Assessment of conceptual inconsistencies in the hybrid reservoir-wave model

The reservoir-wave paradigm separates pressure into windkessel-related `reservoir´ and wave-related `excess´ components, however the conceptual validity of this approach has not been sufficiently scrutinized. This paper assesses two logical implications of the reservoir-wave concept. First, parameters defining the reservoir (resistance and compliance) should be independent of wave effects. Second, wave analysis performed using excess pressure should provide a more accurate and physically intuitive representation of wave propagation and reflection in a vascular system, compared with the traditional wave analysis based on unseparated pressure. These issues were investigated with one-dimensional numerical models. Using a single vessel model, reservoir parameters were shown to be highly influenced by wave propagation effects. In a single bifurcation model, wave analysis based on excess pressure underestimated the reflection coefficient of the known impedance mismatch at the junction, overestimated the distance to this reflection site, and exhibited backward expansion waves suggestive of multiple negative impedance mismatches that did not exist in the system. Traditional wave analysis accurately and intuitively described waves. The identified conceptual inconsistencies in the reservoir-wave paradigm may arise from the use of hybrid (0D and 1D) dimensionality, rather than a hierarchical approach to model dimensionality.