Biomedical Engineering Reference
In-Depth Information
ject and the onset of an SSNA burst and that between the onset of an SSNA
burst and the time when the hemodynamic parameters began to change were
studied. Based on these results, a program was developed to estimate the
vascular response caused by the change in the number of SSNA pulses, to
alter the driving condition of an artificial heart system in accordance with the
change in the estimated vascular response, and consequently to change the
hemodynamic parameters of the mock circulatory system so that it mimics
the changes in the subject's actual hemodynamics.
Next, the time series data recorded for the SSNA under various stimuli
were inputted into the computer, and the driving parameters of the artificial
heart system (the values of beating rate, positive pressure, and vacuum pres-
sure) were determined and altered using this program in accordance with the
deviation of the counted SSNA number from the control value, and the he-
modynamic parameters of the mock circulatory system were compared with
the actual change in the hemodynamic parameters of the subjects when the
subjects were exposed to the various stimuli.
Here, the control program is not described in detail for the sake of brevity,
and the method of determining the driving parameters of the artificial heart
system (the values of pumping rate, positive pressure, and vacuum pressure)
is briefly outlined below.
First, SSNA(
T
), the index of the SSNA level to determine the driving
conditions of the artificial heart at time
T
(s), was determined as the weighed
summationoftheSSNAnumberfrom2.5sto7.5sbeforetime
T
, giving
consideration to the lapse until the onset of the SSNA burst. Next, the driving
parameters of the pneumatically driven artificial heart system (the values of
the beating rate, positive pressure, and vacuum pressure) were determined
and altered in accordance with the deviation of the SSNA index from the
control value (an average value of SSNA(
T
) when the subject was sitting in
an armchair in a fairly relaxed manner), and the driving condition of the
artificial heart system was altered every 3 s.
Figure 4.52 shows an example of the results of this control. The upper
part of Fig. 4.52 shows the changes with respect to time in SSNA (discri-
minated wave, integrated wave, and number of pulses), the skin blood flow
at the finger, and the digital arterial pressure of a subject when the subject
was repeatedly exposed to unpleasant white noise. The time at which each
stimulation was given to the subject is indicated at the top.
As can be seen in this chart, an increase in SSNA bursts (activation of the
sympathetic nervous system) was observed after the subject received audi-
tory stimulation due to the unpleasant white noise; consequently, the digital
arterial pressure increased, and the skin blood flow at the finger decreased.
The lower part of Fig. 4.52 shows the driving condition of the artificial heart
system and the arterial pressure of the mock circulatory system. The positive
pressure, vacuum pressure, and pumping rate of the artificial heart system
