Transverse images of the human thoracic trachea during forced expiration.

The thoracic trachea and the proximal portion of the major bronchi were imaged in five normal volunteers during a forced expiration maneuver using a cine-computer-tomography system. Sixteen images of two contiguous slices were obtained in less than 1 is while expiratory flow was recorded at the mouth. The area of the thoracic trachea decreased rapidly as flow rate rose to its maximum and the wave of collapse propagated distally. The compressive narrowing of both the pars membranacea and the ventrolateral wall was asymmetric. A contact area appeared between the posterior and the left lateral walls. In one subject the trachea was imaged during the entire maneuver with a lower scan frequency. By 725 ms after the beginning of the forced expiration, the area had first decreased to 15% of its initial value and then reincreased to 46% of its initial value. It stayed constant for the remainder of the maneuver. The measured maximum air velocity was greater than the estimated local wave velocity.