Cardiovascular variability modelling: some fundamental concepts

In parallel with individual analysis of the variability signals, namely; heart rate variability (HRV), blood pressure variation (BPV) and lung volume (LV), illustration of a systemic representation to depict their mutual interactions has been of increasing prominence. Various parametric and nonparametric methods have been employed to find a satisfactory relationship between the variability signals and their origins. However, it seems that some of the fundamental concepts, critical in modelling and identification, have been overlooked in this regard. The main purpose of this paper is the presentation of a conceptual discussion about some of these issues including the large signal and small signal cardiovascular modelling, proper definition of the variability signals, and lumped and distributed modelling