Biomedical Engineering Reference
In-Depth Information
Fig. 9.10
Photo and schematic setup of the novel FOT device for low-frequency impedance mea-
surement
non-linear distortions (after the feedforward compensation) and the disturbances re-
sulting from the subjects breathing are suppressed by a feedback control loop, a
simple proportional-integral (PI) control.
By applying these compensations, one can excite the respiratory properties of
the patient with a random phase multisine with a random harmonic grid and a flat
power spectrum in the frequency band 0
.
1-5 Hz. By use of a flat power spectrum,
a constant SNR can be obtained over the whole frequency band, as observed from
Fig.
9.11
. More details about the design of multisine signals for frequency domain
identification can be found in [
136
].
9.5.2 Respiratory Impedance at Low Frequencies
With the novel device available, measurements have been performed on healthy
children, adults, and diagnosed patients with asthma and with COPD. The biomet-
ric data for the healthy groups are given in Table
9.1
, whereas those for the diag-
nosed groups are given in Table
9.2
. The COPD is further classified according to the
GOLD standard in several levels of disease severity, as given in Table
9.3
.
