Chest Wall, Pleural, and Pulmonary Vascular Disorders: Advanced Pathophysiology Notes

Pneumothorax

• Definition: Air or gas in the pleural space, putting pressure on the lung, potentially leading to lung collapse.
• Types:
  • Spontaneous: Occurs without injury, often due to bleb rupture.
    • Primary: In healthy individuals (20-40 years old).
    • Secondary: Due to underlying disorders (e.g., COPD, cystic fibrosis).
  • Traumatic: From injury (e.g., rib fracture, gunshot wound, surgical complication).
• Open Pneumothorax:
  • Mechanism: Air enters and exits the pleural space through an external wound.
  • Intrapleural pressure: Equal to atmospheric pressure.
  • Lung collapse: On affected side; pressure does not build.
  • Symptoms: Sudden chest pain, shortness of breath, rapid/shallow breathing, fast heart rate, hypoxia, potential absent/decreased breath sounds, hyperresonance to percussion.
• Tension Pneumothorax:
  • Mechanism: One-way valve effect; air enters during inspiration but cannot escape, causing progressive pressure buildup.
  • Intrapleural pressure: Builds significantly.
  • Lung collapse: On affected side with severe mediastinal shift to the opposite side.
  • Life-threatening emergency: Compromises venous return, leading to severe hypotension, shock, tracheal deviation, and severe hypoxemia.

Pleural Effusion

• Definition: Accumulation of fluid in the pleural space.
• Pathophysiology: Disruption in hydrostatic pressure, oncotic pressure, capillary permeability, or lymphatic drainage.
• Five Types:
  • Transudate:
    • Fluid: Clear, watery, low-protein.
    • Pathophysiology: Increased hydrostatic pressure (e.g., heart failure) or decreased oncotic pressure (e.g., cirrhosis, nephrotic syndrome).
  • Exudate:
    • Fluid: Cloudy, thicker, protein-rich, containing immune cells.
    • Pathophysiology: Increased capillary permeability or pleural inflammation (e.g., infection, malignancy, pulmonary embolism).
  • Empyema (Pyothorax):
    • Fluid: Purulent (pus), thick fluid with dead WBC, bacteria, tissue debris.
    • Pathophysiology: Infection leads to massive neutrophilic infiltration.
  • Hemothorax:
    • Fluid: Sanguineous (blood).
    • Pathophysiology: Bleeding into the pleural space, increasing pressure and compressing the lung (e.g., trauma, surgery, cancer).
  • Chylothorax:
    • Fluid: Milky, containing fat and lymph.
    • Pathophysiology: Disruption or obstruction of the thoracic duct.

Pulmonary Vascular Disease

Virchow's Triad

• Three conditions predisposing to thrombus formation:
  1. Endothelial injury: Damage to the vessel lining (e.g., atherosclerosis, hypertension, trauma).
  2. Stasis of blood flow: Slowed flow (e.g., immobility, heart failure, varicose veins).
  3. Hypercoagulability: Increased tendency to clot (e.g., inherited mutations, cancer, pregnancy).

Pulmonary Embolism (PE)

• Definition: Blood clot (thrombus) forms, usually in deep veins of lower extremities, then travels to and lodges in the pulmonary vasculature.
• Pathophysiology: Obstructs blood flow, impairs gas exchange, increases pulmonary pressure, causes V/Q imbalances, and potentially pulmonary infarction, hypertension, and decreased cardiac output.
• Symptoms: Sudden dyspnea, chest pain, tachypnea, tachycardia, potentially hemoptysis.
• Prevention: Early mobilization, compression stockings, anticoagulants.
• Treatment: Anticoagulation, thrombolytics, thrombectomy.

