Obstructive Lung Diseases Overview

Obstructive Lung Diseases

• Characterized by increased resistance to exhaling air
• Difficulty exhaling air from the lungs
• Causes of resistance include issues in airway lumen, wall, or supporting structures
  • Lumen: Excess mucus production
  • Wall: Inflammation, bronchoconstriction
  • Supporting structures: loss of elastic recoil (emphysema)
• Common diseases include asthma, COPD, Alpha-1 Antitrypsin Deficiency (AATD), Bronchiectasis, and Cystic Fibrosis (CF)

Asthma

• Defining features: variable expiratory airflow limitation, bronchial hyperresponsiveness, and airway inflammation
• Airflow obstruction mechanisms: bronchospasm, mucus hypersecretion, and edema
  • Bronchospasm: constriction of air passages
  • Mucus hypersecretion: blockage of airways
  • Edema: swelling thickening airway walls
• Pathophysiology: exposure to allergen or stimuli triggers inflammatory process mediated by inflammatory mediators
  • Mediator release causes bronchoconstriction, mucus hypersecretion, vasodilation, and edema, narrowing airways and causing breathing difficulty
  • Involved cells and mediators: mast cells, histamine, cytokines, leukotrienes
• Triggers: allergens, viral infections, exercise, cold air, air pollution, medications, emotions, irritants
• Pulmonary function tests: decreased FEV1, decreased FEV1/FVC ratio, and decreased peak expiratory flow rate during exacerbations
  • FEV1: reduced amount of air exhaled in one second
  • FEV1/FVC: ratio reduced as FEV1 decreases more than FVC, Peak flow: Reflects maximum speed of air expelled
  • Increased residual volume and total lung capacity
• Bronchodilator reversibility: Increase in FEV1 by >12% and 200mL after short-acting beta-2 agonist
• Treatment: long-term control medications and acute relievers
  • Long-term: Corticosteroids, long-acting beta-2 agonists, leukotriene modifiers, biologic agents
  • Acute: Short-acting beta-2 agonists

Chronic Obstructive Pulmonary Disease (COPD)

• Defining features: chronic respiratory symptoms and persistent, often progressive airflow obstruction
• Encompasses emphysema and chronic bronchitis, often with overlapping features
• Emphysema: loss of lung elasticity, abnormal enlargement of airspaces, and destruction of alveolar walls
  • Inadequate recoil tension leads to airway collapse, air trapping, and increased residual volume
  • Air trapping causes hyperinflation
• Chronic Bronchitis: chronic cough with sputum production for at least three months a year for two consecutive years
  • Large and small airways are affected with obstruction present in both
  • Inflammation and fibrosis of bronchial wall, hypertrophy of submucosal glands, mucus hypersecretion, loss of elastic lung fibers and alveolar tissue
  • Leads to excess mucus, inflammation, decreased elastic recoil, air trapping, and decreased gas exchange
• Pulmonary Function Tests: decreased FEV1 and decreased FEV1/FVC ratio
  • Reduced FEV1/FVC ratio (even after bronchodilator)
  • Increased lung volumes (residual volume, functional residual capacity, and total lung capacity)
• Smoking: most common risk factor (related to about 75% of cases)
• Treatment: inhaled bronchodilators, inhaled corticosteroids, supplemental oxygen

Other Obstructive Conditions

• Alpha-1 Antitrypsin Deficiency (AATD): rare genetic disorder with low levels of alpha-1 antitrypsin protein
  • Increases risk of COPD and bronchiectasis; may also increase risk of cirrhosis and liver cancer
• Bronchiectasis: uncommon condition with airway wall damage causing permanent dilation of bronchi and bronchioles
  • Weakening of airway walls, impaired mucus clearance, leading to mucus accumulation and repeated lung infections
• Cystic Fibrosis (CF): rare genetic disorder causing thick, viscous secretions
  • In the lungs, leads to excessive mucus, airway obstruction, impaired mucus clearance, and repeated lung infections; can affect multiple organ systems

