Abstract

The development, significance and function of the human carotid sinus are not clearly understood. The arterial wall of carotid sinus is densely enervated and it contains baroreceptive neural terminals. It has been hypothesized that the dilation, which may involve all vessels of the carotid bifurcation, serves to support pressure sensing. Another hypothesis based on phenomenological observations presumes that the function of the sinus is to slow the blood flow and reduce the pulsatility in order to protect the brain (1). Yet another postulate states that the sinus is an ontogenetic or phylogenic residual. More recently, in vitro and computational models have been used to investigate carotid hemodynamics. Complex flow patterns have been found in the carotid sinus. These patterns have been implicated in the carotid bulb heterogeneity and subsequent development of atherosclerosis at this site.

However, long term development of this unique sinus morphology has not been investigated. It is of both fundamental and clinical interest to form an understanding of the hemodynamics and developmental forces that play a role in remodeling of the carotid bifurcation and maturation of the sinus. This understanding can lead to better prognostication and therapy of carotid disease.

Therefore, a study of the morphological development of the human carotid bulb was initiated. Carotid bulbs from various human developmental stages were evaluated to test the hypothesis that morphology of the sinus reflects an acclimated change in response to alterations in cerebral blood supply with aging. This acclimation attempts to diminish hydraulic losses in the carotid bifurcation through reduced flow disturbances. Under basal conditions, a high level of blood supply to the brain is maintained that consumes about 15% of cardiac output. Furthermore, it may protect the brain from highly pulsatile blood flow conditions and/or the sinus wall from high shear stress.

Initially, we analyzed the sinus morphology and the angle of the carotid bifurcation in four human developmental stages, namely newborn, pediatric, adolescent and adult patients (Groups I, II, III, and IV, respectively). The analysis was performed using biplane digital subtraction angiograms to characterize changes that occur as the brain matures.

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