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njit-etd2003-081 - New Jersey Institute of Technology

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142<br />

4.2.8 System Identification Analysis<br />

All the system identification tasks were performed using the commercially available<br />

MATLAB System Identification Toolbox (The MathWorks, Inc.). The physiological<br />

data acquired from COPD and normal subjects were used for building simplified models<br />

<strong>of</strong> complex systems from respiration signals as noisy time-series data. The<br />

mathematical ARX models <strong>of</strong> dynamic cardiovascular systems based on observed<br />

input/output data were obtained. The time and frequency response plots as well as the<br />

pole-zero plots were also acquired. The control parameters <strong>of</strong> the estimated models<br />

such as ARX coefficients, the model order, and the transfer function parameters such as<br />

the overall gain, DC gain, 3 dB points and phase responses were tabulated for each<br />

subject.<br />

4.2.9 Analysis <strong>of</strong> generation <strong>of</strong> Broadband respiration signal<br />

Part <strong>of</strong> the method <strong>of</strong> investigation for noninvasively characterizing the ANS in humans<br />

was to determine the system response at all frequencies <strong>of</strong> interest simultaneously<br />

through the use <strong>of</strong> broadband input waveforms. Berger, Saul, et al. [44] described a<br />

simple method for eliciting a broadband respiration signal without significantly altering<br />

the normal ventilatory mechanics. In their study the broadband respiratory signal was<br />

obtained by instructing the subject to start inhale/exhale as cued by a sequence <strong>of</strong> beeps<br />

(100 ms long), which is generated by a PDP-11/23 computer. The computer programs<br />

then beep evenly at a preset rate 2 0 for a few minutes so that the subject can find a<br />

comfortable depth <strong>of</strong> inspiration. The computer then switches to a mode in which the<br />

beeps were spaced at irregular intervals chosen randomly from a given distribution but

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