Tracheal size and shape: effects of change in intraluminal pressure.

We used CT to examine the tracheas of two healthy adults at functional residual capacity, first at an intratracheal pressure of +20-cm H2O and then at -20-cm H2O. In the intrathoracic portions of the tracheas there was little change in cross-sectional area between the two pressures. However, in the neck the cross-sectional areas decreased by about one third from the higher pressure to the lower. The membranous posterior wall of the woman's extrathoracic trachea bulged backwards strikingly at the higher pressure but was drawn well into the tracheal lumen at the lower pressure. The two tracheas were 6% and 12% shorter at the lower pressure, and the intratracheal volume was 17% to 23% less. The data show that the size and shape of the extrathoracic portion of the normal adult trachea are very responsive to moderate changes in intraluminal pressure.