Modeling and parameter estimation of cardiopulmonary dynamics
Two approaches for baroreflex regulation were tested, including a simple 1st-order relationship between R-R interval (RRI) and systolic blood pressure (SBP) and the autoregressive moving average (ARMA) model. Experimental data were obtained retrospectively from 22 patients with chronic airway obstruction before and during breathing through an external resistance. Magnitude and phase relations between arterial blood pressure and pleural pressure were evaluated. The computer model provided good fits to arterial pressure waveforms: correlation coefficients (r) ranging from 0.71 to 0.96 (mean±SD: 0.87±0.06) with a simple 1st-order RRI-SBP model. It was observed that the ARMA model did not further improve the goodness of fit. ^ Other baroreflex pathways through peripheral resistance and ventricular contractility were tested but turned out less important than baroreflex control of heart rate. Also systemic autoregulation which is believed to counteract the arterial baroreflex was incorporated into the computer model. However, the effects were insignificant compared to the heart rate baroreflex function. ^ The effect of changing posture from supine to standing on the heart rate variability (HRV) was studied by applying the power spectral analysis to the EUROBAVAR data set. In the supine lying position, relatively fast vagal activity plays a dominant role, whereas the upright standing position results in vagal inhibition and sympathetic predominance. By using the power spectral analysis, postural change from supine to standing resulted in significant decreases in the indexes of vagal influence on HRV: HF power in both absolute and normalized unit decreased (320 to 121 103ms2 Hz with P < 0.005 and 49 to 37 n.u. with P < 0.005, respectively). Consequently, LF/HF increased from 1.4 to 2.65, P < 0.005. ^ The baroreflex sensitivity (BRS) values were estimated by time sequence method, α-coefficients and transfer gains in LF and HF bands. There was a clear difference between BRS values in the supine and the standing positions with an average supine-to-standing BRS ratio of 2.35±0.4. The BRS estimates using HF components indicated higher values than LF analysis. With the evident decrease in normalized HF power and increase in LF/HF, the effect of changing positions to standing from supine lying can be concluded as a clear reduction in vagal influence on the heart rate variability. ^
"Modeling and parameter estimation of cardiopulmonary dynamics"
Dissertations and Master's Theses (Campus Access).