Biomedical Engineering Reference
In-Depth Information
Ta b l e 8 . 4
Fitted power-law
models (
8.23
) for each group
of data. COPD: chronic
obstructive pulmonary
disease. KS: kyphoscoliosis.
CF: cystic fibrosis
DATA source
A
PV/PPP
B
PV/PPP
Healthy adults
0.632/0.848
0.094/0.062
COPD
0.752/0.795
0.069/0.068
KS
0.882/0.844
0.062/0.067
Healthy children
0.557/0.704
0.127/0.090
Asthma
0.624/0.739
0.114/0.087
CF
0.478/0.640
0.147/0.104
As already explained in previous chapters, during cycling loading, the stress that
develops in the viscoelastic body (respiratory tissue) displays:
•
a component in phase with strain, which is the elastic stress contributing to the
storage modulus
E
S
(elastance); and
•
a component out of phase with strain, corresponding to the viscous dissipation
and contributing to the loss modulus
E
D
(damping).
In [
9
,
26
] was shown that the respiratory system can be indeed modeled as a
combination of series RC elements in a cascade arrangement of consecutive airways,
by using their mechanical analogue representation, springs
K
rs
and dashpots
B
rs
.In
this mechanical model, it follows that the pressure-volume relationship equivalent
to the stress-strain relationship is given by
K
rs
rs
A
rs
B
rs
rs
A
rs
dV(t)
dt
P(t)
=
V(t)
+
(8.26)
with
P
the air-pressure,
V
the air volume,
rs
and
A
rs
the changes in length and
area of airways during the breathing cycle, and
K
rs
,B
rs
the constants of the spring
and dashpot, respectively [
26
]. This relation suggests that the PPP loop is a measure
Fig. 8.24
The plot of the identified
A
and
B
values from model (
8.23
) for each set of data
