[Tracheal dimensions in young twins].

Tracheal dimensions were analyzed radiographically in 17 pairs of healthy high school boys (12 pairs of monozygotic twins and 5 pairs of dizygotic twins). Coefficients of variation in interindividual extra- and intrathoracic tracheal widths, tracheal depth, tracheal length, and cross sectional area ranged from 9.6 to 17.3%. Genetic influence was found in intrathoracic as well as extrathoracic tracheal widths at maximal expiration and in extrathoracic tracheal width at maximal inspiration. Intrathoracic tracheal width remained the same at either maximal inspiration or expiration. However, extrathoracic tracheal width became larger at maximal inspiration regardless of great changes in pleural pressure. These results indicate that tracheal rings may be influenced by genetic factors and that extrathoracic width may be enlarged during maximal inspiration.