Comments on "Exponentially tapered T-tube model of systemic arterial system in dogs"

Identification and physiological relevance of an exponentially tapered tube model of canine descending aortic circulation

The aim of this study was to evaluate the effect of incorporating aortic tapering in a tube model of descending aortic circulation. We described the descending aorta and its peripheral load by an exponentially tapered transmission tube terminating in a first-order, low-pass filter load. Under the assumption of adaptation between the transmission tube and the terminal load, the input impedance of this model was characterized by five free parameters, the characteristic impedance, Zce(0), at the tube entrance; the product, qde, between the tapering factor q and the tube length, de, the product ce(0)de, between the compliance, ce(0), at the tube entrance and the tube length; the time constant, tau ne, of the load and the peripheral resistance, Rp. We estimated these parameters making use of experimental pressure and flow measurements taken from the high descending aorta of three anaesthetized dogs. We contrasted the behaviour of this model with that of a competing model constituted by a uniform transmission tube also terminating in a first-order low-pass filter load. We compared the data fits and, with the aid of an extra measurement of pressure in the abdominal aorta, we tested the congruence between the estimates of the transmission tubes' parameters and the physical and geometrical properties of descending thoracic aorta. The tapered tube model showed a slightly better ability in fitting to experimental flow and reproducing input impedance data. However, the estimates of the transmission tube parameters failed to assess the physical properties of descending aorta. By contrast, the estimates of tube parameters provided by the uniform model allowed location of the junction between the tube and its terminal load in the abdominal aorta at level of major branches. These estimates were well correlated with the real system's properties. In conclusion, the complexity added to the uniform tube model by accounting for exponential aortic tapering gave rise only to a better curve fitting, but did not show any identifiable benefits regarding physiological interpretation of the physical properties of the descending aorta.