Table of Contents
An active electrode for biopotential recording from small localized bio-sources
Emil S Valchinov and Nicolas E Pallikarakis
Department of Medical Physics, University of Patras, Patras 26500, Greece
BioMedical Engineering OnLine 2004,
3:25doi:10.1186/1475-925X-3-25. [an open-access article]
Abstract
Background
Laser bio-stimulation is a well-established procedure in Medical
Acupuncture. Nevertheless there is still a confusion as to whether it
works or the effect is just placebo. Although a plethora of scientific
papers published, showing positive clinical results, there is still a
lack of objective scientific proofs about the bio-stimulation effect of
lasers used in Acupuncture. The objective of this work was to design
and build a body surface electrode and an amplifier for biopotential
recording from acupuncture points, considered here as small localized
bio-sources (SLB). The design is aimed for studying SLB potentials
provoked by laser stimulus, in search for objective proofs of the
bio-stimulation effect of lasers used in Medical Acupuncture.
Methods
The active electrode presented features a new adjustable anchoring
system and fractionation of the biopotential amplifier between the
electrode and the cabinet’s location. The new adjustable electrode
anchoring system is designed to reduce the electrode-skin contact
impedance, its variation and motion artifacts. That is achieved by
increasing the electrode-skin tension and decreasing its relative
movement. Additionally the sensing element provides local constant skin
stretching thus eliminating the contribution of the skin potential
artifact. The electrode is attached to the skin by a double-sided
adhesive pad, where the sensing element is a stainless steel, 4 mm in
diameter. The fractionation of the biopotential amplifier is done by
incorporating the amplifier’s front-end op-amps at the electrodes, thus
avoiding the use of extra buffers. The biopotential amplifier features
two selectable modes of operation: semi-AC-mode with a -3 dB bandwidth
of 0.32–1000 Hz and AC-mode with a bandwidth of 0.16–1000 Hz.
Results
The average measured DC electrode-skin contact impedance of the proposed electrode was 450 kΩ, with electrode tension of 0.3 kg/cm2 on
an unprepared skin of the inner forearm. The peak-to-peak noise voltage
measured at the amplifier output, with input terminals connected to
common, was 10 mVp-p, or 2 μVp-p referred
to the input. The common-mode rejection ratio of the amplifier was 96
dB at 50 Hz, measured with imbalanced electrodes’ impedances. The
prototype was also tested practically and sample records were obtained
after a low intensity SLB laser stimulation. All measurements showed
almost a complete absence of 50 Hz interference, although no
electrolyte gel or skin preparation was applied.
Conclusion
The results showed that the new active electrode presented
significantly reduced the electrode-skin impedance, its variation and
motion artifact influences. This allowed SLB signals with relatively
high quality to be recorded without skin preparation. The design offers
low noise and major reduction in parts, size and power consumption. The
active electrode specifications were found to be better or at least
comparable to those of other existing designs.