Pressure and flow have been measured simultaneously at six locations along
the aorta of an anatomically correct 1:1 scale hydraulic elastic tube model
of the arterial tree. Our results suggest a discrete reflection point at t
he level of the renal arteries based on (i) the quarter-wavelength formula
and (ii) the comparison of foot-to-foot (c(ff)) and apparent phase velocity
(c(app)). However, separation of the pressure wave into an incident and re
flected wave at all six locations indicates continuous reflection: a reflec
ted wave is generated at each location as the forward wave passes by. We di
d a further analysis using a mathematical transmission line model with a si
mple tapering geometry (length 50 cm, 31 and 11 mm proximal and distal diam
eter, respectively) for a low (0.32 ml/mmHg), normal (1.6 ml/mmHg) and high
(8 ml/mmHg) value of total arterial compliance. Using the quarter-waveleng
th formula, a discrete reflection point is found at x = 33 cm, the level of
the renal arteries, independent of the value of total compliance. However.
local analysis comparing c(ff) and c(app) does not reveal a marked reflect
ion site, and the analysis of incident and reflected waves merely suggests
a continuous reflection. We therefore conclude that the measured in vivo ao
rtic wave reflection indices are the result of at least two interacting phe
nomena. a continuous wave reflection due to tapering, and local reflections
arising from branches at the level of the diaphragm. The continuous reflec
tion is hidden in the input impedance pattern. Using the quarter-wavelength
formula or the classical wave separation theory, it appears as a reflectio
n coming from a single discrete site, confusingly also located at the level
of the diaphragm, Therefore, the quarter-wavelength formula and the linear
wave separation theory should be used with caution to identify wave reflec
tion zones in the presence of tapering, i.e., in most mammalian arteries, (
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