Modified asymmetric T-tube model to infer arterial wave reflection at the aortic root.

A modified version of the T-tube model was constructed to represent the systemic arterial loading system as "seen" by the left ventricle (LV). This model consisted of two uniform tubes connected in parallel. It differs from the original T-tube model in that the transmission paths have no frictional losses and are terminated with complex impedances, rather than simple resistors. To estimate model parameters (load and tube compliances, tube inertances, characteristic impedances, and peripheral resistances) we measured ascending aortic pressure and flow in a group of five open-chest, anesthetized dogs. Parameter estimates were obtained by fitting experimental pressure to the pressure predicted by the model from experimental flow. To check the reliability of the model, an additional experiment was performed where flow in the upper descending thoracic aorta was measured in addition to ascending aorta pressure and flow. The fit between the experiment and model predicted ascending aortic pressure was satisfactory in all six dogs. This pressure was always characterized by the presence of a prominent diastolic oscillation. Our model showed that this oscillation is due to reflections from the lower body, the effective reflection site being most probably located at the level of middle to low abdominal aorta. The effective reflection site located in the upper body is closer to the heart. The related reflected wave affects pressure in late systole.