Selection of filter parameters based on signal quality

Abstract

Methods and devices for reducing noise effects in a system for measuring a physiological parameter, including receiving an input signal, obtaining an assessment of the signal quality of the input signal, selecting coefficients for a digital filter using the assessment of signal quality; and filtering the input signal using the digital filter, without comparing the filter's output signal with the input signal.

1 . A method, comprising:
 receiving, at a processor, an input signal;   determining, with the processor, an assessment of signal quality for the input signal by determining a skew of a time derivative of the input signal or a variation in signal amplitude of the input signal;   selecting, with the processor, one or more coefficients for a digital filter using the assessment of signal quality without comparing an output of the digital filter with the input signal; and   filtering the input signal using the digital filter.   
     
     
         2 . The method of  claim 1 , wherein determining, with the processor, the assessment of signal quality comprises determining the skew of a time derivative of the input signal and determining the variation in signal amplitude of the input signal. 
     
     
         3 . The method of  claim 2 , wherein determining, with the processor, the assessment of signal quality comprises applying a first weight to the skew of the time derivative of the input signal and applying a second weight to the variation in signal amplitude of the input signal. 
     
     
         4 . The method of  claim 1 , wherein selecting, with the processor, the one or more coefficients for the digital filter comprises selecting one or more coefficients from a plurality of discrete preset values. 
     
     
         5 . The method of  claim 1 , wherein the digital filter comprises a linear digital filter. 
     
     
         6 . The method of  claim 1 , wherein the digital filter comprises a non-linear digital filter. 
     
     
         7 . The method of  claim 1 , wherein receiving, at the processor, the input signal comprises receiving the input signal from a pulse oximetry sensor, and wherein the input signal comprises a red waveform and an infrared waveform. 
     
     
         8 . The method of  claim 7 , wherein determining, with the processor, the assessment of signal quality for the input signal comprises determining a measure indicative of a degree of similarity between the red waveform and the infrared waveform. 
     
     
         9 . The method of  claim 7 , wherein determining, with the processor, an assessment of signal quality for the input signal comprises determining a measure indicative of a low light level. 
     
     
         10 . The method of  claim 7 , wherein determining, with the processor, an assessment of signal quality for the input signal comprises determining a measure indicative of an arterial pulse shape. 
     
     
         11 . A monitor, comprising:
 a processor configured to:
 receive an input signal from a medical sensor; 
 determine an assessment of signal quality for the input signal by determining a skew of a time derivative of the input signal or a variation in signal amplitude of the input signal; and 
 determine one or more digital filter coefficients using the assessment of signal quality; and 
   a digital filter configured to filter the input signal using the one or more digital filter coefficients, wherein the processor is configured to determine the one or more digital filter coefficients without comparing an output of the digital filter to the input signal.   
     
     
         12 . The monitor of  claim 11 , wherein the digital filter comprises a linear digital filter. 
     
     
         13 . The monitor of  claim 11 , wherein the processor is configured to determine the skew of a time derivative of the input signal and the variation in signal amplitude of the input signal to determine the assessment of signal quality for the input signal. 
     
     
         14 . The monitor of  claim 13 , wherein the processor is configured to apply a first weight to the skew of the time derivative of the input signal and apply a second weight to the variation in signal amplitude of the input signal to determine the assessment of signal quality for the input signal. 
     
     
         15 . The monitor of  claim 11 , wherein the medical sensor comprises a pulse oximetry sensor and the input signal comprises a red waveform and an infrared waveform. 
     
     
         16 . The monitor of  claim 15 , wherein the processor is configure to determine a measure indicative of a degree of similarity between the red waveform and the infrared waveform to determine the assessment of signal quality of the input signal. 
     
     
         17 . A system, comprising:
 a medical sensor configured to generate a physiological signal;   a processor configured to:
 receive the physiological signal from the medical sensor; 
 determine an assessment of signal quality for the physiological signal by determining a skew of a time derivative of the physiological signal or a variation in signal amplitude of the physiological signal; and 
 determine one or more digital filter coefficients using the assessment of signal quality; and 
   a digital filter configured to filter the physiological signal using the one or more digital filter coefficients;   wherein the processor is configured to determine the one or more digital filter coefficients without comparing an output of the digital filter to the physiological signal.   
     
     
         18 . The system of  claim 17 , wherein the medical sensor comprises a pulse oximetry sensor, and wherein the processor is configured to determine a measure indicative of an arterial pulse shape to determine the assessment of signal quality for the physiological signal. 
     
     
         19 . The system of  claim 18 , comprising a memory storing a plurality of digital filter coefficients, and wherein the processor is configured to select the one or more digital filter coefficients from the plurality of digital filter coefficients. 
     
     
         20 . The system of  claim 17 , wherein the processor is configured to determine the skew of the time derivative of the physiological signal and the variation in signal amplitude of the physiological signal and to apply a first weight to the skew of the time derivative of the physiological signal and a second weight to the variation in signal amplitude of the physiological signal to determine the assessment of signal quality of the physiological signal.