Pulmonary Hypertension (PH)

• Definition: Mean pulmonary artery pressure >25 mmHg at rest (normal: 15-18 mmHg).
• Five Groups (WHO Classification):
  • Group 1: Pulmonary Arterial Hypertension (PAH): Idiopathic, heritable, drug-induced, or associated with conditions (e.g., connective tissue disease).
  • Group 2: PH due to left-sided heart disease: Most common cause (e.g., heart failure, mitral valve disease); backward transmission of elevated left atrial pressures.
  • Group 3: PH due to lung diseases and/or hypoxia: (e.g., COPD, interstitial lung disease); chronic hypoxemia leads to pulmonary vasoconstriction.
  • Group 4: Chronic thromboembolic PH (CTEPH).
  • Group 5: PH with unclear/multifactorial mechanisms.
• PAH Pathophysiology (Group 1):
  • Endothelial dysfunction and imbalance: Increased vasoconstrictors (Thromboxane, Endothelin), decreased vasodilators (Prostacyclin, Nitric Oxide).
  • Inflammation and remodeling: Fibrosis, smooth muscle proliferation, permanent arteriolar narrowing, increased pulmonary vascular resistance (PVR).
  • Leads to right ventricular hypertrophy (RVH) and heart failure.

Cor Pulmonale

• Definition: Right ventricular hypertrophy and/or dilation due to pulmonary hypertension, caused by diseases of the lungs or pulmonary vasculature.
• Pathophysiology: Chronic high pressure in pulmonary arteries causes the right ventricle to work harder, leading to hypertrophy and eventually right heart failure.

Obstructive vs. Restrictive Lung Disease

Bronchiectasis vs. Bronchiolitis

Pneumonia

• Definition: Infection of the lower respiratory tract, caused by bacteria, viruses, or fungi.
• Pathophysiology: Inflammation and fluid accumulation in alveoli.
• Types: Community-acquired, hospital-acquired, aspiration, viral.

Acute Respiratory Distress Syndrome (ARDS)

• Definition: Lungs (alveolar-capillary membrane) become inflamed and filled with fluid, eventually leading to tissue remodeling.
• Triggers: Severe infections (pneumonia, sepsis), trauma (chest injuries), inhalation injury, near-drowning, massive blood transfusions.
• Pathophysiology: Increased permeability of alveolar-capillary membrane
  ightarrow pulmonary edema
  ightarrow fluid in alveoli blocks gas exchange and dilutes surfactant.
• Stages:
  1. Exudative (Day 1-7): Alveolar flooding, hypoxemia, lung inflammation/stiffness.
  2. Proliferative (Day 7-21): Lung repair attempts with fibroblast activity.
  3. Fibrotic (After Day 21): Lungs become thickened and stiff (fibrosis), leading to long-term disability.

Asthma

• Definition: Chronic inflammatory disease of airways, characterized by bronchoconstriction, hyperresponsiveness, inflammation, and increased mucus production.
• Pathophysiology: Airway inflammation
  ightarrow edematous and hyperreactive airways
  ightarrow exaggerated bronchoconstriction in response to stimuli.
• Key Cellular Players: Mast cells, eosinophils, Th2 lymphocytes, goblet cells, smooth muscle cells.
• Airflow Obstruction: Caused by smooth muscle constriction, mucus plugging, and swelling of airway walls; typically reversible.
• Phases:
  • Early phase (within minutes): Bronchoconstriction, cough, wheezing, shortness of breath, driven by mast cells.
  • Late phase (4-12 hours later): Inflammation, mucus production, more severe/prolonged symptoms, involving eosinophils and T-cells.
• Structural Changes (Airway Remodeling): In poorly controlled chronic asthma, these become irreversible:
  • Thickening of basement membrane.
  • Smooth muscle hypertrophy.
  • Increased goblet cells.
  • Fibrosis of the airway wall.

Chronic Obstructive Pulmonary Disease (COPD)

• Definition: Group of progressive lung diseases causing airflow limitation that is not fully reversible; worsens over time.
• Main Types: Chronic bronchitis and emphysema.
• General Pathophysiology: Chronic inflammation (from irritants like smoking)
  ightarrow narrowing of airways, increased mucus, destruction of alveolar walls
  ightarrow airflow obstruction, especially during exhalation.

Chronic Bronchitis

• Definition: Hyper-secretion of mucus and chronic productive cough for \%>!3 months/year for \%>!2 consecutive years.
• Key Feature: Airway inflammation, bronchial edema, smooth muscle hypertrophy/hyperplasia, mucus accumulation, air trapping.
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