Biomedical Engineering Reference
In-Depth Information
4.7.3
The Technique of Microneurography
As mentioned above, microneurography involves percutaneous and direct in-
sertion of a very thin tungsten microelectrode (needle type) into a peripheral
nerve to measure the signal of the nerve fiber attached to the tip of the elec-
trode and to make it possible to stimulate nerve fibers that are attached to
the tip of the electrode (microstimulation).
With respect to the tungsten microelectrode, the diameters of the shaft
and the tip are around 120
m, respectively, and when the tip
of the electrode (where the electrical insulation by epoxy resin is removed)
is properly attached to only one nerve fiber, it is possible to record signals
from a single nerve fiber (Fig. 4.32) and to stimulate a single nerve fiber
electrically.
The procedure of microneurography that we are currently adopting is
based on that of the Nagoya University group under the direction of Professor
T. Mano. This research group has played a leading part in the introduction
and establishment of this technique in Japan.
The procedure is described below.
Extremely fine tungsten microelectrodes (needle electrodes) are used as
working electrodes. One is inserted percutaneously into a peripheral nerve.
A reference electrode is attached to the surface of the skin with paste, a few
centimeters away from the point of insertion of the working microelectrode.
Although percutaneous electrical stimulation is usually used to search
for the direction of the objective nerve, we use ultrasonography to confirm
the position of the tip of the needle electrode and that of the target nerve
trunk. Using an ultrasonic probe with a comparatively high frequency (we are
currently using an annular alley probe with a frequency of 7.5 MHz), normal
peripheral nerves at the extremities (in the transverse section) are displayed
in a circular area circumscribed by a high-intensity linear structure, and this
circular area contains high-intensity microtubular structures (Fig. 4.33). By
watching the spatial relationship between the position of the tip of the needle
electrode and the objective peripheral nerve, it is easy to make the top of
the microelectrode reach the surface of the target nerve. Furthermore, it
is possible to set the tip of the needle electrode at any desired position in
the nerve trunk (Fig. 4.34). It is easy to judge when the needle electrode is
actually inserted into the peripheral nerve, because a subject usually reports
a particular sensation when the electrode is inserted.
The measured nerve activities are amplified through a preamplifier, after
which they are passed through a band-pass filter (300-5000 Hz), displayed
on an oscilloscope, and finally amplified around 50 000 times. At the same
time, the nerve signals are connected to a loudspeaker so that they can be
audibly monitored (Fig. 4.35).
Electrical stimulation of the nerve fiber can also be performed through
the same microelectrodes by changing the circuit from a measurement mode
to a stimulation mode using a switch box.
mand10
μ
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