Simple two-electrode biosignal amplifier.

A simple, cost effective circuit for a two-electrode non-differential biopotential amplifier is proposed. It uses a 'virtual ground' transimpedance amplifier and a parallel RC network for input common mode current equalisation, while the signal input impedance preserves its high value. With this innovative interface circuit, a simple non-inverting amplifier fully emulates high CMRR differential. The amplifier equivalent CMRR (typical range from 70-100 dB) is equal to the open loop gain of the operational amplifier used in the transimpedance interface stage. The circuit has very simple structure and utilises a small number of popular components. The amplifier is intended for use in various two-electrode applications, such as Holter-type monitors, defibrillators, ECG monitors, biotelemetry devices etc.

Defibrillator-embedded rapid recovery electrocardiogram amplifier.

One of the most important performances of the defibrillator-embedded amplifier-monitor-recorder tract, connected to defibrillator electrodes, is its rapid recovery after the application of the shock pulse. Practically near-immediate restoration of the signal trace is mandatory for studies of post-shock effects on the myocardium. Automatic analysis of the electrocardiogram signal in public-access defibrillation, aiming for about 100% correct recognition of shockable and non-shockable rhythms, now requires fast amplifier settling, as the decision time should not exceed 10-20 s. Two circuits of post-shock amplifier transient suppressors were developed with non-linear feedback, resulting in second-order high-pass filtering, with gradual return to normally accepted first-order response. Simulation and testing in real conditions resulted in recovery periods in the range of 1-2 s for an amplifier tract of 1-30 Hz bandwidth, depending on the pulse waveform and electrode type.

Monitoring of fluctuating airway obstruction and episodes of coughing by thoracic electrical impedance.

The most prominent feature of bronchial asthma is the fluctuating airway obstruction of the affected subjects. Cough is also one of the major symptoms of asthma, but of other conditions as well. The continuous registration of airway obstruction and coughing in the working or open-air environment or at the homes of the potential sufferers may help establish a sometimes elusive diagnosis. To this purpose we developed a method using a measurement of the changes in the chest basal electrical impedance (Z0). A portable device for long-term recording of the Z0 signal was built using a microprocessor system. In order to assess both gradual Z0 changes, suggestive of altering airway patency and coughing episodes (characterized by abrupt changes), a continuous analogue-to-digital conversion (ADC) loop with a sampling frequency of 16 Hz was programmed. After completion of the recording, the memory of the portable instrument can be downloaded to a PC system for assessment and analysis. Appropriate averaging and filtering procedures have been worked out. This device may be further upgraded to give out a signal when Z0 starts to increase, so as to prevent a full-blown asthmatic crisis.