In Vivo Roentgenographic Examination of Parasympathetic Innervation of Small Airways

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Abstract
A study was made roentgenographically of the peripheral airways in vivo by using powdered tantalum as contrast medium, a small focal spot x-ray tube (0.06 mm side dimensions), and primary radiographic magnification. Despite the limited output of the x-ray tube (2.5 ma), we obtained satisfactory bronchograms with short exposures at 120 kVp. This technique enabled us to study the effect of vagal stimulation on the airways in vagotomized cats and dogs. Vagal stimulation resulted in slight constriction in the trachea and large bronchi and maximum constriction in airways whose resting diameters were 1–5 mm in dogs and 0.8–2.0 mm in cats. Constriction was diminished in airways with diameters less than 0.8–1.0 mm and was insignificant in airways less than 0.5 mm in diameter. In a comparative study with x-ray tubes of different focal spot side dimensions, we established that the tube with a 0.06 mm focal spot increased the ability of observers to detect changes in airway diameter.

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