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Pulse-wave model of brachial arterial pressure modulation in aging and hypertension.

We apply a pulse-wave theory to a model of the human arm arterial system that predicts the changes in the arterial pressure waveform as it traverses the vasculature (increased pulse pressure, sharper main wave, disappearance of the aortic incisura, and appearance of a diastolic dicrotic wave) and also predicts the observed modulation of the waveform during phenylephrine-induced vasoconstriction and nitroglycerin-induced vasodilation. The model considers the arm arterial system as a tapered, distensible tube that bifurcates and then ends in a loop, with sidebranch networks represented by distributed Windkessels. The model uses verifiable values for realistic parameters. We found that the vertical modulation of the dicrotic wave, in humans, decreased with advancing age and with high blood pressure. The model explained these findings in terms of increasing vascular rigidity and decreasing small vessel vasodilator responsiveness. We noted a significant negative correlation between the arterial level of plasma norepinephrine and the amount of modulation of the dicrotic wave after nitroglycerin among subjects 40 yr old or younger, suggesting a sympathetic neurogenic contribution to the vascular abnormalities observed in relatively young patients with essential hypertension.