Longitudinal Changes of Input Impedance, Pulse Wave Velocity, and Wave Reflection in a Middle-Aged Population: The Asklepios Study.

[Figure: see text].

Correction: A 1D computer model of the arterial circulation in horses: An important resource for studying global interactions between heart and vessels under normal and pathological conditions.

[This corrects the article DOI: 10.1371/journal.pone.0221425.].

A 1D computer model of the arterial circulation in horses: An important resource for studying global interactions between heart and vessels under normal and pathological conditions.

Arterial rupture in horses has been observed during exercise, after phenylephrine administration or during parturition (uterine artery). In human pathophysiological research, the use of computer models for studying arterial hemodynamics and understanding normal and abnormal characteristics of arterial pressure and flow waveforms is very common. The objective of this research was to develop a computer model of the equine arterial circulation, in order to study local intra-arterial pressures and flow dynamics in horses. Morphologically, large differences exist between human and equine aortic arch and arterial branching patterns. Development of the present model was based on post-mortem obtained anatomical data of the arterial tree (arterial lengths, diameters and branching angles); in vivo collected ultrasonographic flow profiles from the common carotid artery, external iliac artery, median artery and aorta; and invasively collected pressure curves from carotid artery and aorta. These data were used as input for a previously validated (in humans) 1D arterial network model. Data on terminal resistance and arterial compliance parameters were tuned to equine physiology. Given the large arterial diameters, Womersley theory was used to compute friction coefficients, and the input into the arterial system was provided via a scaled time-varying elastance model of the left heart. Outcomes showed plausible predictions of pressure and flow waveforms throughout the considered arterial tree. Simulated flow waveform morphology was in line with measured flow profiles. Consideration of gravity further improved model based predicted waveforms. Derived flow waveform patterns could be explained using wave power analysis. The model offers possibilities as a research tool to predict changes in flow profiles and local pressures as a result of strenuous exercise or altered arterial wall properties related to age, breed or gender.

Mapping the site-specific accuracy of loop-based local pulse wave velocity estimation and reflection magnitude: a 1D arterial network model analysis.

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.

Hemodynamic Impact of the C-Pulse Cardiac Support Device: A One-Dimensional Arterial Model Study.

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.