Airway obstruction, mucosal edema

Asthma is a respiratory illness characterized by variable and reversible airflow obstruction. Over 100 years ago. Osier, in his influential Textbook of Medicine (Osier, 1892), concluded that airway wall edema, bronchoconstriaion and mucus plugging are responsible for the airflow obstruction in asthma. Since that time, edema of the airway mucosa has been assumed to be one of the central features of asthma, but comparatively few studies have addressed the issue directly. Therefore, there is litde information about the onset, duration, magnitude, location, mechanism, consequences and management of mucosal edema in asthma. 

In the first definitive monograph on asthma, published in 1864, Sir Henry Hyde Salter concluded that the airway obstruction in asthma results from bronchoconstriction, mucus plu ng of the airway lumen, and edema of the airway wall (Salter, 1864). Salter s interpretations were probably based on clinical observations rather than on pathological examinations, because post-mortem findings were not described at that time. In fact, the initial histopathological studies of the airways of asthmatics did not recognize the presence of mucosal edema For example, in the first description of a post-mortem examination of a patient who died in status asthmaticus, Leyden concluded that the airflow obstruction resulted from mucus in the airways and that the walls [of bronchi]. ..are not essentially changed (Leyden, 1886). 

There are several consequences of an increase in the permeability of the blood vessels of the airway mucosa. Plasma leakage could result in mucosal edema and the movement of fluid into the airway lumen, both of which could contribute to airflow obstruction. In addition, plasma-derived inflammatory mediators could form in the mucosa and airway lumen, and extravasated plasma proteins could increase the viscosity of sputum. 

Asthma is a disease characterized by reversible airways obstruction and increased responsiveness of the airways to specific and nonspecific bronchocon-strictor stimuli. Indeed, the latter feature may be used in diagnosis of asthma (vide infra). Obstruction to the flow of air in asthma is the product of three factors smooth muscle contraction, mucosal edema, and augmented mucus secretion. Pathological features, such as infiltration of the airway walls with inflammatory cells (e.g., eosinophils, neutrophils), and the efficacy of antiinflammatory steroids in treating the disease have pointed to an important role of inflammation in the disease process. 

With high-level exposure, laryngeal edema, tracheobronchitis, and abmpt airway obstruction may occur. Irritation of the lower respiratory tract and lung parenchyma causes tracheobronchial mucosal sloughing, chemical pneumonitis, and nonoardiogenic pulmonary edema. 

Obstructive lung disease has been rarely associated with BD as well as trachea-bronchial ulcerations and stenosis. Ulcerative lesions may be found in the trachea and proximal airways. Mucosal edema may result in irregular narrowing of the airway (21-23). 

Asthma is a common chronic inflammatory disorder that affects the airway passages of the lungs. Primarily, asthma is characterized by reversible, episodic narrowing of the airway s smooth muscle secondary to hypersecretion of mucus, hyper-reactivity, and mucosal edema. The narrowing may be of sudden or prolonged onset, which accounts for the varying degrees of airway obstruction seen in this disease. The hallmark of airway obstruction is a reduction in the forced expiratory volume in 1 second (FEV and the ratio of FEVj to the forced vital capacity (FVC). 

Pulmonary function test (PFT) abnormalities occur frequently following allogeneic BMT. A decreased carbon monoxide diffusion (DLco) develops in up to 83% and restrictive and obstructive ventilatory defects in up to 35% and 23%, respectively, of allogeneic BMT recipients (3). Significant mucosal injury occurs in about 75% of BMT recipients. Upper airway inflammation due to mucositis may lead to laryngeal edema, dysphagia, and aspiration pneumonia. Life-threatening upper airway complications are more common in children. 

---