Novel insights into the elastic and muscular components of the human trachea.

Despite its probable importance in health and disease, the elastic tissue in the trachea has rarely been investigated. In addition, various aspects of the trachealis muscle are controversial. The aim of this study was to clarify this clinically relevant anatomy. Ten cadaveric tracheobronchial specimens (age range 68-101 years; seven males; no major airway pathology) were qualitatively investigated by microdissection. Serial histologic sections from multiple sites in three specimens were analyzed after staining for elastin. Findings were correlated with observations from video tracheobronchoscopies. An extensive and prominent meshwork of elastic tissue was found within the trachea and bronchi. Elastic fibers were predominantly longitudinal and aggregated into discrete bundles within the membranous wall of the trachea and main bronchi; a discrete fibroelastic membrane bridging the membranous wall of the trachea; and vertical laminae connecting the ends of successive cartilages. The longitudinal elastic bundles continued into the segmental bronchi, becoming thinner and more circumferentially distributed. Trachealis consisted of a transverse layer of smooth muscle deep to the fibroelastic membrane of the membranous wall of the trachea, together with scattered longitudinal muscle bundles, mostly embedded within the fibroelastic membrane in the distal half of the trachea. In conclusion, there is an extensive but relatively neglected elastic framework within the tracheobronchial tree. This is likely to have major clinical relevance to the pathophysiology of respiratory disease and ageing. The trachealis muscle is more complex than previously stated.

In vivo and in vitro morphometry of the human trachea.

Most morphometric studies of the human trachea have relied on plain radiographs with their attendant limitations. Reports using computed tomography (CT) have focused on the growing trachea or one particular dimension. The aim of this study was to document the morphometry of the adult trachea in vivo using high-resolution chest CT scans, supplemented by data from cadavers. Sixty anonymised high-resolution chest CT scans (aged 22-88 years, 40 males) were analyzed. Scans were performed using a standardized breath-holding technique in patients with no distorting intrathoracic pathology. Standardized tracheal measurements included: length, maximum antero-posterior and transverse diameters, volume, subcarinal angle, and carinal position in relation to the tracheal midline. Measurements were also made in 10 cadaver tracheas (aged 68-101 years, 7 males). CT data showed that mean tracheal length (males 105.1 +/- 9.8 mm, females 98.3 +/- 8.7 mm), maximum antero-posterior and transverse diameters, and tracheal volume (males 35.6 +/- 6.8 cm3, females 24.7 +/- 6.1 cm3) were all significantly greater in men (P < or = 0.01). The subcarinal angle was very variable (mean 78 +/- 20 degrees , range 36-121 degrees ) and showed no correlation with age or gender. The carina was sited to the left of the tracheal midline in 49 (81%) patients. Cadaver tracheas had 14-19 tracheal rings and the posterior membranous trachea was wider in men (17.7 +/- 4.4 mm vs. 11.8 +/- 3.0 mm, P = 0.07). In conclusion, there is marked sexual dimorphism in the morphometry of the human trachea. The variation in adult tracheal dimensions in vivo is greater than in standard descriptions. These data may be valuable when interpreting chest CT scans and when calculating respiratory dead space.