Going with the flow: Arterial dynamics in horses studied

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Model results (with and without gravity) compared with the averaged flow waveforms of all investigated horses at various arterial locations. Graphic: Vera et al. https://doi.org/10.1371/journal.pone.0221425

Researchers have developed a computer model of arterial circulation in horses, and hope it will be used to explore the reasons behind the major blood vessel ruptures seen in equines.

Arterial ruptures can occur in horses during exercise, during birth (failure of the uterine artery) and after phenylephrine administration.

Lisse Vera and  Daimé Campos Arias and their colleagues noted that computer models are used for studying arterial hemodynamics in humans. They have helped to understand the normal and abnormal characteristics of arterial pressure and flow waveforms.

In the research, based at Belgium’s Ghent University the study team set out to develop their one-dimensional computer model for horses.

They noted that scientific literature provided only limited information on arterial hemodynamics in horses, which proved to be a major challenge to develop an equine one-dimensional model.

On top of that, there are large differences between aortic arch and arterial branching patterns in horses and humans.

They based their model on anatomical data of the core arterial tree (lengths, diameters and branching angles) collected from post mortems on horses euthanized for reasons unrelated to the study. They also collected ultrasonographic flow profiles from the common carotid artery, external iliac artery, median artery and aorta in live horses.

Further, they collected data on pressure from the carotid artery and aorta for incorporation in the model.

The information was input into a previously validated 1D arterial network model in humans – in effect, developing the equine equivalent.

Data on terminal resistance and arterial compliance parameters were tuned to equine physiology, and friction coefficients were calculated and employed in the modelling.

The outcomes showed plausible predictions of pressure and flow waveforms throughout the central arterial tree in horses.

The researchers, who reported their findings in the open-access journal PLOS ONE, said consideration of gravity further improved model-based predicted waveforms.

“The model,” they said, “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.

“This model might contribute to a better understanding of some clinical findings, such as the origin of the more oscillatory flow patterns in horses, the higher prevalence of aortic rupture in Friesians compared to Warmblood horses, the occurrence of sudden death during exercise due to arterial rupture, the higher chance on uterine artery rupture in older mares, or the higher chance of arterial rupture after phenylephrine administration in older horses.”

Discussing their work, the researchers said that tuning the model parameters was based on plausible assumptions and scaling factors between human and equine patients. Further fine-tuning of the input parameters to equine physiology will be necessary to obtain a closer match with flow profiles in horses.

“Branching patterns and arterial dimensions can vary significantly between individual horses. Other important parameters, influencing flow velocity and pressure waves morphology are arterial elasticity and peripheral resistance.

“Equine arterial elasticity and peripheral vascular resistance are interesting criteria to further unravel in the future.”

During intensive exercise, the heart rate of horses may rise up to eight times above the resting rate and total aerobic capacity can reach a 40-fold increase, which is much greater compared to human athletes.

“By altering input parameters of the horse-specific model, this model might predict local pressures and flow profiles during these extreme circumstances and contribute to the understanding of the relatively high incidence of sudden death during exercise due to arterial rupture.

“As increasing age increases the risk of arterial disorders, it might also be interesting to use the present model to study the effect of age on arterial hemodynamics.

“Moreover the development and adjustment of this kind of computer model could lead to a better understanding of some intensively studied, but poorly understood clinical situations such as exercise-induced pulmonary hemorrhage.”

They said that, despite its generic character and limitations, outcomes from the model showed plausible predictions of pressure and flow waveforms throughout the portion of the arterial tree that was modeled.

The full study team comprised Vera, Campos Arias, Sofie Muylle, Patrick Segers and Gunther van Loon, all with Ghent University; and Nikos Stergiopulos, with the Laboratory of Hemodynamics and Cardiovascular Technology at EPFL in Lausanne, Switzerland.

Vera L, Campos Arias D, Muylle S, Stergiopulos N, Segers P, van Loon G (2019) 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. PLoS ONE 14(8): e0221425. https://doi.org/10.1371/journal.pone.0221425

The study, published under a Creative Commons License, can be read here.

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