[Differential diagnosis of stenoses of the large airways by means of lung function tests (author's transl)].

The different pathophysiological mechanisms involved in producing airflow obstruction at different sites in the tracheobronchial tree enable their differentiation by means of pulmonary function tests. These tests include volume-time measurements at forced in- and expiration, flow-volume measurements forced in- and expiration and flow-pressure measurements in the bodyplethysmograph during quiet breathing. In 23 patients with localized stenosis of the central tracheobronchial tree (12 with extra-thoracic tracheal stenosis, 4 with intrathoracic tracheal stenosis and 7 with main bronchus stenosis) the following parameters proved to be of diagnostic value: In the differential diagnosis of intra-extra-thoracic tracheal stenosis the forced in-expiratory flow-volume curve, in main bronchus stenosis the plethysmographically obtained flow-pressure curve with a large phase lag at zero flow ("trapped air"). In extreme cases the qualitative analysis of the spirogram in connection with the static lung volumes can be diagnostic.