Effect of unilateral field stimulation of carotid baroreceptors on vascular impedance and wave reflection in the rat aorta and renal artery

Z. Kouchaki, M. Butlin, E. Lovett, A. Avolio

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    Abstract

    Objective: Carotid baroreceptor stimulation is used for treatment of resistant hypertension, with possible additional effect on the vasculature beyond the associated decrease in arterial pressure. This study aims to quantify the effect of acute baroreceptor stimulation on renal and aortic impedance and wave reflection in rats. Design and method: Male Wistar-Kyoto (n = 9, age 12–56 weeks) were anaesthetised (urethane, 1.3 g/kg) and implanted with a field stimulation electrode (100 Hz, pulse width 0.53 ms) surrounding the left common carotid artery, immediately proximal to the carotid bifurcation. Mean arterial pressure (MAP), heart rate (HR), lower thoracic aorta and renal flow were measured simultaneously. Aortic and renal resistance was calculated using measured pressure (P) and flow (Q) waveforms. For aortic and renal sites, impedance modulus (Zm) and phase (Zph) were calculated as the ratio of Fourier components of P and Q waveforms. Characteristic impedance (Zc) (impedance in the absence of the wave reflection) was determined from the average of harmonics 3 to10 from the impedance frequency spectrum. Forward (Pf) and backward (Pb-) pressure waveforms were computed as Pf = (P + Zc × Q)/2 and Pb = (P-Zc × Q)/2. Reflection magnitude (Rm) was quantified as the ratio of the amplitude of Pb (aPb) and Pf (aPf). Phase zero crossing frequency (fz) and frequency of minimum modulus (fZmin) was determined for aortic and renal impedance spectra. Results: Stimulation caused substantial reduction in MAP and HR accompanied by a tendency for reduction in aortic and renal mean flow (Qm) but no significant change in aortic or renal resistance (Res) (Table, means ± SD). However, there was a significant reduction in aortic but not renal Rm. There was no change in aortic or renal Zc but a general leftward shift of the impedance spectrum as suggested by lower fz and fZmin with stimulation.
    Original languageEnglish
    Article numberPP.12.05
    Pages (from-to)e234
    Number of pages1
    JournalJournal of Hypertension
    Volume33
    Issue numberSupplement 1
    DOIs
    Publication statusPublished - 2015
    Event25th European Meeting on Hypertension and Cardiovascular Protection - Milan, Italy
    Duration: 12 Jun 201515 Jun 2015

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