Optimised Design of An Arterial Network Model Reproduces Characteristic Central and Peripheral Hemodynamic Waveform Features in Young Adults

Abstract

The arterial network in healthy young adults is thought to be structured to minimise wave reflection in conduit arteries, producing an ascending aortic pressure waveform with three key features: early systolic peak, negative systolic augmentation, and diastolic hump. One-dimensional computer models have provided significant insights into arterial haemodynamics, but no previous models of the young adult have exhibited these three features. Since the latter was likely to be related to unrepresentative or non-optimised impedance properties of the model arterial networks, we developed a new ‘YoungAdult’ model that incorporated 1) a novel and more accurate empirical equation for approximating wave speeds, based on area and relative distance to elastic-muscular arterial transition points, 2) optimally-matched arterial junctions, and 3) an improved arterial network geometry that eliminated ‘within-segment’ taper (which causes wave reflection in conduit arteries) whilst establishing ‘impedance-preserving’ taper. These model properties led to wave reflection occurring predominantly at distal vascular beds, rather than in conduit arteries. The model predicted all three typical characteristics of an ascending aortic pressure waveform observed in young adults. When compared with non-invasively acquired pressure and velocity measurements (obtained via tonometry and Doppler ultrasound in 7 young adults), the model was also shown to reproduce the typical waveform morphology observed in the radial, brachial, carotid, temporal, femoral, and tibial arteries. The YoungAdult model provides support for the concept that the arterial tree impedance in healthy young adults is exquisitely optimised, and it provides an important baseline model for investigating cardiovascular changes in ageing and disease states.

Novel Centroid Method for Robust Evaluation of Return Time of Reflected Waves in the Systemic Arterial Network

“…To assess the accuracy of these methods using a GTRT, every individual backward wave arriving at the ventricle must be tracked; this can only be achieved through computational methods. We recently developed and validated a non-linear one-dimensional model of the systemic arterial circulation of a young adult-the 'YoungAdult' model-the details of which are described elsewhere (27). In brief, a two-chamber heart model served as the input to the systemic arterial circulation, and distal arteries were terminated with 3-element windkessels representing vascular beds.…”

Reflections on reflected waves in ‘YoungAdult’

“…Therefore, all bifurcations and junctions in the large arteries were carefully matched through to a mismatched interface between terminal arteries and their downstream vascular beds. This assumption may have contributed to the model limitations, such as lack of the typical pressure amplification in the limbs that has been demonstrated previously by many investigators and confirmed by Kondiboyina et al., 2022 in their small validation sample (Kondiboyina et al., 2022). For example, their Table 2 shows that model systolic and pulse pressures fall between brachial and radial and between femoral and posterior tibial arteries whereas corresponding values increase in the validation sample.…”

“…Innovations incorporated by Kondiboyina et al, 2022 into the 'YoungAdult' model are commendable and will advance the field. However, assumptions enforced when initializing the model require thought and Perspective J Physiol 600.20 must reflect key empirical observations, such as pressure amplification.…”

“…To bridge this gap, modelling studies are often employed to manipulate individual elements of load and assess the effects on observed pressure and flow. In the current issue of The Journal of Physiology , Kondiboyina et al., 2022 have introduced a sophisticated new ‘YoungAdult’ model of the arterial system that adds to the toolbox available to investigators working in the field (Kondiboyina et al., 2022). The goals of the study were to derive a model that reproduces the characteristics of a youthful central arterial pressure waveform: an early peak with negative pressure augmentation (type C waveform) and a diastolic pressure hump.…”

“…This potential adverse effect of wave reflection needs to be balanced against demonstrated adverse effects of aortic stiffening, impedance‐matching and reduced global wave reflection on microvascular structure and function. Kondiboyina et al., 2022 are correct to cite the ‘beautiful tuning’ of an arterial system that juxtaposes a low‐impedance transmission line with high‐impedance branch vessels; however, additional reflection on the roles of wave reflection may be necessary to fully realize the potential of the model.…”