Biomedical Engineering Reference
In-Depth Information
Power spectral density of CBV (HbT)
10
5
Age: 25 years
2
0
-2
0
100
200
Time, [s]
10
0
10
-4
10
-3
10
-2
10
-1
10
0
10
5
Age: 63 years
5
0
-5
0
100
200
Ti
m
e, [s]
10
0
10
-4
10
-3
10
-2
10
-1
10
0
Frequency, [Hz]
Fig. 2.5. Cerebral blood volume (CBV) fluctuation patterns (inserts) and their corre-
spondingbimodalspectrainayoungandanoldwoman. The correlated, i.e. self-similar,
fractal pattern is seen in the low frequencies with
β
=1.27 and 1.55, respectively, while
an uncorrelated, noisy dynamics dominates above this frequency range with
β
≈
0
. The
aging process increases the noisy domination in CBV dynamics by shifting the range of
the noisy dynamic from 0.146-1 Hz to 0.014-1 Hz.
Given that low and very low frequency oscillations can likely
be associated with segmental vasomotion rhythms, alterations
observed in the CBV fluctuation spectrum via its spectral index
or specific frequencies deviating from the fractal pattern can be
indicative of a cerebral vascular segment(s) undergoing stiffen-
ing. The process of vessel wall stiffening may arise from loss
of segmental control as manifested by the altered segmental
rhythms.
