Changes in the area of the larynx, the airways and the lungs can lead to performance impairment. Through the nasal passage and the opened larynx, the video endoscope is passed into the trachea and allows the examiner to investigate the airway all the way down to where it branches into the two bronchi. Samples of secretions (tracheobronchial secretion) can be collected for examination. Degree of mucous congestion (amount and viscosity of secretion) and changes of the mucous membrane of the lower airways can also be assessed. In horses, coughing, nasal discharge, unusual respiratory noises or poor performance are indications for tracheoscopy, bronchoscopy and/or laryngoscopy.