Respiratory Disorders Overview

Acute Respiratory Distress Syndrome (ARDS)

• Severe ARDS is characterized by rapid-onset respiratory insufficiency, cyanosis, and severe arterial hypoxemia.
• ARDS develops within 72 hours of the initial insult in 85% of cases
• The overall hospital mortality rate is 38.5% for ARDS, with higher rates for more severe cases.

Respiratory Failure

• Respiratory failure within 1 week of a known clinical insult is one of the key features
• Chest imaging shows bilateral opacities, not fully explained by effusions, atelectasis, cardiac failure, or fluid overload.

Obstructive vs. Restrictive Pulmonary Diseases

• Obstructive Diseases: characterized by increased airway resistance due to airway obstruction.
  • Examples: Emphysema, Chronic Bronchitis, Bronchiectasis, Asthma
  • Key finding: Significantly decreased FEV1 (Forced Expiratory Volume in 1 second) with normal or slightly decreased FVC (Forced Vital Capacity).
• Restrictive Diseases: characterized by reduced lung expansion and decreased total lung capacity.
  • Examples: Chest wall disorders (severe obesity, pleura diseases, neuromuscular disorders), interstitial lung diseases (ARDS, pneumoconiosis, interstitial fibrosis)
  • Key finding: Reduced FVC, with normal or reduced FEV1.

Chronic Obstructive Pulmonary Disease (COPD)

• Chronic, irreversible airway obstruction, often associated with cigarette smoking
• Two main components: Emphysema and Chronic Bronchitis

Emphysema

• Definition: Permanent enlargement of air spaces distal to the terminal bronchioles, accompanied by destruction of their walls, without significant fibrosis.
• Types:
  • Centriacinar: Most common in cigarette smokers, affecting the upper lobes.
  • Panacinar: Affects lower lung zones, associated with α1-anti-trypsin deficiency.
  • Distal acinar (paraspetal): Proximal acinus is normal, distal portion involved, often striking adjacent to the pleura.
  • Irregular: Irregularly involved acinus, associated with scarring, often clinically asymptomatic, the most common form.

Chronic Bronchitis

• Definition: Persistent productive cough for at least 3 consecutive months in at least 2 consecutive years.
• Pathogenesis:
  • Cigarette smoking is the most important cause.
  • Other air pollutants (sulfur dioxide, nitrogen dioxide) induce hypertrophy of mucous glands in the trachea and goblet cells.
  • These irritants also cause inflammation with infiltration of macrophages, neutrophils, and lymphocytes.

Asthma

• Definition: Chronic inflammatory disorder of the airways causing recurrent episodes of wheezing, breathlessness, chest tightness, and cough.
• Hallmarks:
  • Intermittent, reversible airway obstruction
  • Chronic bronchial inflammation with eosinophils
  • Bronchial smooth muscle cell hypertrophy
  • Hyperreactivity
  • Increased mucus secretion

Asthma Subtypes:

• Atopic Asthma: Most common, type I IgE-mediated hypersensitivity reaction, usually begins in childhood, triggers include allergens in dust, pollen, animal dander, food, infections.
• Non-Atopic Asthma: No evidence of allergen sensitization, negative skin test, triggers include respiratory infections and inhaled air pollutants.
• Drug-Induced Asthma: Aspirin is the most striking example, patients experience recurrent rhinitis, nasal polyps, urticaria, and bronchospasm.
• Occupational Asthma: Triggered by fumes, organic dusts, chemical dusts, and gases, develops after repeated exposure to the relevant antigen.

Morphology of Asthma

• Most striking finding: Occlusion of bronchi and bronchioles by thick, tenacious mucous plugs with whorls of shed epithelium (Curschmann spirals).
• Numerous eosinophils and Charcot-Leyden crystals are also present.