Background: Non-invasive studies of ascending aortic (AA) impedance, using Doppler flow and carotid tonometry have not confirmed the aging changes demonstrated with invasive electromagnetic flow/micromanometer catheters in humans. Aim: To determine AA impedance from cardiac magnetic resonance imaging (CMRI) flow recorded non-invasively and carotid pressure tonometry, and compare results with previously reported invasive data and realistic arterial model (O’Rourke and Avolio, Circ Res 1980;46;363–372). Methods: Fifty apparently normal subjects (aged 21–70 years; 28 males) underwent velocity-encoded CMRI of the thoracic aorta using a 1.5T system (Signa, GEMS, Waukesha, USA). AA flow was measured non-invasively by subtracting simultaneous forward and backward flow velocity across the AA cross-section. Impedance was determined by relating in modulus and phase, corresponding frequency components of the AA flow waveforms with tonometric carotid pressure waveforms (used as surrogate of AA pressure) and recorded sequentially after CMRI. Data were presented in 5 age groups: 21–30, 31–40, 41–50, 51–60 and 61–70 years. Results: Values of impedance modulus and phase were similar to those previously reported for invasive studies, and with impedance modulus being higher in older than younger subjects up to 3 Hz (reflecting higher peripheral resistance in older subjects, and impedance phase crossed from negative to positive values between 3 and 4.5 Hz. Characteristic impedance (taken as average modulus 5–6 Hz) was 710 dyne.s.cm⁻³. Values of AA impedance fall within the range calculated for a realistic model of the arterial system between age 20 and 80 years. Conclusion: AA impedance values calculated non-invasively from AA CMRI flow waveforms and carotid pressure waveforms show the same pattern as seen with invasive studies in older and younger subjects and lie within the same range as predicted form models at age 20 to 80 years. Better correspondence is expected when AA pressure waveforms can be measured in the magnet room simultaneously with AA flow acquisition.
|Number of pages||2|
|Publication status||Published - 2014|
|Event||Annual Scientific Meeting of the High Blood Pressure Research Council of Australia (HBPRCA) (35th : 2013) / Annual Scientific Meeting of the Australian Atherosclerosis Society (AAS) (39th : 2013) - Melbourne, Australia, Australia|
Duration: 5 Dec 2013 → 7 Dec 2013