Age-related impacts of wave transmission at the aorta-carotid bifurcation on local and global measures of arterial stiffness
Authors: Scheuermann Britton , Parr Shannon , Hammond Stephen , Turpin Vanessa-Rose , Kunkel Olivia , Ade Carl 
Published: May 2023

Wave reflections in the periphery have been key in the understanding of aging-related changes in global arterial stiffness, as measured by carotid-femoral pulse-wave velocity (cfPWV). However, recent investigations have demonstrated benefits of using local measures of aortic arch PWV (aaPWV) in addition to considering cfPWV. The contribution of proximal wave reflections at the aorta-carotid bifurcation to aaPWV, as well as to the increasing discordance between aaPWV and cfPWV previously observed with aging, remain poorly understood. The purpose of the present investigation was to examine the impact of transmission of pressure and flow at the aorta-carotid bifurcation on aaPWV and cfPWV in healthy younger and older individuals. We hypothesized that aging-related stiffening of the carotid artery would enhance pressure transmission at the aorta-carotid bifurcation and redirect flow transmission towards a greater relative flow in the distal aortic arch, increasing cfPWV but having minimal impact on aaPWV. We recruited 15 participants, stratified into young adults (YA; n = 8, 4 women; age 20 ± 2.7 years) and older adults (OA; n = 7, 4 women; age 53 ± 2.2 years). Both aaPWV and cfPWV were assessed with ultrasound (Logiq S8, GE Healthcare) via the conventional foot-to-foot velocity waveform method. Carotid artery PWV (caPWV) was calculated using the Bramwell-Hill equation using M-mode scans and carotid pressure waveforms. Carotid, proximal, and distal aortic impedances were derived using estimated blood density, PWV values, and vessel cross-sectional areas. These impedance values allowed for calculation of the pressure and flow transmission coefficients describing the aorta-carotid bifurcation. Sex and BMI were not significantly different between groups (p > 0.05). YA had significantly lower cfPWV (5.2 ± 0.6 vs. 6.8 ± 0.8 m/s, p < 0.05) and caPWV (10.6 ± 0.9 vs. 16.9 ± 1.2 m/s, p < 0.05); however, aaPWV was similar between groups (p > 0.05). This resulted in a reduced pressure transmission coefficient in YA (0.91 ± 0.07 vs. 0.99 ± 0.05, p < 0.05) as well as a greater transmission of flow into the carotid artery relative to the distal aortic arch, represented as the carotid flow transmission coefficient over the distal aortic flow transmission coefficient (0.70 ± 0.20 vs. 0.41 ± 0.1, p <0.05). Linear regression indicated a significant association between caPWV and cfPWV in the entire group, even after adjustment for age, sex and BMI (β = 0.597, p = 0.01) whereas caPWV was not associated with aaPWV in univariate or multivariate analyses. Consistent with our hypothesis, present analyses suggest a role for pressure and flow transmission at the aorta-carotid bifurcation in the dissociation between local stiffness of the proximal aorta (aaPWV) and global arterial stiffness (cfPWV). This highlights the systemic nature of cfPWV, and suggests a need for specificity in the measure of arterial stiffness used and the target outcome of a given study. This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.