Biomedical Engineering Reference
In-Depth Information
not yet been developed, although several methods have so far been proposed
and tried [179,180].
In this section, we discuss the possibility of developing an artificial heart
system that takes information from the autonomic nervous system of the
living body and can control the driving conditions of an artificial heart system
using autonomic nervous activity, so that the artificial heart works optimally.
In Vitro Experiment to Control an Artificial Heart System Using
Skin Sympathetic Nervous Signals.
It has been reported that emotional
stress or various kinds of nociceptive stimuli to the sensory receptors at the
skin or viscera provoke increases in heart rate and peripheral vascular resi-
stance, and augmentation of the contractility of the heart through changes
in the activities of the sympathetic nervous system (the cardiac sympathe-
tic nerve-accelerator) and the parasympathetic nervous system (the cardiac
branch of the vagal nerve-suppressor) by reflex.
In this study, we attempted to reproduce the change that takes place
in the actual hemodynamics of the living body when nociceptive stimuli are
given to a subject. To that end, we used a mock circulatory system connected
to an artificial heart system, and tried to control the driving condition of the
artificial heart system by using information from the sympathetic nervous
activity.
In this experiment, we used skin sympathetic nerve activity (SSNA) as
the parameter to determine the condition of the artificial heart system. SSNA
includes the activities of the sympathetic nerve fibers that are contained in a
peripheral nerve and involve the vasomotor and sudomotor functions at the
skin area.
Although this activity is directly concerned with cardiac function, the
first and most important reason for selecting SSNA is that, at the moment,
it is the only sympathetic nervous activity that can be measured from awake
and nonanesthetized human subjects. The second reason is that, as SSNA
concerns the activity of a vasoconstrictor, a change in SSNA seems to reflect
a change in the peripheral vascular resistance or peripheral blood flow.
It has generally been accepted that the discharge of a vasomotor nerve
fiber burst accelerates the constriction of peripheral blood vessels, and that
the increase in this activity causes an increase in the peripheral resistance
and consequently in the peripheral blood pressure [181,182]. The number of
SSNA bursts counted using a pulse counter was therefore used as the parame-
ter to determine the driving condition of the pneumatically driven artificial
heart system connected with a mock circulatory system with a peripheral
resistance.
The Experimental Arrangement.
The experimental arrangement is
shown in Fig. 4.51. The subject sat in an armchair in a fairly relaxed po-
sture throughout the experiment. The measurements included blood flow
