Summary
Objectives
: This paper describes the development of a model-based approach to estimating both
open-loop and causal time-varying coherence functions (TVCF). Theoretical derivations
of the coherence bounds using the proposed approach are also provided.
Methods
: A time-varying vector autoregressive (VAR) model was used to estimate both open-loop
and causal TVCF. The time-varying optimal parameter search method was employed to
identify the time-varying model coefficients as well as the model order of the VAR
model.
Results
: Simulation results revealed interesting observations, and they were corroborated
using experimental renal blood pressure and flow data. Specifically, experimental
data showed that in certain cases, the calculation of the open-loop TVCF might provide
incorrect interpretation of the results when the system under investigation was a
closed-loop system, which is consistent with theoretical derivations.
Conclusions
: The use of the closed-loop TVCF not only provides quantitative assessment of the
coupling between the two signals, but it also provides valuable insights into the
composition of the physical structure of the system.
Keywords
Causal coherence - coherence - myogenic - TGF - time-varying
