Respiratory tract bronchioles

Other disorders of the lower respiratory tract include emphysema (lung disorder in which the terminal bronchioles or alveoli become enlarged and plugged with mucus) and chronic bronchitis (chronic inflammation and possibly infection of die bronchi). Chronic obstructive pulmonary disease (COPD) is die name given collectively to emphysema and chronic bronchitis because die obstruction to die airflow is present most of the time. Asdima diat is persistent and present for most of die time may also be referred to as COPD. 

Lower respiratory tract infections include infectious processes of the lungs and bronchi, pneumonia, bronchitis, bronchiolitis, and lung abscess. 

Bronchiolitis is an acute viral infection of the lower respiratory tract of infants that affects approximately 50% of children during the first year of life and 100% by 3 years. 

The most common clinical signs of bronchiolitis are found in Table 43-4. A prodrome suggesting an upper respiratory tract infection, usually lasting from 2 to 8 days, precedes the onset of clinical symptoms. 

The sites of action and effects of ozone and other photochemical oxidants are described in Chapters 8 and 9. Recent work with primates has suggested that ozone is absorbed along the entire respiratory tract, penetrates more into the peripheral nonciliated airways, and causes more lesions in the respiratory bronchioles and alveolar ducts as the inhaled ozone concentration increases from 0.2 to 0.8 ppm. The most common and most severe tissue damage was observed in the respiratory bronchioles. The ciliated cells in the terminal bronchioles and the Type 1 cells in the epithelial layer of the proximal alveoli of rats were the... 

After acute mild insult the nonciliated cells proliferate and the epithelium regenerates to normal. In the airways, nonciliated basal cells are the main proliferating population. In the bronchioles, the Clara cell is the main precursor cell for regeneration. Because of the delicate nature of the respiratory tract epithelium and the close proximity of subepithelial blood vessels, an inflammatory response occurs to all but the mildest form of injury. Many lesions are therefore diagnosed as rhinitis, tracheitis, and bronchiolitis and qualified as acute, subacute, and chronic depending on the stage of the response. 

Rats exposed to 500 ppm 6 hours daily for 5 days exhibited marked eye and nasal irritation, and a number of animals had corneal opacity by the end of the third day the mortality rate was 20%, and at autopsy, findings were acute purulent bronchiolitis and bronchopneumonia. Exposure to 25 ppm for 14 days caused respiratory tract epithelial hyperplasia, squamous metaplasia, and clinical rales. ... 

Inhaled particles of 20 [im diameter or more tend to be retained in upper parts of the respiratory tract (trachea, pulmonary bronchi and terminal bronchioles) and then removed by ciliary action. In contrast, smaller particles of around 6 pm diameter reach all parts of the respiratory system including the alveolar sacs. Smaller (2 pm) and very small particles (0.2 pm) may not reach the alveolar sacs, only the terminal bronchioles and alveolar ducts. Particles of diameter 1 pm or less may be absorbed if they reach the alveolar sacs. 

Respiratory syncytial virus (RSV) infection is a major cause of bronchiolitis in infants, whereas influenza A infection usually manifests as an upper respiratory tract infection. The immunological responses of infants to RSV infection and influenza A infection are different. In our studies of the cytokine responses during these infections, we found that the serum concentrations of IL-4, IL-5, RANTES, and soluble intercellular adhesion molecule-1 (sICAM-1) in infants with RSV infection were significantly higher than those with influenza A infection (S8). The concentration of TNF-a in nasopharyngeal aspirates was significantly lower in infants with RSV infection. Therefore, a predominant T helper cell type 2 (Th2) cytokine and related immunological response was observed in infants with RSV infection, whereas a predominantly proinflammatory cytokine response was observed in infants with influenza A infection. This may explain the different clinical manifestations of the two viral infections in infants (S8). 

The evaporation of liquid ammonia in contact with flesh can cause frostbite. Ammonia is a potent skin corrosive and can damage eye tissue. When inhaled, ammonia causes constriction of the bronchioles. Because of its high water solubility, ammonia is absorbed by the moist tissues of the upper respiratory tract. Irritant damage to the lungs from ammonia can cause edema and changes in lung permeability. 

Pulse rate declined initially, but doubled over the normal rate after 10 h. Animals that died had pulmonary edema. Other clinical effects included ocular irritation, sneezing, salivation, retching, vomiting, general excitement, dyspnea, respiratory distress. Pathologic examination revealed necrosis of the epithelial lining of the respiratory tract, pneumonia, bronchitis, bronchiolitis, and fibrosis. 

Respiratory Tract Infections, Lower CHAPTER 43 I Clinical Presentation of Bronchiolitis I... 

---