Hemodynamic Changes in the Carotid Artery after Infusion of Normal Saline Using Computational Fluid Dynamics

Abstract

Purpose: To study the effect of the infusion of normal saline on hemodynamic changes in healthy volunteers using computational fluid dynamics (CFD) simulation. Methods: Eight healthy subjects participated and 16 carotid arteries were used for the CFD analysis. A one-liter intravenous infusion of normal saline was applied to the participants to observe the hemodynamic variations. Blood viscosity was measured before and after the injection of normal saline to apply the blood properties on the CFD modeling. Blood viscosity, shear rate, and wall shear stress were visually and quantitatively shown for the comparison between before and after the infusion of normal saline. Statistical analyses were performed to confirm the difference between the before and after groups. Results: After the infusion of normal saline, decreased blood viscosity was observed in the whole carotid artery. At the internal carotid artery, the recirculation zone with low intensity was found after the injection of normal saline. Increased shear rate and reduced wall shear stress was observed at the carotid bifurcation and internal carotid artery. The hemodynamic differences between before and after groups were statistically significant. Conclusions: The infusion of normal saline affected not only the overall changes of blood flow in the carotid artery but also the decrease of blood viscosity.

Localized Elevation of Wall Shear Stress Is Linked to Recent Symptoms in Patients with Carotid Stenosis

“…We imported unstructured spatial tetrahedral mesh files into a FLUENT model with ANSYS software and set the following boundary conditions: (1) vascular wall characteristics – vascular walls were set to smooth, no penetration of rigid [20]; (2) blood properties – blood was assumed to be a laminar and incompressible Newtonian fluid with a density of 1,050 kg/m 3 and a viscosity of 0.0035 Pa∙s [21, 22]; (3) considering that parabolic velocity profiles have been used in more than half of the previous CFD studies and have yielded relatively similar results to patient-specific velocity profiles, we used the instantaneous velocity profile of the common carotid artery in healthy patients as the inlet velocity boundary [23, 24], and the outlet boundary condition is set to free outflow [20, 25, 26]; (4) to avoid initial influences, each model was simulated for three cardiac cycles, and the third cycle’s outcomes (1.61–2.40 s) were used [27] (shown in Fig. 2).…”

A Comparison of Newtonian and Non-Newtonian Models for Simulating Stenosis Development at the Bifurcation of the Carotid Artery

“…The pulse shape was derived from 3560 cardiac cycles of Doppler ultrasound measurements taken from six female and eleven male volunteers who had no symptoms or diagnosis of cardiovascular disease and so can be assumed to be normal human subjects [56]. It has been applied in a range of simulations of the carotid artery [57][58][59][60][61]. This was implemented at the base of the geometry where the distribution functions are set to their equilibrium values, Equation (4), for the time-dependant normal velocities shown in Figure 1.…”

The Rheology of the Carotid Sinus: A Path Toward Bioinspired Intervention

“…For example, when reconstituting blood volume lost during surgery, consideration for blood viscosity (itself a main component of the shear properties of blood)-in addition to volume and oxygen deliverymay facilitate improved outcomes and more cost-effective administration. Further supporting the sinus region's possible suitability in this regard, Lee et al (2020) performed a very elegant study in which they studied changing flow patterns that result from blood viscosity after a bolus of crystalloid. To eight healthy subject they administered a one-liter bolus of normal saline.…”

“…The types of forces that act on vascular endothelium are broadly thought of as WSS or circumferential stretch ( Lu and Kassab, 2011 ). Whereas circumferential stretch reflects blood pressure, WSS depends on fluid properties and flow conditions, and it is highly affected by viscosity ( Lee et al, 2020 ). Therefore, the unique presence of such stress fields suggests that transduction at the sinus may be biased toward shear stress as it carries more information on the overall hemodynamics than just pulsatile pressure.…”