Signal component processor
View Patent ↗A signal processor generates basis functions and identifies at least one basis function component of a sensor signal in order to calculate a physiological measurement. The signal processor is advantageously applied to pulse oximetry so as to directly calculate oxygen saturation and so as to calculate a robust oxygen saturation measurement. In particular, a signal component transform may be calculated within a window around a derived pulse rate estimate. A signal component transform may also utilize sinusoidal basis functions, and an optimization of a signal component transform may occur at a particular frequency or a set of frequencies. A sinusoidal waveform or waveforms at that frequency or set of frequencies is generated to select associated red and infrared components of the sensor signal, and an oxygen saturation is calculated from a magnitude ratio of these components.
1. A pulse oximeter system comprising:
an input capable of accepting a physiological signal; and
a component processor capable of communicating with said input and comprising:
a first calculator capable of determining a basis function index from said signal; and
a second calculator capable of generating a basis function waveform according to said index, deriving a component from said sensor signal and said waveform, and generating a physiological measurement responsive to said component, wherein second calculator derives said component using at least the inner product of said sensor signal and said waveform.
2. A pulse oximeter system comprising:
an input capable of accepting a physiological signal; and
a component processor capable of communicating with said input and comprising:
a first calculator capable of determining a basis function index from said signal; and
a second calculator capable of generating a basis function waveform according to said index, deriving a component from said sensor signal and said waveform, and generating a physiological measurement responsive to said component, wherein said first calculator determines a basis function frequency as said basis function index, and said second calculator generates a sinusoid at said frequency as said basis function waveform.
3. The pulse oximeter system according to claim 2 , wherein said first calculator derives a pulse rate estimate from said signal selects said frequency from a window including said pulse rate estimate.
4. The pulse oximeter system according to claim 2 , wherein said second calculator generates an oxygen saturation value responsive to a magnitude of said component as said physiological measurement.
5. A signal processing method comprising the steps of:
receiving a sensor signal;
calculating an estimated pulse rate;
determining an optimization of said sensor signal proximate said estimated pulse rate;
defining a frequency corresponding to said optimization; and
outputting a physiological measurement responsive to a component of said sensor signal at said frequency, and
wherein said outputting step comprises the substeps of:
inputting a red (RD) portion and an infrared (IR) portion of said sensor signal;
deriving a RD component of said RD portion and an IR component of said IR portion corresponding to said frequency; and
computing an oxygen saturation based upon a magnitude ratio of said RD component and said IR component; and
wherein said deriving step comprises the substeps of:
generating a sinusoidal waveform at said frequency; and
selecting said RD component and said IR component utilizing said waveform.
6. The signal processing method according to claim 5 , wherein said selecting step comprises the substep of calculating the inner product between said waveform and said RD portion and the inner product between said waveform and said IR portion.
7. The signal processing method according to claim 6 , wherein said selecting step comprises the substeps of:
canceling said waveform from said RD portion and said IR portion, leaving a RD remainder and an IR remainder; and
subtracting said RD remainder from said RD portion and said IR remainder from said IR portion.
8. A signal processor comprising:
a first calculator means for deriving an optimization frequency from a pulse rate estimate and a sensor signal; and
a second calculator means for deriving a physiological measurement responsive to a sensor signal component at said frequency,
wherein said first calculator means comprises:
a signal component transform means for determining a plurality of signal values corresponding to a plurality of selected frequencies within a window including said pulse rate estimate; and
a detection means for determining a particular one of said selected frequencies corresponding to an optimization of said sensor signal; and
wherein said second calculator means comprises:
a waveform means for generating a sinusoidal signal at said frequency;
a frequency selection means for determining a component of said sensor signal from said sinusoidal signal; and
a calculator means for deriving a ratio responsive to said component.