Restrictive Lung Diseases

• Inability to get sufficient air into the lungs and maintain normal lung volumes
• Characterized by reduced lung volumes
• Airway resistance: normal
• Contrast with obstructive lung disease: difficulty getting air into lungs vs. difficulty exhaling air; reduced airflow in obstructive, lung volume reduction in restrictive diseases
• Mechanisms: increased elastic recoil, respiratory muscle weakness, and mechanical restrictions
  • Elastic recoil: seen in interstitial lung disease
  • Respiratory muscle weakness decreases ability to inflate/deflate lungs
  • Mechanical restrictions impede lung expansion
• Pulmonary Function Tests: decreased FVC; FEV1 decreased or normal; FEV1/FVC ratio normal or increased
  • Total Lung Capacity (TLC): key indicator for defining restrictive lung disease (cannot be measured by spirometry)
  • All lung volumes are decreased (TLC, FRC etc)

Interstitial Lung Disease (ILD)

• Umbrella term for over 180 disorders
• Includes idiopathic pulmonary fibrosis, sarcoidosis, and pneumoconiosis
  • Pneumoconiosis: caused by inhalation of inorganic dust (e.g., asbestos, silica, talc)
  • Hypersensitivity pneumonitis: caused by inhalation of organic dust (e.g., moldy hay, bird droppings)
  • Sarcoidosis: systemic autoimmune disorder characterized by granulomas and alveoli inflammation
  • Idiopathic Pulmonary Fibrosis (IPF): most common type; no known cause; poor prognosis
  • Drug-Induced ILD: caused by over 350 medications (e.g., cancer chemotherapy, antimicrobial medications, biological agents, cardiovascular agents)
• Shared ILD features: fibrotic and inflammatory changes, immune cell accumulation, diffuse lung fibrosis
  • Increased elastic recoil, decreased lung compliance, decreased lung volumes, impaired oxygen diffusion
• Common ILD symptoms: dyspnea, tachypnea, non-productive cough, digital clubbing, cyanosis
  • Shortness of breath without wheezing, rapid breathing, dry cough, clubbing of fingers and toes, bluish discoloration
• ILD therapy goals: Identify and remove causative agent, suppress inflammation, and provide supportive care
• Treatments: corticosteroids, immunosuppressants, antifibrotic agents, supplemental oxygen

Other Restrictive Lung Diseases

• Kyphoscoliosis: outward and lateral curvature of the spine, stiffens chest wall, decreases compliance
• Respiratory Muscle Weakness: significant problem in neuromuscular diseases (e.g., muscular dystrophy, ALS)
• Pleural Effusion: abnormal fluid collection in pleural cavity; compresses lung
• Obesity: excess fat accumulation reduces lung volumes and compliance, affecting FRC and ERV; increases sleep apnea risk

Pulmonary Embolism (PE)

• Definition: substance lodges in pulmonary artery branch, obstructing blood flow
• Most common cause: thrombi from deep veins (DVT)
• Respiratory effects: obstruction leads to ventilated but non-perfused areas, impaired gas exchange, hypoxemia, hyperventilation; potential pulmonary infarction and necrosis, right heart strain
• Signs and symptoms: can range from no symptoms to sudden death; common symptoms: shortness of breath, chest pain, rapid breathing, and rapid heart rate
• Risk factors: Virchow's triad: vascular injury, blood stasis, hypercoagulability
• Specific risk factors: older age, VTE history, surgery, acute illness, paralysis, immobility, obesity, trauma, malignancies, pregnancy, estrogen-containing contraception, inherited coagulation disorders
• Diagnosis: CTPA, V/Q scan, D-dimer, compression ultrasound
• Treatment goals: prevent clot progression, reduce recurrence risk, prevent long-term complications, prevent death
• Medications: anticoagulants (unfractionated heparin, LMWH, fondaparinux, warfarin, DOACs); thrombolytics in severe cases
• Other treatments: catheter-based or surgical embolectomy
• Prevention: early ambulation, graduated compression stockings, intermittent pneumatic compression devices, anticoagulant medications