The angle of arterial tapering increases with ageing, and the geometrical changes of the aorta may cause an increase in central arterial pressure and stiffness. The impact of tapering has been primarily studied using frequency‐domain transmission line theories. In this work, we revisit the problem of tapering and investigate its effect on blood pressure and pulse wave velocity (PWV) using a time‐domain analysis with a 1D computational model. First, tapering is modelled as a stepwise reduction in diameter and compared with results from a continuously tapered segment. Next, we studied wave reflections in a combination of stepwise diameter reduction of straight vessels and bifurcations, then repeated the experiments with decreasing the length to physiological values. As the model's segments became shorter in length, wave reflections and re‐reflections resulted in waves overlapping in time. We extended our work by examining the effect of increasing the tapering angle on blood pressure and wave intensity in physiological models: a model of the thoracic aorta and a model of upper thoracic and descending aorta connected to the iliac bifurcation. Vessels tapering inherently changed the ratio between the inlet and outlet cross‐sectional areas, increasing the vessel resistance and reducing the compliance compared with non‐tapered vessels. These variables influence peak and pulse pressure. In addition, it is well established that pulse wave velocity increases in an ageing arterial tree. This work provides confirmation that tapering induces reflections and offers an additional explanation to the observation of increased peak pressure and decreased diastolic pressure distally in the arterial tree.

Blood pressure carries crucial information about the response of the arterial system to the beating heart. Extracting useful information from the blood pressure plays a significant role in the diagnosis and treatment of cardiovascular disease such as hypertension. There are many studies focusing on the existence of reflection waves in the ascending aorta and their influence on the amplitude of pressure. However, there is an ongoing debate about their origin, and the distance that a reflection wave can travel. In this study, a one-dimensional (1D) model of a series of bifurcations was used to analyse the effect of bifurcations on the pressure amplitude. A comparison was made between the pressure in the inlet of the model and in the terminal ends. Results showed an exponential decay with increasing numbers of bifurcations with no reflections reaching the inlet after the 7th generation of bifurcations. Therefore, a single reflection originating at the periphery may not be discernible at the aortic root.

Background: Stiffened arteries represent a major cardiovascular risk. Aim: We describe a vendor independent software for the non-invasive determination of arterial stiffness using ultrasound images. Methods: We have developed an intensity-based semiautomatic software for determining the edges of the luminal arterial walls (M-mode) and blood velocity (PW Doppler) to extract diameter and velocity waveform from ultrasound images. The upstroke of the two waveforms is automatically determined as well as the fit of the initial linear portion of the ln(D)U-loop. Pulse wave velocity (PWV), which is proportional to the slope of ln(D)U-loop during early systole is calculated as a measure of arterial stiffness. The user can override and correct the automatically determined parameters if necessary. Results: A semi-automatic code was developed for tracing the luminal diameter and blood velocity in the human ascending aorta. D and U waveforms were extracted and used in ln(D)U-loops to calculate PWV. Conclusions: The software described here can be used to assess, local aortic stiffness non-invasively, by using ultrasound measurements/images of the diameter and velocity waveforms.

Background Wave reflections play a major role in changing the shape of the pressure waveform. Reflections measured at the aortic root (AR) are thought to be due to the tapering of the aorta [1] and multiple reflection sites, however, there is no consensus on the source of those reflected waves. This research aims to better understand the origin of the reflected waves observed in AR. Methods A 1D computational model of arterial wave propagation was used to study the reflections in an arterial network that consists of 37 segments of large arteries [2]. A pulse was inserted in 3 peripheral vessels (Figure 1) and followed as it travelled back towards AR. A pressure ratio (PR) was described as the ratio between the pressure at AR to the inlet pressure to allow for comparisons between the effect of various reflected sites. Results The pulse wave lost its magnitude travelling back towards the heart. The pulse inserted from the iliac artery could hardly be observed in AR (Figure 2), and only 1% of the waves’ magnitude could be detected. PR of the wave inserted at the carotid artery is approximately 18 times larger than those generated at the iliac artery; both measured in the ascending aorta. Conclusion Waves reflected from the carotid bifurcation and the cerebral circulation are more likely to be seen in AR in comparison to reflected sites such as renal and iliac arteries. Further work is warranted to establish the contribution of reflections generated from various sites along the arterial bed.

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