Method for calibrating a system for recording and playing back ECG signals

• US 5,553,623 A
• Filed: 01/26/1995
• Issued: 09/10/1996
• Est. Priority Date: 03/12/1993
• Status: Expired due to Fees

• Current Assignee: Koninklijke Philips N.V.
• Original Assignee: Hewlett-Packard Company (HP Inc.)
• Inventors: Ochs, Dennis E.
• Primary Examiner(s): Kamm, William E.
• Application Number:
  US08/378,338
• Time in Patent Office: 593 Days
• Field of Search: 128/696, 128/710, 128/711
• US Class Current: 600/523
• CPC Class Codes: A61B 5/333 Recording apparatus specially adapted therefor
• CPC Class Codes: A61B 5/336 Magnetic recording apparatus
• CPC Class Codes: A61B 5/349 Detecting specific parameters of the electrocardiograph cycle
• CPC Class Codes: A61B 5/7203 for noise prevention, reduction or removal
• CPC Class Codes: A61B 5/7225 Details of analog processing, e.g. isolation amplifier, gain or sensitivity adjustment, filtering, baseline or drift compensation A61B5/30, A61B5/316 take precedence; transformers for specific applications H01F38/00; amplifiers H03F
• CPC Class Codes: A61B 5/7239 using differentiation including higher order derivatives
• CPC Class Codes: A61B 5/7257 using Fourier transforms

Abstract

An ECG recorder and playback unit which includes software-implemented digital signal processing filters which compensate for phase and magnitude distortion occurring when an ECG signal is recorded on a Holter recorder and played back. This permits "tuning" a recorder and playback unit which may be unrelated, as when made by different manufacturers. An impulse or step signal is recorded and played back to provide a system frequency response measurement. Coefficients for a digital correction filter are derived from the discrete Fourier transform of the impulse or step response and a desired system response. When recorded ECG data is played back, it is filtered on a substantially real-time basis with the digital correction filter to compensate for phase and magnitude distortion. Prior to recording, the high frequencies of the ECG signal are boosted to compensate for high frequency losses inherent in the recording and playing back of ECG signals. A calibration pulse and a system characterization pulse are derived by statistically selecting from a plurality of pulses and averaging the selected pulses in order to minimize the effects of noise and tape defects in the pulses. High frequency components of the ECG signal can be amplified prior to recording the signal. This results in decreased amplification, and therefore noise, when the recorded signals are played back. Cardiac pacer pulse detection is performed prior to the step of filtering the played back signal to optimize pulse detection.

Claims

1. A method for calibrating a system for recording and playing back ECG signals, said system having a gain capable of adjustment, said method comprising the steps of:

generating a plurality of calibration signals;

recording and playing back the calibration signals, thereby creating played-back calibration signals;

measuring the amplitude of the played-back signals, thereby creating measured amplitudes;

ranking the measured amplitudes from a highest measured amplitude to a lowest measured amplitude;

disregarding a predetermined number of both the highest and lowest measured amplitudes, wherein those measured amplitudes not disregarded are remaining amplitudes;

averaging the remaining amplitudes, thereby creating an average amplitude, and

using the average amplitude to adjust the gain of the system.

2. The method of claim 1, said system including a plurality of channels for simultaneously recording different ECG signals, wherein said generating, recording, measuring, ranking, disregarding, averaging and using steps are performed for each of the plurality of channels.

3. The method of claim 1, wherein said disregarding step disregards an equal number of highest measured amplitudes and lowest measured amplitudes.

4. The method of claim 3, wherein said disregarding step disregards 15% of the highest measured amplitudes and 15% of the lowest measured amplitudes.