[Bronchial caliber study: a continuous challenge in pneumology]

The caliber and the bronchial wall represent the anatomical substratum of several diseases of the respiratory tract. Many investigations allow qualitative and quantitative approaches but none can appreciate exactly the injuries degree and the lesions extent. The radiological methods are powerful in particular the high resolution computed tomography with great in-depth descriptive capacity. The respiratory functional tests with a variable sensitivity allow a dynamic but indirect analysis, the provocation test studies bronchial hyperresponsiveness and the plethysmography measures the airways specific resistance. The bronchoscopy explores the bronchi directly but is confronted with the problem of the image distortion. The fields of studies of the bronchial gauge are vast including all bronchopulmonary pathology and the correlation of two different methods allows a better evaluation.