Biomedical Engineering Reference
In-Depth Information
heater B is turned on and the outer arm opens to be a flat shape so that it can release the
blood vessel safely. The temperature of the heaters exceeds 65°C, which is equal to the
deformation temperature of the SMA film, within several seconds by the electric heating. It
seems a short time enough for actual use in the body without serious biological damage.
A laboratory rat is chosen for the evaluation of pulsation monitoring. A femoral artery
of a laboratory rat was held between the outer arm and the cantilever of the sensor to
evaluate real-time blood pulsation waveform. The outer diameter of the examined artery
was about 1 mm. Change in blood pulsation waveform was measured when bloodstream
was obstructed by clamping of the artery from outside intermittently as shown in Figure
9.64 (Mineta et al., 2008). The result of the waveform measurement is shown in Figure
9.65. When the blood flowed normally, periodical output voltage with amplitude of about
3.5 mV was obtained. Not only swelling but also shrinking of the artery was observed
during each pulse cycle. Frequency of the waveform well agreed with a pulse period of a
rate of 180 pulses/min. On the other hand, amplitude of the output voltage decreased to
1 mV when the bloodstream was obstructed by a mechanical clamping from outside the
artery. As the results of the examination, it is confirmed that the developed sensor is sen-
sitive enough to distinguish the bloodstream obstruction from the normal arterial blood
pulsation.
The sensor could detect static deflections with a sensitivity of 0.1 mV/
μ
m or larger with
the sensing cantilever of the SMA film. The sensor could also detect the waveform of the
pulsation when the dynamic diameter change of the held tube was 15
μ
m or larger. In
addition, the sensor was successfully applied to an in vivo examination using a femoral
artery of a laboratory rat. When the bloodstream of the artery of the rat was obstructed,
decrease in amplitude of pulsation waveform was detected clearly. The sensor was fabri-
cated based on simple photofabrication processes, which provide a possibility of inexpen-
sive disposable devices.
OP amp.
(Gain: × 10)
Signal recording
Femoral artery
Microvascular
clamp
FPC
Femoral vein
Sensor
FIGURE 9.64
Scheme of laboratory rat examination. (From Mineta et al.,
Sens. Actuators A Phys.
, 143, 14-19, 2008, with permis-
sion from Elsevier.)
