Pulmonary Pathophysiology – Pneumonia, COPD, Asthma & Bronchiectasis

Pulmonary Infections – Pneumonia

• Definition: infection of lung parenchyma ("lower respiratory tract infection")
• Classifications
  • Community-Acquired (CAP)
    • Acute: sudden (e.g., Streptococcus pneumoniae)
    • Chronic: gradual (e.g., TB)
  • Health-Care–Associated (HCAP): hospitalized \ge 2 days in last 90 days or long-term care in last 30 days
  • Hospital-Acquired (HAP): develops >48 h after admission
  • Ventilator-Associated (VAP): >48–72 h after intubation (prevent: head elevation, sub-glottic suction)
• Six pathogenetic routes
  1. Inhalation of aerosols (TB, Histoplasma, Legionella)
  2. Aspiration from oropharynx (risk: impaired gag)
  3. Direct inoculation (e.g., suction catheter)
  4. Contiguous spread (liver abscess → lung)
  5. Hematogenous spread (right-sided endocarditis, parasites)
  6. Reactivation of latent infection (TB, Pneumocystis)
• Typical CAP presentation: fever, cough ± sputum, pleuritic pain, dyspnea (elderly: dyspnea/confusion only)
• Bacterial vs Viral CAP
  • Bacterial: sudden, productive purulent/±hemoptysis, crackles/rhonchi, high fever
  • Viral: slower, dry/serous cough, wheezes, diffuse interstitial infiltrates
• Key diagnostics
  • Sputum: >25 leukocytes & <10 epithelial cells/HPF; AFB ⇒ TB
  • CXR: new infiltrate diagnostic but may be normal early/dehydrated/P. jiroveci

Tuberculosis (TB)

• Transmission: inhaled droplets of \textit{M. tuberculosis}
• Disease states
  • Latent TB: positive PPD, asymptomatic; risk of reactivation when immunity falls
  • Primary TB: active disease on first exposure (children, HIV)
• Clinical: fatigue, fever, night sweats, weight loss, chronic ±hemoptysis cough
• Radiology: upper-lobe infiltrate ±cavity (immune-competent); primary disease ⇒ hilar adenopathy
• Treatment: first-line combo— Isoniazid, Rifampin, Pyrazinamide, Ethambutol for 6–9 mo (often started before culture result)

Obstructive vs Restrictive Lung Disease

• Obstructive: ↓ airflow rate (e.g., CF, chronic bronchitis, asthma, bronchiectasis, emphysema, bronchiolitis)
• Restrictive: ↓ lung volumes (esp. IC & VC)

Chronic Obstructive Pulmonary Disease (COPD)

• Definition (ATS): chronic, progressive, not fully reversible airflow obstruction (emphysema + chronic bronchitis)
• Chronic bronchitis criterion: productive cough \ge 3 months/yr for \ge 2 consecutive years
• Emphysema: permanent enlargement distal to terminal bronchiole with alveolar wall destruction (no fibrosis)
  • Centrilobular: resp bronchioles, upper lobes, smoking
  • Panlobular: entire acinus, AAT deficiency
  • Bullous: large >1 cm airspaces
• Risk factors: smoking (primary), \alpha_1-antitrypsin deficiency, passive smoke, pollutants, dust/fumes, AW hyper-responsiveness, low SES, aging
• Pathophysiology: small airway inflammation (diam <2 mm), elastin loss → ↓ recoil, occasional reversible bronchospasm
• Classic signs/symptoms: chronic productive cough, exertional SOB, wheeze, late barrel chest, accessory muscle use, edema/cor pulmonale, altered mentation, asterixis
• Radiology: flattened diaphragm, hyperlucent fields, ↑ retrosternal space, ↓ peripheral vascularity
• Spirometry: post-bronchodilator \text{FEV}1/\text{FVC}
• Management
  • Smoking cessation (slows \text{FEV}1 decline) • PRN short-acting bronchodilator for all; add long-acting agents & rehab as GOLD stage advances • Inhaled steroids if frequent exacerbations (watch for pneumonia) • Acute exacerbation: bronchodilator, short systemic steroids, Abx if purulent, O2 (keep \text{SaO}_2>90\%), NIV if pH <7.3
  • LTOT \ge15 h/day improves survival; immunizations; consider surgery/transplant

Asthma

• Definition: chronic airway inflammation with variable/reversible obstruction & hyperreactivity
• Pathogenesis: genetic predisposition + triggers (allergen, infection, exercise, cold, smoke, stress) ⇒ IgE-mediated mast-cell degranulation ⇒ mediators ⇒ smooth-muscle contraction & mucus ⇒ ↓\text{FEV}_1
• Clinical: episodic wheeze, cough, dyspnea, chest tightness; absence of wheeze ≠ no asthma
• Diagnosis: post-BD \text{FEV}_1 \uparrow 12\% & \ge200 mL; if normal, positive methacholine challenge
• Treatment hierarchy
  • Controller: inhaled corticosteroids (mainstay); leukotriene inhibitors; long-acting \beta2-agonists (with ICS); tiotropium; anti-IgE (omalizumab) • Reliever: rapid \beta2-agonists
  • Cromolyn/nedocromil preventive in children/exercise
  • Severe attack: continuous \beta2 neb, IV steroids, O2, MV with permissive hypercapnia if needed

Bronchiectasis

• Irreversible bronchial dilation from chronic inflammation
• Morphologic types: cylindrical, varicose, cystic (saccular)
• Hallmark: large volumes of purulent, foul sputum (three-layer separation); hemoptysis common
• Diagnosis: high-resolution CT
• Management
  • Targeted antibiotics
  • Airway clearance: postural drainage, PEP, oscillatory devices, hypertonic saline/mannitol
  • Lung-expansion exercises, bronchodilators; O_2 & MV as required

Respiratory Therapist (RT) Roles

• Diagnostics: perform PFTs, collect sputum, assist bronchoscopy
• Management: deliver meds, airway hygiene, oxygen, NIV/MV, blood-gas monitoring
• Follow-up: smoking cessation, pulmonary rehab, LTOT, ventilatory support, infection control