The changes experienced by the arterial system due to the aging process have been extensively studied but are incompletely understood. Within-subject patterns of changes in regards to input impedance and wave reflection parameters have not been assessed. The Asklepios study is a longitudinal population study including healthy (at onset) middle-aged subjects, with 974 males and 1052 females undergoing 2 rounds of measurements of applanation tonometry and ultrasound, 10.15±1.40 years apart. Carotid-femoral pulse wave velocity, aortic input impedance, and wave reflection parameters were assessed, and linear mixed-effects models were used to evaluate their longitudinal trajectories and determinants. Overall, the effective 10-year increase in pulse wave velocity was less than expected from first round cross-sectional data, and pulse wave velocity was found to accelerate more in women than in men. Interestingly, the increase in pulse wave velocity was not paralleled by a decrease in arterial volume compliance, particularly in younger males. Aortic root characteristic impedance decreased with age in younger subjects while it increased for the older subjects in the study. These changes suggest that aortic dilation and elongation may play an important role determining the longitudinal age-related changes in impedance parameters in middle-age. Wave reflection decreased with aging, whereas resistance increased in women and decreased in men. We conclude that the effective impact of aging on arterial system properties, in a middle-aged population, is not well reflected by cross-sectional studies. Future studies should assess the interaction between geometric remodeling and wall stiffening as determinants of pulsatile hemodynamics.

The C-Pulse is a novel extra-aortic counter-pulsation device to unload the heart in patients with heart failure. Its impact on overall hemodynamics, however, is not fully understood. In this study, the function of the C-Pulse heart assist system is implemented in a one-dimensional (1-D) model of the arterial tree, and central and peripheral pressure and flow waveforms with the C-Pulse turned on and off were simulated. The results were studied using wave intensity analysis and compared with in vivo data measured non-invasively in three patients with heart failure and with invasive data measured in a large animal (pig). In all cases the activation of the C-Pulse was discernible by the presence of a diastolic augmentation in the pressure and flow waveforms. Activation of the device initiates a forward traveling compression wave, whereas a forward traveling expansion wave is associated to the device relaxation, with waves exerting an action in the coronary and the carotid vascular beds. We also found that the stiffness of the arterial tree is an important determinant of action of the device. In settings with reduced arterial compliance, the same level of aortic compression demands higher values of external pressure, leading to stronger hemodynamic effects and enhanced perfusion. We conclude that the 1-D model may be used as an efficient tool for predicting the hemodynamic impact of the C-Pulse system in the entire arterial tree, complementing in vivo observations.

Objective: Local pulse wave velocity (PWV) can be estimated from the waterhammer equation and is an essential component of wave separation analysis. However, previous studies have demonstrated inaccuracies in the estimations of local PWV due to the presence of reflections. In this study we compared the estimates of local PWV from the PU-loop, ln(D)U-loop, QA-loop and ln(D)P-loop methods along the complete human arterial tree, and analyzed the impact of the estimations on subsequent wave separation analysis. Approach: Estimated values were derived from the numerical outputs (pressure, flow, flow velocity, area and diameter waveforms) of a 1D model of the human circulation, and compared against a reference PWV obtained from the Bramwell-Hill equation in a reference configuration, and in a configuration with lower distensibility representing ageing. Main results: When including all nodes, the overall performance of the methods was poor (correlations and mean differences of R 2 < 0.4 and 3.0 ± 4.1 m s −1 for the PU-loop, R 2 < 0.07 and −0.7 ± 2.3 m s −1 for the ln(D)U-loop, and R 2 < 0.06 and −0.4 ± 2.3 m s −1 for the QA-loop). Focusing on specific sites, the ln(D)U-and QA-loop methods yielded acceptable results in the thoracic aorta and iliac arteries, while the PU-loop method was acceptable at the aortic arch. The reflection-insensitive ln(D)P-loop method performed well over the complete network (R 2 = 0.9 and 0.3 ± 0.3 m s −1 ), as did a previously proposed reflection-correction method for most vascular sites. Large errors in PWV estimation are attenuated in subsequent wave separation analysis, but the errors are site-dependent. Significance: We conclude that the performances of the PU-loop, ln(D)U-loop and QA-loop methods are highly site-specific. The results should be interpreted with caution at all times.