Biomedical Engineering Reference
In-Depth Information
Fig. 9.7
BLA of the calibration tube:
left
the commercial device,
right
the prototype device.
Bold
black line
:BLA;
blue dashed line
: total variance (noise
stochastic non-linear distortion);
red
dotted line
: noise variance;
green dash-dot line
: variance of the stochastic non-linear distortion
with respect to one multisine realization
+
commercial and the prototype device is due to difference in tubing length between
the actuator and the mouthpiece.
Next, the BLA of the calibration tube has been estimated, and Fig.
9.7
shows a
significant improvement by reducing the noise and non-linear contributions below
4 Hz. Although the prototype has higher level of noise at higher frequencies, this is
not significant, since we do not intend to use the device for high frequencies. For
the evaluation of the non-linear distortions present in the respiratory system, the
measured non-linear distortions from the generator alone will be taken into account
for correcting the final result in measured volunteers.
9.3 Clinical Markers for Quantifying Non-linear Effects
In order to quantify these non-linear contributions, let us introduce the following
index:
P
even
+
P
odd
P
exc
U
exc
U
even
+
U
odd
T
=
ยท
(9.26)
where each variable is the sum of the absolute values of all the contributions in pres-
sure signal and input flow signal, respectively, at the even non-excited frequencies,
the odd non-excited frequencies and the excited odd frequencies. Only the corrected
output pressure has been taken into account when calculating (
9.26
).
