1. Cytologic examination of sputum after an asthmatic attack shows eosinophils, Charcot-Leyden crystals (orange, elongated, rhomboid crystals formed by degranulation of eosinophils) and Curshmann's spirals (dark staining core surrounded by lighter mucous). Biopsy is rarely done. In patients dying of status asthmatics the lungs are over-expanded and small airways are occluded by mucoid secretions. There is a variable amount of bronchiolar inflammation including eosinophilic infiltrates. Mucus glands are hyperplastic with hyperplasia of bronchial and bronchiolar smooth muscle.

This is defined as abnormal, permanent enlargement of air spaces distal to the terminal bronchioles, due to destruction of aveolar walls and without fibrosis. It is classified as follows:

1. Centriacinar emphysema involves primarily the respiratory bronchioles and is the most common type. It is the type seen in cigarette smokers.
2. Panacinar emphysema involves the entire acinus. It is one-twentieth as common as centricular emphysema. It is the type seen in alpha 1 - antitrypsin deficiency.
3. Paraseptal emphysema involves the distal part of the lobule. Extensive involvement of the lung is rare. Some cases of spontaneous pneumothorax may be due to this type of emphysema.
4. Irregular emphysema is associated with scarring and has no particular relationship to the acinus.
5. Bullous emphysema, by definition, is composed of lesions greater than 1 cm. in diameter, and can be associated with any type of emphysema.
6. A bleb is a localized pocket of interstitial emphysema, typically subpleural, with no destruction of lung tissue.

The histologic features are chronic inflammation (usually lymphocytic) of bronchi with hyperplasia of goblet cells and mucus glands. The Reid index measures the gland to wall ratio (normally glands are one-third of wall thickness as measured from epithelial basement membrane to cartilage).

The airways are abnormally and permanently dilated with variable amounts of mucus and inflammation. Superimposed infection may be present e.g., aspergillosis.

1. In cystic fibrosis the changes are diffuse often with green yellow mucoid impaction.
2. In Kartagener's syndrome, lack of dienin arms in cilia can be seen by electron microscopy.
3. Post-infectious bronchiectasis may be localized or diffuse depending on location and extent of primary disease.

1. This is a fibrosing disease of small airways which are defined as less than 2 mm. in diameter. There is luminal obstruction by inflammatory and fibrotic changes.