Systolic Hypertension Mechanisms: Effect of Global and Local Proximal Aorta Stiffening on Pulse Pressure |
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Authors: | Philippe Reymond Nico Westerhof Nikos Stergiopulos |
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Institution: | 1.Laboratory of Hemodynamics and Cardiovascular Technology,Ecole Polytechnique Fédérale de Lausanne,Lausanne,Switzerland;2.Department of Pulmonary Diseases,VU University Medical Center,Amsterdam,The Netherlands |
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Abstract: | Decrease in arterial compliance leads to an increased pulse pressure, as explained by the Windkessel effect. Pressure waveform
is the sum of a forward running and a backward running or reflected pressure wave. When the arterial system stiffens, as a
result of aging or disease, both the forward and reflected waves are altered and contribute to a greater or lesser degree
to the increase in aortic pulse pressure. Two mechanisms have been proposed in the literature to explain systolic hypertension
upon arterial stiffening. The most popular one is based on the augmentation and earlier arrival of reflected waves. The second
mechanism is based on the augmentation of the forward wave, as a result of an increase of the characteristic impedance of
the proximal aorta. The aim of this study is to analyze the two aforementioned mechanisms using a 1-D model of the entire
systemic arterial tree. A validated 1-D model of the systemic circulation, representative of a young healthy adult was used
to simulate arterial pressure and flow under control conditions and in presence of arterial stiffening. To help elucidate
the differences in the two mechanisms contributing to systolic hypertension, the arterial tree was stiffened either locally
with compliance being reduced only in the region of the aortic arch, or globally, with a uniform decrease in compliance in
all arterial segments. The pulse pressure increased by 58% when proximal aorta was stiffened and the compliance decreased
by 43%. Same pulse pressure increase was achieved when compliance of the globally stiffened arterial tree decreased by 47%.
In presence of local stiffening in the aortic arch, characteristic impedance increased to 0.10 mmHg s/mL vs. 0.034 mmHg s/mL
in control and this led to a substantial increase (91%) in the amplitude of the forward wave, which attained 42 mmHg vs. 22 mmHg
in control. Under global stiffening, the pulse pressure of the forward wave increased by 41% and the amplitude of the reflected
wave by 83%. Reflected waves arrived earlier in systole, enhancing their contribution to systolic pressure. The effects of
local vs. global loss of compliance of the arterial tree have been studied with the use of a 1-D model. Local stiffening in
the proximal aorta increases systolic pressure mainly through the augmentation of the forward pressure wave, whereas global
stiffening augments systolic pressure principally though the increase in wave reflections. The relative contribution of the
two mechanisms depends on the topology of arterial stiffening and geometrical alterations taking place in aging or in disease. |
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