Restoration of normal blood flow in atherosclerotic arteries promotes plaque stabilization

Focal comparison of experimental and finite element derived strain fields in a 3D IVUS-based computational model of vascular tissue under loading

Arterial tissues are subjected to mechanical loads that influence biological mechanisms in health and disease. Motivated by these observations, computational models to predict the vascular mechanical environment are increasingly being developed and applied. However, few computational vascular biomechanics studies are evaluated for accuracy. This study aimed to compare the transmural strain fields in healthy vascular tissue under physiologic loading between 3D intravascular ultrasound (IVUS)-based finite element (FE) models and image-based experimental measurements. IVUS image data were captured along a ∼ 15 mm segment in porcine carotid arteries (n = 3) in the reference configuration (∼10 mmHg) and at five axial positions under varied pressure loads. FE models were constructed from the full-length segment IVUS data, and model-predicted strains were determined using reported soft and stiff material properties for porcine tissue. Experimental strains were determined at each axial slice across the applied loads using a deformable image registration technique (Hyperelastic Warping). Both FE-predicted and experimental deformations exhibited non-linear behavior under loading, as observed in the material response curves. Following Warping parameter selection, results demonstrated that FE-predicted transmural strains with soft and stiff material properties bounded the experimentally-derived data at systolic pressures; however, sample variability was observed. At systolic pressure, Warping-derived and FE-predicted transmural strains showed good agreement, as RMSE values were < 0.09 and differences < 0.08. In conclusion, this study presents an experimental framework to assess accuracy in IVUS-based FE models, and results indicate that the computational framework can predict realistic deformations of arterial tissue; however, the accuracy strongly depends on tissue-specific material properties.

Ultrasound Induces Similar Temporal Endothelial Expression Patterns of eNOS and KLF2 as Normal Flow

OBJECTIVE

To determine the sensitivity of vascular endothelial cells to long durations of low-intensity pulsed ultrasound (LIPUS) compared to normal flow and identify the duration that maximizes expression of two mechanosensitive genes related to healthy endothelial function, endothelial nitric oxide synthase (eNOS) and Krüppel-like factor 2 (KLF2).

METHODS

Custom ultrasound exposure tanks were developed and the acoustic field was characterized. Human umbilical vein endothelial cells were seeded into culture plates and exposed to LIPUS at a frequency of 1 MHz and acoustic pressure of 217 kPa for 20 min, 1 h, 6 h, 9 h, or 24 h. As a comparator, other cells were exposed to normal flow. RT-qPCR was used to assess mRNA expression of eNOS and KLF2.

RESULTS

Maximum eNOS and KLF2 expression occurred at 6 h and was localized to the beam path. Both genes exhibited qualitatively similar patterns of expression under LIPUS compared to normal flow. LIPUS induced a more rapid beneficial response compared to normal flow, but flow induced higher expression of both genes. eNOS expression after 6 h of LIPUS was dependent on RNA yield and culture duration prior to experiments.

CONCLUSION

Endothelial cells exposed to longer durations of LIPUS than typically employed exhibited greater expression of beneficial genes. The temporal gene expression patterns resulting from LIPUS and normal flow suggest activation of similar signaling pathways. However, LIPUS also caused increased RNA yield that may be linked to proliferation, which would suggest more of a wound healing than atheroprotective phenotype.

Vascular remodelling in cardiovascular diseases: hypertension, oxidation, and inflammation

Optimal vascular structure and function are essential for maintaining the physiological functions of the cardiovascular system. Vascular remodelling involves changes in vessel structure, including its size, shape, cellular and molecular composition. These changes result from multiple risk factors and may be compensatory adaptations to sustain blood vessel function. They occur in diverse cardiovascular pathologies, from hypertension to heart failure and atherosclerosis. Dynamic changes in the endothelium, fibroblasts, smooth muscle cells, pericytes or other vascular wall cells underlie remodelling. In addition, immune cells, including macrophages and lymphocytes, may infiltrate vessels and initiate inflammatory signalling. They contribute to a dynamic interplay between cell proliferation, apoptosis, migration, inflammation, and extracellular matrix reorganisation, all critical mechanisms of vascular remodelling. Molecular pathways underlying these processes include growth factors (e.g., vascular endothelial growth factor and platelet-derived growth factor), inflammatory cytokines (e.g., interleukin-1β and tumour necrosis factor-α), reactive oxygen species, and signalling pathways, such as Rho/ROCK, MAPK, and TGF-β/Smad, related to nitric oxide and superoxide biology. MicroRNAs and long noncoding RNAs are crucial epigenetic regulators of gene expression in vascular remodelling. We evaluate these pathways for potential therapeutic targeting from a clinical translational perspective. In summary, vascular remodelling, a coordinated modification of vascular structure and function, is crucial in cardiovascular disease pathology.