Siemens Elema Ab

Siemens Aktiengesellschaft

Peter Karlsson

Thomas Ohlsson

Lena Lundstrom

A device for filtering ECG signals has an A/D converter and a filter unit connected to the converter's output. The filter unit includes a filter, or a combination of filters with a non-linear phase response such that signals with frequencies in the passband of the filter, or the combination of filters, are delayed more than signals with frequencies in the transition band between the passband and the suppressed frequency band of the filter, or the combination of filters. A method for producing an FIR filter, with a phase response opposite to the phase response of a filter for filtering out DC components, or an IIR filter, suitable for use in the above-described device, is also disclosed in which the impulse response from the filter for filtering out DC components and low-frequency components or the IIR filter is reversed in time and sampled. The sampled values are then used for determining coefficients for the FIR filter.

Device for filtering ECG signals

In a method for correcting for non-physiological variations in ECG signals, signals recorded during a heartbeat, or a characteristic part of a heartbeat, are conditioned and digitized. Signal samples are stored in the form of an m.times.p matrix, where m is the number of samples and p is the number of leads used from measuring electrodes applied to the patient. The difference between this measuring matrix and a reference matrix is minimized by performing one or more of the operations translation, time synchronization, rotation and scaling of the measuring matrix. An apparatus for correcting for non-physiological variations in ECG signals includes a stage for conditioning signals, picked up by measuring electrodes applied to the patient, an A/D converter for digitizing the signals and a calculation unit. The calculation unit includes a storage unit for storing signal samples in the form of a m.times.p matrix, where m is the number of samples and p is the number of leads used from measuring electrodes applied to the patient, and for storing a reference matrix. The calculation unit is arranged to minimize the difference between the measuring matrix, formed from signal samples, and the reference matrix by one or more of the operations of translation, time synchronization, rotation and scaling of the measuring matrix.

Method and apparatus for correcting non-physiological variations in ECG

A device for eliminating ringing in filtered ECG signals includes an analog-to-digital for converting the ECG input signals into a series of digital values, and a filter unit connected to the output of the analog-to digital converter. The filter unit includes a recursive IIR-filter and a subsequent allpass filter with a phase shift which is equal to twice the phase shift of the IIR filter. The allpass filtering is performed time-reversed with respect to the IIR filtering. In a method for producing an allpass filter, for use in the above device, having a phase shift which is equal to twice the phase shift of an IIR filter, the IIR filter having zero points situated on the unity circle in the Z-plane, the zero points of the IIR filter are replaced by new zero points obtained by reflecting the poles of the filter in the unity circle in the Z-plane.

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Stockholm, Sweden

Peter Karlsson