Biomedical Engineering Reference
In-Depth Information
Fig. 7.17
The real part of impedance
R
6 evaluated at 6 Hz against the height in healthy (
square
),
asthma before bronchial challenge (
triangle
) and asthma after bronchial challenge (
crosses
). Pre-
dicted values for
R
6 from [
33
](
diamond
)
Fig. 7.18
The percent ratios
FEV
1
/VC
%(
diamond
)and
FEF/VC
%(
square
) against height
Fig. 7.19
Impedance plots
for the healthy children group
QF
6 and the power factor
PF
6aregiveninFig.
7.24
. Finally, the boxplots for the
real part of impedance
R
6 and resonant frequency
η
r
are given in Fig.
7.25
.
There were no significantly different values obtained between the groups for the
hysteresivity
η
r
(
p<
0
.
41), perhaps due to prior medication of the asthmatic group.
Indeed, in lung tissues, the frictional stress is almost invariably between 0.1 and 0.2
of the elastic stress, a fraction known as hysteresivity. This means that for each unit
of peak elastic strain energy that is stored during a cyclic deformation, 10 to 20 %
of that energy is lost irreversibly to heat. This fixed relationship holds at the level of