Model released. Pulmonary function in cystic fibrosis. A physiotherapist performing a lung function test on a patient using a Wright peak flow meter. This device measures the peak flow of air expired by the patient. The reading is compared with tables to establish the degree of obstruction in the bronchi. In front of the physiotherapist is a Vitalograph, which measures various aspects of lung function such as the vital capacity, forced vital capacity and forced expiratory rate. Cystic fibrosis is a hereditary disease affecting the exocrine glands. This may lead to thick mucus obstructing the bronchi with severe infections being a common complication.