M. J. Burke

A micropower dry-electrode ECG preamplifier

This paper describes the development of a very low-power preamplifier intended for use in pasteless-electrode recording of the human electrocardiogram. The expected input signal range is 100 /spl mu/V-10 mV from a lead-II electrode configuration. The amplifier provides a gain of 43 dB in a 3-dB bandwidth of 0.05 Hz-2 kHz with a defined high input impedance of 75 M/spl Omega/. It uses a driven common electrode to enhance rejection of common-mode interfering signals, including low-frequency motion artifact, achieving a common-mode rejection ratio (CMRR) of better than 80 dB over its entire bandwidth. The gain and phase characteristics meet the recommendations of the American Heart Association, ensuring low distortion of the output ECG signal and making it suitable for clinical monitoring. The amplifier has a power consumption of 30 /spl mu/W operating from a 3.3-V battery and is intended for use in small, lightweight, portable electrocardiographic equipment and heart-rate monitoring instrumentation.

Sphygmomanometers in hospital and family practice: problems and recommendations.

The accuracy and working condition of 210 sphygmomanometers were tested: 100 (50 and mercury and 50 aneroid) models were used in family practices and 100 mercury models in hospitals. Faults in the inflation-deflation system were common and caused mainly by dirt or wear in the control valves. Leakage occurred in 48% of the hospital and 33% of the family practice sphygmomanometers. In the mercury models the mercury or air vents were often in an unsatisfactory condition or the calibrated glass tube dirty. The accuracy of the gauges was examined at 90 and 150 mm Hg: fewer than 2% of the mercury sphygmomanometers but 30% of the aneroid models had errors greater than +/- 4 mm Hg at either pressure. Over half of the cuffs examined had bladders widths less than the recommended size, and 94% had bladders shorter than the length recommended for use on normal adults. Mercury sphygmomanometers should be bought in preference to aneroid models as they are more accurate, less expensive in the long term, and can be maintained by the owner; they should be checked every six to 12 months depending on usage. Replacement parts should be kept readily available.

Time Based Measurement of the Impedance of the Skin-Electrode Interface for Dry Electrode ECG Recording

This paper reports the measurement of the properties of dry or pasteless conductive electrodes to be used for long-term recording of the human electrocardiogram (ECG). Knowledge of these properties is essential for the correct design of the input stage of associated recording amplifiers. Measurements were made on three commercially available conductive carbon based electrodes at pressures of 5mmHg and 20mmHg, located on the lower abdomen of the body on three subjects having different skin types. Parameter values were fitted to a two-time-constant based model of the electrode using data measured over a period of 10s. Values of resistance, ranging from 40kOmega to 1590kOmega and of capacitance ranging from 0.05muF to 38muF were obtained for the components, while the values of the time-constants varied from 0.07s to 3.9s.

Wavelet based analysis and characterization of the ECG signal

This paper reports the use of a wavelet analysis technique based on the Mexican Hat wavelet to identify the onset and termination points and the duration of the principal constituent components of the human electrocardiogram (ECG). ECG recordings were obtained from 21 healthy subjects aged between 13 and 65 years, over a wide range of heart rates extending from 46 to 184 beats min−1. A wavelet transform method was then used to locate precisely the positions of the onset, termination and the durations of individual components in the ECG. Component times were then classified according to the heart rate associated with the cardiac cycle to which the component belonged. Second order equations of the form were fitted to the data obtained for each component to characterize its timing variation.

An accurate programmable ECG simulator.

This article reports the design and development of an ECG simulator intended for use in the testing, calibration and maintenance of electrocardiographic equipment. It generates a lead II signal having a profile that varies with heart rate in a manner which reflects the true in vivo variation. Facilities are provided for user adjustment of heart rate, signal amplitude, QRS complex up-slope, and the relative amplitudes of the P-wave and T-wave. The heart rate can be set within the range 30 - 200 beats min-1 in steps of 1 beat min-1. The amplitude of the QRS complex can be adjusted from 0.1 - 20 mV in 0.1 mV steps, while its up-slope can be set between 10 and 50 ms with a 1 ms resolution. The amplitude of the P-wave can be varied from 5 - 40% and that of the T-wave from 10 - 80% of the amplitude of the QRS complex with a 1% resolution.

