Biomedical Engineering Reference
In-Depth Information
Fig. 8.22
The information
extracted for each patient in
terms of
C
and
F
d
from the
PV plots
Fig. 8.23
The information
extracted for each patient in
terms of
C
and
F
d
from the
PPP plots
We have as a result
V(t)
C
r
P(t)
=
R
r
·
Q(t)
+
(8.25)
This represents the first order equation in the motion-equation for a single com-
partment model of the respiratory system: a single balloon with compliance
C
r
on
a pipeline with a resistance
R
r
. This system can be studied using the exponential
decay of volume
V(t)
as resulting from a step input
V
0
:
V(t)
V
0
e
−
t/τ
, where
t
is time and
τ
is the time constant which characterizes the system, denoted by the
product of
R
r
C
r
[
116
].
In the representation of the PPP plots, we have the breathing signal expressed
as pressure and its time-delayed derivative. From (
8.25
) can be observed that there
exists a relation between pressure and flow (
Q(t)
=
dV/dt
). In clinical terms, the
pressure-volume loop during one breathing period is able to tell the clinician some-
thing about the dynamic compliance of the respiratory system and its work. The
area enclosed by the PV loop is called the physiologic work of breathing, denoting
the resistive work performed by the patient to overcome the resistance present in the
airways [
134
].
=
