Biomedical Engineering Reference
In-Depth Information
aqueous milk solutions (50% and 25%) were pumped with a motorized syringe in the
microtube with the simulated velocities during ten minutes with Perimed probe posi-
tioned perpendicular to the surface of the phantom. The mean perfusion, in perfusion
units (PU), for each velocity and concentration was computed for three minutes of blood
perfusion signal and a linear regression study was performed.
Skin Measurements.
Measurements in the ventral side of the forearm, in 20 healthy
non-smoking subjects, in the supine position, and the limb at heart level were performed
(age 24.7
±
4.2 years old, range 19-39 years old; 11 females; arterial pressure: min 7.1
±
2.3). All subjects were Caucasian, except
one female. The participants did not take any vasoactive medication and were asked to
refrain from drinking coffee during the measurement tests. The tests were performed in
a quiet room, where the temperature varied between 22 and 25
◦
C
. Motility standard
calibrations were performed before each measurement. The Ethics Committees of the
Centro Cirúrgico de Coimbra (CCC) in Portugal, approved this study. Informed consent
was obtained from the subjects before the recordings were performed.
Perfusion was recorded during thirty three minutes: baseline blood flux was recorded
for 20 min. Then, an arterial occlusion test was performed with a pressure cuff placed
around the upper limb, inflated for 3 min at 200 mm Hg in order to obtain the biological
zero (BZ). The cuff was then released to obtain a post-occlusive reactive hyperemia
and the signal was recorded during 10 min after the release of the occlusion. For each
subject, the protocol was repeated using the three laser diodes existing in the prototype:
635, 785, and 830 nm.
Quantitative data were expressed as the median (first quartile, second quartile). The
normal distribution of the data was evaluated (using Shapiro-Wilk statistics). The ma-
jority of the data of the different parameters were not normally distributed. Therefore,
non parametric tests were used. The Wilcoxon test was used to test for significant dif-
ferences between results obtained with different laser wavelengths, different emitting-
receiving fibre distances and skin regions. Analysis was performed with SPSS v.17.0
for WINDOWS (SPSS Inc, Chicago, IL, USA). The results were considered statisti-
cally different for p-values lower than 0.05.
0.8 mmHg, max 11.4
±
1; IMC: 22.1
±
Rat Brain Measurements.
In vivo
tests were performed in male Wistar rats (9 weeks).
Rats were anesthetized with urethane (1.25 g/kg, i.p.), and placed in a stereotaxic frame
(Stoelting Co, USA). After having exposed the rat brain surface and removed the dura
mater, one of the microprobes was stereotaxically inserted into the hippocampus. To-
gether with our probe we inserted a commercial laser Doppler needle probe (Perimed
reference: PF411; outer diameter, 450
μm
; fibre separation, 150
μm
; wavelength, 780
nm) connected to a laser Doppler flowmeter device (Periflux system 5000, Perimed,
Sweden), in the opposite cerebral hemisphere. The simultaneous use of the probes al-
lows the comparison of the signals acquired by our probes with the one of the commer-
cial flowmeter probe. Measurements were made with the 785 nm micro-probe. After the
probes implantation, a baseline was recorded during c.a. 5 minutes and then sodium ni-
trite (200 mg/kg in saline solution) was intraperitoneally injected, in order to induce
metahemoglobinemia and finally cardiac arrest. The correlation between the results ob-
tained with the Perimed probe and with both micro-probes was computed. The signals
were normalized before the cross-correlation analysis.
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