Abstract
Despite considerable research efforts on the relationship between arterial geometry and cardiovascular pathology, information is lacking on the pulsatile geometrical variation caused by arterial distensibility and cardiomotility because of the lack of suitable in vivo experimental models and the methodological difficulties in examining the arterial dynamics. We aimed to investigate the feasibility of using a chick embryo system as an experimental model for basic research on the pulsatile variation of arterial geometry. Optical microscope video images of various arterial shapes in chick chorioallantoic circulation were recorded from different locations and different embryo samples. The high optical transparency of the chorioallantoic membrane (CAM) allowed clear observation of tiny vessels and their movements. Systolic and diastolic changes in arterial geometry were visualized by detecting the wall boundaries from binary images. Several to hundreds of microns of wall displacement variations were recognized during a pulsatile cycle. The spatial maps of the wall motion harmonics and magnitude ratio of harmonic components were obtained by analyzing the temporal brightness variation at each pixel in sequential grayscale images using spectral analysis techniques. The local variations in the spectral characteristics of the arterial wall motion were reflected well in the analysis results. In addition, mapping the phase angle of the fundamental frequency identified the regional variations in the wall motion directivity and phase shift. Regional variations in wall motion phase angle and fundamental-to-second harmonic ratio were remarkable near the bifurcation area. In summary, wall motion in various arterial geometry including straight, curved and bifurcated shapes was well observed in the CAM artery model, and their local and cyclic variations could be characterized by Fourier and wavelet transforms of the acquired video images. The CAM artery model with the spectral analysis method is a useful in vivo experimental model for studying pulsatile variation in arterial geometry.
Highlights
Arterial geometry is among the main determinants of local hemodynamic forces, which are closely related to cardiovascular pathophysiology [1]
We aimed to establish an in vivo experimental model suitable for investigating pulsatile variation of an arterial geometry
We investigated the feasibility of using chick chorioallantoic membrane (CAM) model as a source of an in vivo arterial system with various geometries
Summary
Arterial geometry is among the main determinants of local hemodynamic forces, which are closely related to cardiovascular pathophysiology [1]. Zarins et al [3] reported that the atherosclerotic plaques in the carotid artery preferentially develop at the posterior wall of the internal carotid artery because of the formation of flow recirculation zone associated with low WSS and high oscillatory shear index [9] Based on this finding, numerous studies have been conducted to clarify the hemodynamic-geometric causes of the inter- and intra-individual differences in carotid atherosclerosis, which is currently known to be associated with geometric parameters of the carotid bifurcation, such as the cross-sectional area or diameter ratio of the internal to common carotid arteries [4, 10]. Results of these studies indicate that arterial wall compliance does not significantly affect the global structure of the blood flow pattern, but significantly reduces the WSS magnitude These results suggest that compliant wall modeling, known as fluid-structure interaction (FSI) analysis, closely reflects physiological conditions; FSI analysis is necessary for in vivo estimation of the spatio-temporal distribution of local WSS [15]. FSI simulation has inherent limitations in analysis reliability because obtaining input information about the physical properties of arterial vessels and surrounding tissues is difficult and complicated by their inhomogeneity [16,17,18]
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