blood oxygenation values, as well as at least one intermediate blood absorption reference spectrum; and computing an oxygen saturation value as a function of the remitted light absorption spectrum relative to at least two of the blood absorption reference spectra. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11)
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12. A system for determining blood oxygenation saturation comprising:
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at least one processor; a storage device storing parameters numerically representing at least two blood absorption reference spectra, corresponding to two different levels of oxygenation, over a wavelength range wherein the storage device contains parameters numerically representing at least one minimum blood absorption reference spectrum and one maximum blood absorption reference spectrum corresponding to minimum and maximum blood oxygenation values, as well as at least one intermediate blood absorption reference spectrum; a light source generating a spectrum of light over at least the wavelength range; a light transmission arrangement directing the generated light from the light source into the blood of a subject; a light detection arrangement sensing a remitted light absorption spectrum from the blood; conditioning circuitry converting the detected remitted light into a numerically represented, measured remitted absorption spectrum; and a computation software module comprising processor-executable code for computing an oxygen saturation value as a function of the remitted light absorption spectrum relative to at least two of the blood absorption reference spectra. - View Dependent Claims (13, 14, 15, 16, 17, 18, 19, 20, 21, 22)
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23. A method for determining blood oxygen saturation comprising:
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compiling at least one minimum blood absorption reference spectrum and one maximum blood absorption reference spectrum corresponding to minimum and maximum blood oxygenation values, as well as at least one intermediate blood absorption reference spectrum, over a wavelength range each reference spectrum corresponding to a respective level of oxygenation; directing light into the blood of a subject; sensing a remitted light absorption spectrum from the blood; normalizing the blood absorption reference spectra and the remitted light absorption spectrum before computing the oxygen saturation value, the normalization including; DC-offsetting the spectra linearly between two isosbestic wavelengths that lie in the wavelength range; and scaling the DC-offsetted blood absorption reference spectra and the remitted light absorption spectrum by a function of the area under each respective DC-offsetted spectrum between the two isosbestic wavelengths; computing an oxygen saturation value as a function of the remitted light absorption spectrum relative to the blood absorption reference spectra, the computation including; computing an optimal value of a cost function that indicates closeness of correspondence between the remitted light absorption spectrum relative to the blood absorption reference spectra; and interpolation of the remitted light absorption spectrum relative to at least two of the blood absorption reference spectra; and computing the oxygen saturation value as a function of the remitted light absorption spectrum relative to at least two of the blood absorption reference spectra.
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24. A system for determining blood oxygenation saturation comprising:
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a least one processor; a storage device storing parameters numerically representing at least one minimum blood absorption reference spectrum and one maximum in blood absorption reference spectrum corresponding to minimum and maximum blood oxygenation values, as well as at least one intermediate blood absorption reference spectrum, each reference spectrum corresponding to respective, different levels of oxygenation, over a wavelength range; a light source generating a spectrum of light over at least the wavelength range; a light transmission arrangement directing the generated light from the light source into the blood of a subject; a light detection arrangement sensing a remitted light absorption spectrum from the blood; conditioning circuitry converting the detected remitted light into a numerically represented, measured remitted absorption spectrum; a computation software module including; a normalization sub-module comprising processor-executable code for normalizing the blood absorption reference spectra and the remitted light absorption spectrum before computing the oxygen saturation value by DC-offsetting the spectra linearly between two isosbestic wavelengths that lie in the wavelength range; and scaling the DC-offsetted blood absorption reference spectra and the remitted light absorption spectrum by a function of the area under each respective DC-offsetted spectrum between the two isosbestic wavelengths; and a fitting sub-module comprising processor-executable code for interpolating the remitted light absorption spectrum relative to at least two of the blood absorption reference spectra; the computation software module comprising processor-executable code for computing the oxygen saturation value as a function of the interpolation.
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Specification