Amplifier input impedance in dry electrode ECG recording

This paper presents a novel approach for designing the front-end of instrumentation amplifiers for use in dry electrode recording of the human electrocardiogram (ECG). The method relies on information provided by the characterization of the skin-electrode interface and the analysis of low frequency ECG criteria defined by international standards. Marginal measurements of capacitive elements of the skin-electrode interface as small as 0.01 µF, suggest values of input impedance in the order of 1.3 GΩ. However, results in 99% of the data analyzed indicate that a recording amplifier providing an input impedance of 500 MΩ should ensure clear signal sensing without distortion.

The time relationships of the constituent components of the human electrocardiogram

This paper reports the results of an examination of the timing relationships of the principal constituent components of the human electrocardiogram (ECG). ECG recordings were obtained from 21 healthy subjects, 10 male and 11 female aged between 13 and 65 years, over a wide range of heart rates extending from 46 to 184 beats per minute (bpm). A wavelet transform method based on the Mexican Hat wavelet was then used to precisely locate the positions of the onset, peak, termination and the duration of individual components in the ECG. Component times were then classified according to the heart rate associated with the cardiac cycle to which the component belonged. Second-order equations in the square root of the cardiac cycle time, T R-R of the form AT R-R 1/2 +BT R-R +C were fitted to the data obtained for each component to characterize its timing variation. These equations may be used to synthesize an ECG signal having a profile that varies with heart rate in a manner which reflects the in vivo variation.

The accuracy and reliability of commercial heart rate monitors.

In recent years increasing emphasis has been placed on the benefits of exercise to normal healthy adults as well as to those recovering from heart attacks and other illnesses. As an aid to exercise training many portable heart-rate monitors have been placed on the market but little appears to have been done to assess the performance of these machines. The authors have examined the performance of four such monitors both under bench-test and practical exercising conditions. When tested on the bench using electronic equipment, the machines rarely exhibited errors exceeding 2-3 bpm over a measurement range of 30-240 bpm. However, when tested with subjects walking or jogging at low speeds on a treadmill, typically 20-70% of the readings given by the machines had errors of greater than 20 bpm. In some cases over 50% of readings had errors exceeding 50 bpm.

A time domain based classifier for ECG pattern recognition

Pattern recognition, and in particular dynamic time warping has been applied to the ECG for many different purposes over the last decade. Significant research on creating adaptive, feature based, and more complex forms of the algorithm in order to increase its ability to classify an ECG signal accurately has been performed. Despite this increase in complexity and in the number of variations of the dynamic time warping algorithm there has been less focus on actually using the results of dynamic time warping to relate the reference and test signals to each other as accurately as possible. The majority of dynamic time warping algorithms published in the literature, even the most complex of them, classify the most accurate match to a reference signal based only on resulting Euclidean distance or slope difference between samples of the known reference and unknown query signal. This article demonstrates how a combination of measurements including heart-rate, amplitude and required warping time alignment can be used to reduce the resulting error in the classification of a query signal after the query and reference signals have been warped together. Its benefits are verified with significant testing.

A precision ECG signal generator providing full Lead II QRS amplitude variability and an accurate timing profile

This paper reports the design and development of a precision ECG signal generator intended for use in test and calibration of electrocardiographic equipment, ECG signal processing systems and as a cardiac teaching tool. It generates a Lead II signal which maintains the timing and profile characteristics of a Lead II electrocardiograph signal across a range of heart rates between 45 and 185 bpm in 1 bpm steps. The QRS amplitude can be adjusted in 1 µV increments from 100 µV to 10 mV. The up-slope of the QRS can be set between 15 ms and 45 ms with 1 ms resolution. The P and T wave amplitudes can be adjusted as a 1–100% scaling of the QRS complex amplitude with a 1% resolution. A color LCD with touch screen capability provides the user with facilities for inputting parameters, viewing the output wave parameters and a graphical representation of the resulting output waveform. The signal generator outputs a precision differential signal via a digital to analogue stage which has been designed using low noise techniques to produce accurate signals at the lower end of the QRS amplitude range.