njit-etd2003-081 - New Jersey Institute of Technology

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The data for all 47 COPD subjects were also analyzed, tabulated and statistically
summarized as shown in table 5.5:
Table 5.5 Gain and Phase Data of COPD Subjects
3dB Gain 3dB Freq Hz -45 (Hz) -90 (Hz) -180 (Hz)
Mean 213.42 0.0857 0.1633 0.6722 93.1328
Std Error 35.84 0.0215 0.0838 0.8285 5.3413
Median 195.11 0.0730 0.0918 0.2356 11.47
STD 181.42 0.0512 0.0633 0.8657 8.8880
Variance 6147.49 0.0048 0511 0.8792 20.4733
Comparing tables 5.4 and 5.5, the 3dB gains and 3dB frequencies of the normal
and COPD subjects are similar. However, all three phase data points at —45, -90 and —
180 degrees of COPD show a significant lag in response time. The lag time is commonly
referred to as propagation time or dead time because no output is produced during this
time.
The gain and phase data obtained from cardiovascular modeling of normal and
COPD show definite changes in the way the baroreflex behaved in normal and COPD
subjects. Since the COPD model represents a disease state, it is obvious that the lag time
affects the stability of a control system. Although lag time in COPD cannot be eliminated
from the model, it may certainly be reduced. In addition, the system loop gain may be
adjusted until the system is stable. This is verified from the fact that the cardiovascular
system still works in COPD and that the COPD 3dB gain is slightly smaller than that of
normal subjects.