Pathophysiology
Acute bronchitis leads to the hacking cough and phlegm production that often follows upper respiratory tract infection. This occurs because of the inflammatory response of the mucous membranes within the lungs' bronchial passages. Viruses, acting alone or together, account for most of these infections.[2, 3]
In children, chronic bronchitis follows either an endogenous response (eg, excessive viral-induced inflammation) to acute airway injury or continuous exposure to certain noxious environmental agents (eg, allergens or irritants). An airway that undergoes such an insult responds quickly with bronchospasm and cough, followed by inflammation, edema, and mucus production. This helps explain the fact that apparent chronic bronchitis in children is often actually asthma.
Mucociliary clearance is an important primary innate defense mechanism that protects the lungs from the harmful effects of inhaled pollutants, allergens, and pathogens.[4] Mucociliary dysfunction is a common feature of chronic airway diseases.
The mucociliary apparatus consists of 3 functional compartments: the cilia, a protective mucus layer, and an airway surface liquid (ASL) layer, which work together to remove inhaled particles from the lung. Animal study data have identified a critical role for ASL dehydration in the pathogenesis of mucociliary dysfunction and chronic airway disease.[5] ASL depletion resulted in reduced mucus clearance and histologic signs of chronic airway disease, including mucous obstruction, goblet cell hyperplasia, and chronic inflammatory cell infiltration. Study animals experienced reduced bacterial clearance and high pulmonary mortality as a result.
The role of irritant exposure, particularly cigarette smoke and airborne particulates, in recurrent (wheezy) bronchitis and asthma is becoming clearer. Kreindler et al demonstrated that the ion transport phenotype of normal human bronchial epithelial cells exposed to cigarette smoke extract is similar to that of cystic fibrosis epithelia, in which sodium is absorbed out of proportion to chloride secretion in the setting of increased mucus production.[6] These findings suggest that the negative effects of cigarette smoke on mucociliary clearance may be mediated through alterations in ion transport.
McConnell et al noted that organic carbon and nitrogen dioxide airborne particulates were associated with the chronic symptoms of bronchitis among children with asthma in southern California.[7]
A chronic or recurrent insult to the airway epithelium, such as recurrent aspiration or repeated viral infection, may contribute to chronic bronchitis in childhood. Following damage to the airway lining, chronic infection with commonly isolated airway organisms may occur. The most common bacterial pathogen that causes lower respiratory tract infections in children of all age groups is Streptococcus pneumoniae. Nontypeable Haemophilus influenzae and Moraxella catarrhalis may be significant pathogens in preschoolers (age < 5 y), whereas Mycoplasma pneumoniae may be significant in school-aged children (ages 6-18 y).
Children with tracheostomies are often colonized with an array of flora, including alpha-hemolytic streptococci and gamma-hemolytic streptococci. With acute exacerbations of tracheobronchitis in these patients, pathogenic flora may include Pseudomonas aeruginosa and Staphylococcus aureus (including methicillin-resistant strains), among other pathogens. Children predisposed to oropharyngeal aspiration, particularly those with compromised protective airway mechanisms, may become infected with oral anaerobic strains of streptococci.
PathophysiologyAcute bronchitis leads to the hacking cough and phlegm production that often follows upper respiratory tract infection. This occurs because of the inflammatory response of the mucous membranes within the lungs' bronchial passages. Viruses, acting alone or together, account for most of these infections.[2, 3] In children, chronic bronchitis follows either an endogenous response (eg, excessive viral-induced inflammation) to acute airway injury or continuous exposure to certain noxious environmental agents (eg, allergens or irritants). An airway that undergoes such an insult responds quickly with bronchospasm and cough, followed by inflammation, edema, and mucus production. This helps explain the fact that apparent chronic bronchitis in children is often actually asthma.Mucociliary clearance is an important primary innate defense mechanism that protects the lungs from the harmful effects of inhaled pollutants, allergens, and pathogens.[4] Mucociliary dysfunction is a common feature of chronic airway diseases.The mucociliary apparatus consists of 3 functional compartments: the cilia, a protective mucus layer, and an airway surface liquid (ASL) layer, which work together to remove inhaled particles from the lung. Animal study data have identified a critical role for ASL dehydration in the pathogenesis of mucociliary dysfunction and chronic airway disease.[5] ASL depletion resulted in reduced mucus clearance and histologic signs of chronic airway disease, including mucous obstruction, goblet cell hyperplasia, and chronic inflammatory cell infiltration. Study animals experienced reduced bacterial clearance and high pulmonary mortality as a result.The role of irritant exposure, particularly cigarette smoke and airborne particulates, in recurrent (wheezy) bronchitis and asthma is becoming clearer. Kreindler et al demonstrated that the ion transport phenotype of normal human bronchial epithelial cells exposed to cigarette smoke extract is similar to that of cystic fibrosis epithelia, in which sodium is absorbed out of proportion to chloride secretion in the setting of increased mucus production.[6] These findings suggest that the negative effects of cigarette smoke on mucociliary clearance may be mediated through alterations in ion transport.McConnell et al noted that organic carbon and nitrogen dioxide airborne particulates were associated with the chronic symptoms of bronchitis among children with asthma in southern California.[7] A chronic or recurrent insult to the airway epithelium, such as recurrent aspiration or repeated viral infection, may contribute to chronic bronchitis in childhood. Following damage to the airway lining, chronic infection with commonly isolated airway organisms may occur. The most common bacterial pathogen that causes lower respiratory tract infections in children of all age groups is Streptococcus pneumoniae. Nontypeable Haemophilus influenzae and Moraxella catarrhalis may be significant pathogens in preschoolers (age < 5 y), whereas Mycoplasma pneumoniae may be significant in school-aged children (ages 6-18 y).Children with tracheostomies are often colonized with an array of flora, including alpha-hemolytic streptococci and gamma-hemolytic streptococci. With acute exacerbations of tracheobronchitis in these patients, pathogenic flora may include Pseudomonas aeruginosa and Staphylococcus aureus (including methicillin-resistant strains), among other pathogens. Children predisposed to oropharyngeal aspiration, particularly those with compromised protective airway mechanisms, may become infected with oral anaerobic strains of streptococci.
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