Measurement of Arterial Geometry and Wall Composition in the Carotid Sinus Baroreceptor Area

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Abstract
The overall dimensions of the carotid sinus, the thicknesses of the individual layers within its wall, and the tissue composition of the tunica media were measured on histological sections of the carotid bifurcation fixed in vivo in anesthetized dogs, cats, and rabbits. The outstanding dimensional features of the carotid sinus as compared to the adjoining carotid segments are its thinned media-intima layer and increased ratio of internal radius to media-intima thickness. These differences carry a high level of significance statistically. There appears to be no marked increase in the ratio of radius to whole-wall thickness in the sinus portion of the carotid tree. The tunica media in the carotid sinus wall contains more than twice as much elastic tissue per unit volume (mean value 62.3% elastin) as the media in the carotid vessels adjoining the sinus; reciprocally, smooth muscle constitutes 16.4% of the tunica media in the sinus wall but approximately 50% or more of the media in the common, internal, and external carotid arteries caudal and cranial to the sinus (mean values in percent of total volume). Results are discussed in relation to the position of the baroreceptors within the sinus wall and mechanisms of stimulating them.