Signal processing apparatus
View Patent ↗The present invention involves method and apparatus for analyzing two measured signals that are modeled as containing primary and secondary portions. Coefficients relate the two signals according to a model defined in accordance with the present invention. In one embodiment, the present invention involves utilizing a transformation which evaluates a plurality of possible signal coefficients find appropriate coefficients. Alternatively, the present invention involves using statistical functions or Fourier transform and windowing techniques to determine the coefficients relating to two measured signals. Use of this invention is described in particular detail with respect to blood oximetry measurements.
1. A method for measuring saturation of a blood constituent in a patient comprising the steps of:
irradiating said patient with electromagnetic radiation of two discrete, different wavelengths;
sensing an intensity of said radiation for each of said wavelengths after it passes through a portion of said patient to produce first and second intensity signals including motion components; and
determining said saturation by mathematically manipulating said first and second intensity signals without subtracting said motion components and with the assumptions that
i) an amount of motion is the same at the same time for each of said intensity signals, and
ii) the motion components of said intensity signals are proportional to one another.
2. A method for measuring saturation of a blood constituent in a patient comprising the steps of:
irradiating said patient with electromagnetic radiation of two discrete, different wavelengths;
sensing an intensity of said radiation for each of said wavelengths after it passes through a portion of said patient to produce first and second intensity signals including motion components; and
determining said saturation by mathematically manipulating said first and second intensity signals without subtracting said motion components and with the assumptions that
i) an amount of motion is the same at the same time for each of said intensity signals, and
ii) the motion components of said intensity signals are proportional to one another,
wherein the step of determining said saturation further comprises
representing each of said intensity signals as a function of concentration, the wavelength corresponding to the intensity signal, and a time-variable motion term corresponding to motion noise, said motion terms being proportional to one another for each of said intensity signals;
taking the logarithm of each representation of said first and second intensity signals;
removing signal portions outside a known band of interest to create first and second filtered signals;
equating the first filtered signal of the first intensity signal to s+n, where n is the portion of the signal due to motion and s is the portion of the signal not due to motion;
equating the second filtered signal of the second intensity signal to r a s+r v n, where r a is a ratio indicative of saturation;
expressing said representations as a matrix;
using said matrix to determine r a by assuming s and n are uncorrelated; and
determining said saturation from r a .
3. The method of claim 2 , further comprising the step of displaying said saturation on a monitor.
4. A method for measuring the saturation of a blood constituent in a patient comprising the steps of:
irradiating said patient with electromagnetic radiation of two discrete, different wavelengths;
sensing an intensity of said radiation for each of said wavelengths after it passes through a portion of said patient to produce first and second intensity signals;
representing each of said intensity signals as a function of concentration, the wavelength corresponding to the intensity signal, and a time-variable motion term corresponding to motion noise, said motion terms being proportional to one another for each of said intensity signals;
taking the logarithm of each representation of said first and second intensity signals;
removing signal portions outside a known band of interest to create first and second filtered signals;
equating the first filtered signal of the first intensity signal to s+n, where n is the portion of the signal due to motion and s is the portion of the signal not due to motion;
equating the second filtered signal of the second intensity signal to r a s+r v n, where r a is a ratio indicative of saturation;
expressing said representations as a matrix;
using said matrix to determine r a by assuming s and n are uncorrelated; and
determining said saturation from r a .
5. An apparatus for measuring the saturation of a blood constituent in a patient comprising:
first and second emitters, said emitters emitting radiation of first and second different wavelengths;
a detector for sensing an intensity of said light, said detector being mounted relative to said first and second emitters so that said light is detected after it passes through a portion of said patient;
a controller for alternatively activating said emitters so that said detector detects the different wavelengths at different times to produce first and second intensity signals including motion components; and
control means for determining said saturation by mathematically manipulating said first and second intensity signals without subtracting said motion components and with the assumptions that
i) an amount of motion is the same at the same time for each of said intensity signals, and
ii) the motion components of said intensity signals are proportional to one another.
6. The apparatus of claim 5 , further comprising a display, coupled to said control means, for displaying said saturation.
7. A pulse oximeter for measuring the saturation of a blood constituent in a patient comprising:
first and second emitters, said emitters emitting radiation of first and second different wavelengths;
a detector for sensing an intensity of said light, said detector being mounted relative to said first and second emitters so that said light is detected after it passes through a portion of said patient;
a controller for alternatively activating said emitters so that said detector detects the different wavelengths at different times to produce first and second intensity signals including motion components; and
control means for determining said saturation by mathematically manipulating said first and second intensity signals with the assumptions that
i) an amount of motion is the same at the same time for each of said intensity signals, and
ii) the motion components of said intensity signals are proportional to one another,
wherein said control means further comprises
means for representing each of said intensity signals as a function of concentration, the wavelength corresponding to the intensity signal, and a time-variable motion term corresponding to motion noise, said motion term being correlated for each of said intensity signals;
means for taking the logarithm of each representation of said first and second intensity signals;
means for removing signal portions outside a known band of interest to create first and second filtered signals;
means for equating the first filtered signal of the first intensity signal to s+n, where n is the portion of the signal due to motion and s is the portion of the signal not due to motion;
means for equating the second filtered signal of the second intensity signal to r a s+r v n, where r is a ratio indicative of saturation;
means for expressing said representations as a matrix;
means for using said matrix to determine r a by assuming s and n are uncorrelated; and
means for determining said saturation from r a .