Text 13. Electrodes

Floating Electrode

Even the best electrodes for picking up potentials from the skin for ECG, EEG and EMG cause artefacts when there is movement. The movement changes the quality of contact between the electrode and skin, thus affecting the electrode potential and resistance.

This problem can be reduced by mounting the electrode a short distance from the skin on a plastic washer, and filling the recess with electrode jelly. This is called a floating electrode, or a fluid column electrode.

Suction Electrode

In electrocardiography, the precordial (chest) electrode may sometimes consist of a short metal cylinder which makes contact with the skin at its base, which is smeared with conductive electrode jelly. The upper end of the tube is connected to a rubber bulb which is squeezed and then released as the tube makes contact with the skin. It adheres to the skin by suction while the recording is made and then it can be moved to another site. The contact impedance is higher than for the larger surface area electrodes used for the limb leads.

Microelectrode

In studying the electrophysiology of cells it is often necessary to measure the potential difference across the cell membrane. To do this the electrode must measure from within the cell. Very small electrodes can be made with tip sizes ranging from 0.05 to 10 [u]m. They may be formed from solid metal needles, metal contained within or on the surface of glass needles, or from a glass micropipette having the lumen filled with electrolytic solution. The electrode must be used with a special micromanipulator to enable the tip to be moved with precision through the cell wall.

TEXT 14. Super-High Resolution Electrocardiograph SHR-ECG

EDR's 8-channel processor is able to detect the faint signals from the body's surface at least down to 6x10⁷ Vp-p. nearly 100% percent of the faint heart beats are measured. 

EDR has developed a more advanced 8-channel Super-Sensitive Neural-Cell Processor (SSNCP). The long-term objective is to exploit the processor's super-high sensitivity for manufacturing a new breed of diagnostic equipment capable of recording extremely low-level signals from the body surface on a beat-by-beat basis.

There are quite a few additional applications for detection of various small signals that have been developed now that the technology is recognized and financial backing is available. A super-sensitive device on the market provides needed support to researchers worldwide in their desire to test non-invasively or more accurately processes that occur inside of the body. Specifically, inclusion of surface His bundle recordings in the clinical electrocardiogram will provide the opportunity for large population surveys of sufficient magnitude to reveal the early natural history of rhythm and conduction problems we have not yet clinically characterized effectively. There is also potential for using the signal enhancement capabilities of the SSNCP in computerized arrhythmia detection systems.

Invention of a neural-cell in 1977 provided the basis to build the first-of-a-kind 4-channel processor in 1979. Though published results (1-4) were significant and outstanding compared to other investigators work. The P1 continued to work to improve the concept and a more advanced 5-channel processor was devised and built in 1980. From about one hundred consecutive beats, in 76 the His bundle signals were identified. It was noticed that during patients inhaling, the signal of interest in most cases disappears. It is possible that the Surface His bundle (SHB) signal gets smaller when the lung is full of air. Some investigators reported the SHB signal varies on the body surface from l x 10^-6 V p-p to 15x10^-6 V p-p from one individual to another. The second generation processor, a 5-channel device was able to detect a signal down to 6x10^-6 V p-p level that helped to achieve a 76% detection of the SHB signal.

The first device, with 4-channels had a sensitivity of only about 9x10^-6 volt p-p. EDR's 8-channel processor is able to detect a signal at least down to 6x10⁷ Vp-p. nearly100% percent of the beats will be measured. 

There are four additional products that have emerged along with the development of the SSNCP processor. A super-low noise preamplifier, a time-variable high-pass filter, a 60Hz digital-comb-reject filter and the new processor or the "brain". In order to perform an auto and cross-correlation and data relationship analysis in real time they are being produced and offered to bio-medical investigators.