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Wave reflection sites of arterial systems refer to the areas in which there is an increased load of aortic systolic pressure. The aortic input impedance is a classical method to determine these sites but it is limited to predicting distance and not the amplitude of wave reflections. Herein, a new method based on the separation of pressure and flow waves into their forward and backward running components is tested for identifying the location, distance and amplitude of wave reflections. Simulation experiments to demonstrate the method in mongrel dogs are presented.

A new separation technique has been developed to determine the forward and backward running arterial pressure wave components. It takes into account friction as well as nonlinear effects due to convective acceleration and to the pressure dependence of the arterial compliance. The new method is a combination of two methods treating friction and nonlinearities separately. The method requires the measurements of pressure and flow at one location as well as the knowledge of the area-pressure relationship. The validity of the method was tested by a simulation experiment in which the forward and backward waves were known a priori. It was shown that the new method is significantly more accurate in the predictions of the forward and backward waves when compared to the classical method assuming linearity and no dissipation. The new wave separation method was also applied to simulated aortic waves for (a) a healthy subject and (b) a subject with decreased compliance. Comparison with the classical linear method showed that neglecting nonlinearities leads to an overestimation of the forward and backward pressure wave amplitudes. The errors, however, were in the order of 5 to 10 percent. We concluded that, for most clinical purposes, the improvement using the nonlinear method is of the same magnitude as experimental errors, and thus the linear method would suffice.

This study examined the effects of modification of dense-grade asphalt mixtures with chemically engineered crumb rubber (ECR) via the dry process. The ECR mixtures were compared to unmodified and polymer-modified mixtures in various criteria. The study mainly had three objectives: (1) comparison of mixture performance, (2) investigation of warm mix equivalence, i.e., to determine if the chemical coating on the ECR resulted in benefits similar to warm mix additives, and (3) to determine the effects of ECR on mixture draindown. For the first objective, the disk-shaped compact tension test was conducted to determine resistance to thermal cracking, and the Hamburg wheel tracking test was performed to determine resistance to permanent deformation (rutting) and moisture damage. To fulfill the second objective, the mixtures were prepared with warm mix asphalt (WMA) additives wherever necessary, and for the third objective, a stone mastic asphalt (SMA) was employed instead of the dense-grade mixture that was used for the rest of the study. Findings showed that modification with ECR greatly improved resistance to rutting and cracking, indicating that ECR pavements will exhibit longer service life. In terms of warm mix equivalence, a comparison of volumetrics data showed that ECR without WMA additive compacted in a similar manner as a polymer (PG 76-22) mixture containing WMA additive. Additional mix cost savings may be realized with ECR modification because of the ability to avoid the cost of WMA additive for the goal of achieving mix workability and compaction at lower temperatures. Finally, an ECR-SMA mix was used for draindown assessment and was found to pass the draindown test without the need for fibers, nearly matching the draindown resistance of the polymer-WMA mix containing cellulose fibers, thereby presenting another cost-saving avenue for contractors. The study also includes details of three field projects that used ECR and reported excellent field performance. [ABSTRACT FROM AUTHOR]

Alterations in the input impedance spectrum during changes in heart rate and aortic flow wave are mediated by nonlinear elastic characteristics of arterial walls. A nonlinear distributed model of human systemic arterial tree suitably determines the linear elastic properties of arterial walls. Different flow harmonics generates distinct pressure harmonics due to asymmetry of the arterial wall.

An assessment of methods for measurement of total arterial compliance to determine cardiac load has shown that the accuracy of methods relying on two-element windkessel (WK) model is better than for the three-element WK model. Accordingly, the two-area and pulse pressure methods are more accurate and have a greater applicability than the classic exponential decay and the diastolic area method. Methods using the three-element WK model are error-prone and tend to overestimate total arterial compliance.

Recent experimental studies have shown significant alterations of the vascular smooth muscle (VSM) tone when an artery is subjected to an elevation in pressure. Therefore, the VSM participates in the adaptation process not only by means of its synthetic activity (fibronectins and collagen) or proliferative activity (hypertrophy and hyperplasia) but also by adjusting its contractile properties and its tone level. In previous theoretical models describing the time evolution of the arterial wall adaptation in response to induced hypertension, the contribution of VSM tone has been neglected. In this study, we propose a new biomechanical model for the wall adaptation to induced hypertension, including changes in VSM tone. On the basis of Hill's model, total circumferential stress is separated into its passive and active components, the active part being the stress developed by the VSM. Adaptation rate equations describe the geometrical adaptation (wall thickening) and the adaptation of active stress (VSM tone). The evolution curves that are derived from the theoretical model fit well the experimental data describing the adaptation of the rat common carotid subjected to a step increase in pressure. This leads to the identification of the model parameters and time constants by characterizing the rapidity of the adaptation processes. The agreement between the results of this simple theoretical model and the experimental data suggests that the theoretical approach used here may appropriately account for the biomechanics underlying the arterial wall adaptation. arterial wall; remodeling; myogenic response; theoretical model; Hill's model; biomechanics

In this study, we investigated the stability and reactivation of preexisting Tonghua landslide deposits in China, including the adjacent stable slope. We used an integrated approach, combining a multichannel analysis of surface waves (MASW) and electrical resistivity tomography (ERT). We used ERT to determine groundwater seepage paths, weathering conditions, water content, and the depth to bedrock. High-resolution two-dimensional (2D) shear-wave velocity MASW images, on the other hand, played an essential role in detecting both horizontal and vertical compositions, disjointedness, and sliding surfaces related to lithological borders. Based on seismic models, we considered four geological layers encountered in the stable slope, including fractured (gravel) and weathered (phyllite) materials, as a sliding mass. We combined the 2D resistivity profiles obtained to create pseudo-three-dimensional ERT images to estimate water-saturated and unsaturated masses. From the tomography results, we identified different preexisting deposits, including buried arable clay deposits, old accumulated earthflow deposits, a water accumulation zone, and a fissure runoff. Based on the resistivity results, the bottom of the earthflow deposits is susceptible to water, and oversaturation can reactivate the earthflow.