Section: Information In-depth
Chronic bronchitis refers to a persistent inflammatory change in the bronchial tree that may involve lobar bronchi or the smaller airways. Chronic bronchial inflammation or irritation, regardless of cause, seems to promote the predictable responses of increased tracheobronchial secretions, cough and progressive architectural changes in the bronchial tree, which alter airflow.
Small airway obstruction, often with mucus, leads to an increased work of breathing, which can be compounded by dynamic, expiratory collapse of the large airways (the large airways close or collapse when breathing out). Lobar bronchi and the intrathoracic trachea may totally collapse during forced expiration or with coughing. Mucus and bronchial secretions stimulate a cough.
Mucus plugs may further obstruct air flow and airway collapse. These changes can predispose the cat to recurrent respiratory infections. These changes cause nonreversible and often result in progressive changes.
Visual examination of the bronchial tree, for example by fiberoptic bronchoscopy, demonstrates red and granular mucosa (lining), mucus hypersecretion and discharge that may occlude smaller bronchi. Bronchiectasis, pneumonia, chronic bronchitis and large airway disease are evident in some cats.
Causes of bronchitis are frequently not determined but may include chronic or recurrent viral or bacterial infection that may suggest an abnormality of local immunity, lingering infection, ciliary dyskinesis, which is a congenital abnormality of respiratory cilia which is rare, and environmental pollutants, including passive exposure to cigarette smoke and hypersensitivity reactions.
Environmental pollutants are speculated to be causes of chronic airway irritation and injury and there may be a relationship of chronic respiratory diseases to poor oral health, but this is unproven.
Other medical problems can lead to symptoms similar to those encountered in chronic bronchitis. Diagnostic testing such as radiographs (X-rays) and bronchoalveolar lavage (BAL]) will often diagnose chronic bronchitis. Further diagnostic testing may be needed to determine secondary factors such as active inflammation or to eliminate other causes of similar symptoms such as heart disease.
Diseases that can appear similar to those with chronic bronchitis include:
Aspiration (the act of inhaling) from chronic esophageal disease
Bronchopneumonia (bacterial or fungal)
Congestive heart failure
Foreign body
Heartworm disease
Inflammatory lung disease
Lung worm infection
Pneumonia (inflammation/infection of the lungs)
Pulmonary fibrosis (formation of fibrous tissue in the lungs)
Pulmonary neoplasia (lung tumors)
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