Tracheal extension in respiration.

Abstract

It has long been known that the lower end and bifurcation of the trachea are displaced downwards during inspiration. Macklin (1925) described a vertical respiratory displacement of 21 mm. a healthy young adult female. Bruckner (1952), a radiological study, demonstrated an inspiratory descent of the carina of about one thoracic vertebral body young adults of 19 to 25 years of age. Holden and Ardran (1957), a meticulous examination of bronchograms from subjects aged 12 to 65 years, concluded that in deep inspiration the trachea increased length up to one fifth and diameter by about one tenth. In a personal observation, on inspiration the carina descended 30 mm. a young adult male with a full inspiratory movement. Thus, young adults, the carina descends by about 1 in. (2.5 cm.) with deep inspiration, i.e., about 20% of the unextended length of the trachea. There are no references the literature to similar observations infants and young children whom the technical difficulty of securing a full inspiratory and expiratory movement for radiographic investigation is obvious. Also, most observers have examined only the movement of the carina and have not considered changes the whole length of the trachea. Keith (1909) drew attention to the fact that certain parts of the lung are expanded more readily than others. The bases and sterno-costal surfaces related to the more mobile parts of the thoracic wall expand more readily than the apices, mediastinal surfaces, and posterior margins, related to less mobile parts. These areas he described as areas of direct or of indirect expansion. The thoracic wall does not move uniformly during inspiration; the parts which move most are the diaphragmatic and sterno-costal surfaces. Thus the lung tends to expand a downward and forward direction. Now the lung root must obviously descend to facilitate this movement. In