Atlas of pathophysiology, 2 Edition

Part II - Disorders

Respiratory Disorders 

Chronic Bronchitis

Bronchitis is acute or chronic inflammation of the bronchi caused by irritants or infection. The distinguishing characteristic of bronchitis is obstruction of airflow. In chronic bronchitis, a form of chronic obstructive pulmonary disease, hypersecretion of mucus and chronic productive cough are present during 3 months of the year for at least 2 consecutive years.

Age Alert

Children of parents who smoke are at higher risk for respiratory tract infection, which can lead to chronic bronchitis.

Causes

·   Cigarette smoking

·   Exposure to irritants

·   Genetic predisposition

·   Exposure to organic or inorganic dusts

·   Exposure to noxious gases

·   Respiratory tract infection

Pathophysiology

Chronic bronchitis develops when irritants are inhaled for a prolonged time. The irritants inflame the tracheobronchial tree, leading to increased mucus production and a narrowed or blocked airway. As the inflammation continues, changes in the cells lining the respiratory tract increase resistance in the small airways, and severe imbalance in the ventilation-perfusion ([V with dot above]/[Q with dot above]) ratio decreases arterial oxygenation.

Chronic bronchitis causes hypertrophy of airway smooth muscle and hyperplasia of the mucous glands, increased numbers of goblet cells, ciliary damage, squamous metaplasia of the columnar epithelium, and chronic leukocytic and lymphocytic infiltration of bronchial walls. Hypersecretion of the goblet cells blocks the free movement of the cilia, which normally sweep dust, irritants, and mucus away from the airways. Accumulating mucus and debris impair the defenses and increase the likelihood of respiratory tract infections.

Additional effects include narrowing and widespread inflammation within the airways. Bronchial walls become inflamed and thickened from edema and accumulation of inflammatory cells, and smooth-muscle bronchospasm further narrows the lumen. Initially, only large bronchi are involved, but eventually all airways are affected. Airways become obstructed and close, especially on expiration, trapping the gas in the distal portion of the lung. Consequent hypoventilation leads to a [V with dot above]/[Q with dot above] mismatch and resultant hypoxemia and hypercapnia.

Signs and symptoms

·   Copious gray, white, or yellow sputum

·   Dyspnea and tachypnea

·   Cyanosis

·   Use of accessory muscles

·   Pedal edema

·   Jugular vein distention

·   Weight gain due to edema or weight loss due to difficulty eating and increased metabolic rate

·   Wheezing, prolonged expiratory time, and rhonchi

·   Pulmonary hypertension

Diagnostic test results

·   Chest X-rays show hyperinflation and increased bronchovascular markings.

·   Pulmonary function studies indicate increased residual volume, decreased vital capacity and forced expiratory flow, and normal static compliance and diffusing capacity.

·   Arterial blood gas analysis reveals decreased partial pressure of arterial oxygen and normal or increased partial pressure of arterial carbon dioxide.

·   Sputum analysis reveals many microorganisms and neutrophils.

·   Electrocardiography shows atrial arrhythmias; peaked P waves in leads II, III, and aVF and, occasionally, right ventricular hypertrophy.

Treatment

·   Smoking cessation

·   Avoidance of air pollutants

·   Antibiotics

·   Bronchodilators

·   Adequate hydration

·   Chest physiotherapy

·   Ultrasonic or mechanical nebulizers

·   Corticosteroids

·   Diuretics

·   Oxygen therapy

P.87

MUCUS BUILDUP IN CHRONIC BRONCHITIS

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