Informational analysis of left-ventricle/systemic-arterial interaction

Studies of left ventricle (LV) and systemic arterial (SA) interaction can be grouped into four categories: 1) prediction of pressure and flow waveforms, 2) changes in LV/SA function with changes in SA properties, 3) identification of criteria that reveal matching between LV and SA properties, 4) definition of LV afterload. Whereas results from studies in categories 1, 2, and 3 reveal the consequences of interaction, results from studies in category 4 come closest to revealing the true character of LV/SA interaction. A useful description arising from category 4 is that of a circular feedback path connecting LV outflow, SA input-impedance, LV pressure, and LV pump properties. The identification of a node in this scheme results in the separation of LV functions into active functions and loading functions and the separation of LV/SA load into LV load and SA loading elements. The time-varying LV elastance participates in both LV active functions and LV loading functions, with the former dominating the latter. Total peripheral resistance dominates all other LV and SA loading elements in its loading effects. Although an elastance-resistance LV model coupled with a simple second-order SA load model accounts for many reported observations on LV/SA interaction, data from sudden aortic occlusion studies indicate a need to consider yet another interaction action. Evidence is presented to suggest the existence of an LV pump element that couples ejection events with relaxation and filling events.