Time-domain representation of ventricular-arterial coupling as a windkessel and wave system

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Abstract
The differences in shape between central aortic pressure (PAo) and flow waveforms have never been explained satisfactorily in that the assumed explanation (substantial reflected waves during diastole) remains controversial. As an alternative to the widely accepted frequency-domain model of arterial hemodynamics, we propose a functional, time-domain, arterial model that combines a blood conducting system and a reservoir (i.e., Frank's hydraulic integrator, the windkessel). In 15 anesthetized dogs, we measured PAo, flows, and dimensions and calculated windkessel pressure (PWk) and volume (VWk). We found that PWk is proportional to thoracic aortic volume and that the volume of the thoracic aorta comprises 45.1 ± 2.0% (mean ± SE) of the total VWk. When we subtracted PWk from PAo, we found that the difference (excess pressure) was proportional to aortic flow, thus resolving the differences between PAo and flow waveforms and implying that reflected waves were minimal. We suggest that PAo is the instantaneous summation of a time-varying reservoir pressure (i.e., PWk) and the effects of (primarily) forward-traveling waves in this animal model.
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