For suppressing cardiovascular artifact present in a respiration signal, a cardiovascular artifact filter suppresses artifacts in response to an output signal generated by a cardiotachometer. The output signal is proportional to the fundamental frequency of the cardiovascular artifact. Recurrence of respiration is determined by coupling the filter to a threshold detector. A minimum threshold level proportional to the maximum amplitude of the artifact is supplied to the detector for minimizing the false indication of respiration recurrence due to presence of an artifact in the respiration signal.
For suppressing cardiovascular artifact from a respiration signal derived from a patient's transthoracic impedance, an adaptive filtering device determines the patient's heart rate, converts the respiration signal from an analog to digital representation at a rate proportional to the heart rate, and then filters the digital respiration signal such that that portion of the respiration signal having a frequency content at or above the heart rate is most greatly attenuated.
A diagnostic medical imaging device including a signal processor that includes an adaptive filter noise canceler that is used to reduce the additive electrical noise on low power bio-potential signals caused by a patient's respiration. A noise reference signal associated with the patient's respiration is adaptively filtered with only minimal time delay and subtracted from a noisy bio-potential signal that is acquired from the patient. The resultant signal is a clean bio-potential signal that may be used for, among other things, triggering an MRI scan. The noise reference signal is received by an adaptive filter having adjustable filter coefficients. The filter coefficients are adjusted using the clean bio-potential signal that acts an error signal.
A filter system for removing small amplitude, high frequency signals such as muscle artifact signals from an ECG signal is provided. The filter system includes a low pass filter with variable cutoff frequencies, an electronic delay and a system for detecting the R wave in the ECG signal and determining the variable cutoff frequency in response to the detection of the R wave. A digitized input ECG signal is simultaneously presented to the electronic delay and the system for detecting the R wave. During the portion of the ECG signal exclusive of the QRS complex, the filter is operated at a low cutoff frequency to filter the muscle artifact signals for a maximum smoothing effect. At a time slightly prior to the on set of the QRS complex, the cutoff frequency is rapidly incrementally increased to a higher cutoff frequency to pass the QRS complex with a minimum reduction of amplitude of the QRS signal. At the end of the QRS signal, the cutoff frequency of the filter is rapidly incrementally returned to the low cutoff frequency.
