Biomedical Engineering Reference
In-Depth Information
of the mock circulatory system mimicked the changes that actually occurred
in the actual living body.
Thus, it seems possible to alter the driving condition of an artificial heart
system so that the artificial heart mimics the change in the function of the
natural heart through the information of the autonomic nervous system. Our
experiment demonstrates the possibility of controlling the driving conditions
of an artificial heart system using sympathetic nervous activity. (Further inve-
stigation is, of course, needed with regard to whether the activity accurately
reflects the systemic hemodynamic conditions.)
An In Vivo Experiment to Control an Artificial Heart System Using
Autonomic Nervous Signals.
Although the in vitro experiment employed
SSNA as the signal for controlling an artificial heart system, it would of course
be desirable to employ the activity of cardiac nerves instead of SSNA for the
purpose of controlling an artificial heart system. As this is impossible to per-
form without invasive procedures, we are currently employing this procedure
in in vivo experiments on animals (goats) that are equipped with a left ven-
tricular assist device (an artificial heart system). We are also trying to control
the driving condition of this artificial heart system by using the signals from
the autonomic nervous system, so that it can mimic the actual changes in
the pumping conditions of a natural heart.
As indicated above, goats were equipped with a left ventricular assist
device. The electrode used in these experiments was a wire electrode made
of stainless steel. It would be desirable to set and fix the electrode to the
cardiac sympathetic nerve; however, in the experiments currently under way,
the electrodes have been fixed to the left vagal and sympathetic nerve trunk
at the neck for technical reasons (Fig. 4.53).
The artificial heart system used in these experiments is the same as that
used in the in vitro experiments (Fig. 4.54). At present, it is not always easy
to measure and record signals of the autonomic nervous system stably from a
goat without preventing it from moving freely, and there still remain several
problems such as:
1. working out a countermeasure against noise;
2. improving the stability and the sensitivity of the nerve electrodes;
3. separating the efferent sympathetic (or parasympathetic) signals from
the afferent signals.
We are currently working on solving these problems.
4.9.3 The Control of Somatic Sensations and the Generation
of Artificial Sensations by Direct Stimulation
of the Neural System
Introduction.
In this section, we discuss a method to evoke artificial soma-
tic sensations by stimulating sensory nerve fibers. The technique is currently
