Airway wall remodeling: Inflammation involves all portions of the bronchial tree. The combination of smooth muscle contraction, mural inflammatory thickening, and vascular congestion increases airflow resistance. A membranous bronchiole from the patient is illustrated below. Compare it (A) with a normal bronchiole below (C). The entire wall, including the epithelium, is infiltrated by inflammatory cells. In a study of airway dimensions in asthma, it was found that the areas of the outer wall (area outside the smooth muscle, arrow A in diagram B), inner wall (area between basement membrane and outer smooth muscle, arrow B in diagram B), smooth muscle, and blood vessels were all greater than those in control lungs for both bronchi and bronchioles [1,2].

A.

B. Diagram: The outer line marks the outer border of the smooth muscle layer. The inner line marks the epithelial basement membrane. The connective tissue (A) is the outer wall (adventitia) and the connective tissue (B) is the inner wall (subepithelial area).

C.

Histology of nocturnal asthma: This patient died of a sudden respiratory arrest at 4 am (70% of sudden deaths and 80% of respiratory arrests in asthma occur during hours of sleep). Persons with attacks of nocturnal asthma have a fall in FEV1 during the night, and this fall has been correlated with increased numbers of eosinophils in alveolar walls of transbronchial biopsies at 4 am compared to numbers at 4 pm. Endobronchial biopsies showed no changes between 4 am and 4 pm in those with nocturnal asthma, nor did endobronchial or transbronchial biopsies from asthmatic patients without nocturnal asthma [3,4]. In A above, note the involvement of alveolar walls by inflammatory cells.

References

1. Kuwano K, Bosken C, Paré P, Bai T, Wiggs B, Hogg J. Small airways dimensions in asthma and in chronic obstructive pulmonary disease. Am Rev Respir Dis 1993; 148:1220-1225.

2. Carroll N, Elliot J, Morton A, James A. The structure of large and small airways in nonfatal and fatal asthma. Am Rev Respir Dis 1993; 147:405-410.

3. Kraft M, Djukanovic R, Wilson S, Holgate S, Martin R. Alveolar tissue inflammation in asthma. Am J Respir Crit Care Med 1996; 154:1505-1510.

4. Martin R. Small airway and alveolar tissue changes in nocturnal asthma. Am J Respir Crit Care Med 1998; 157, S188-S190.

Clinical summary Image 5

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