Pulmonary Pathophysiology – Key Vocabulary

Pneumonia (Pulmonary Infections)

Classification

• Community-Acquired (CAP): acute (hours–days) vs. chronic (days-months, e.g., TB)
• Health-Care Associated (HCAP): hospitalization \ge 2 days in last 90 or LTC stay within 30 days
• Hospital-Acquired (HAP): develops >48 h after admission
• Ventilator-Associated (VAP): >48–72 h post-intubation

Six Pathogenetic Mechanisms

• Inhalation of aerosolized agents (TB, Histoplasma, Legionella)
• Aspiration from oropharynx (common; risk: impaired gag reflex)
• Direct inoculation (e.g., suction catheter)
• Contiguous spread from adjacent infection (liver abscess ➔ lung)
• Hematogenous spread (right-sided endocarditis, parasites)
• Reactivation of latent infection (TB, Pneumocystis) when immunodeficient

Key Clinical Features

• CAP: fever, cough, purulent sputum, pleuritic pain, dyspnea (atypical in elderly)
• Bacterial: sudden, productive, purulent ± hemoptysis, crackles/rhonchi, high fever
• Viral: slower onset, dry/mucoid cough, sore throat, wheezing, malaise

Diagnostics

• Sputum: satisfactory if >25 WBC & <10 epithelial cells/hpf; AFB → TB
• Blood cultures in severe CAP
• CXR: new infiltrate needed for Dx; normal film possible early or in P.\ jiroveci

Radiology & Lab Highlights

• Bacterial: localized infiltrate, consolidation, leukocytosis, ↓PaO_2
• Viral: diffuse/patchy interstitial infiltrates; WBC normal, ↓PaO_2

Respiratory Therapist (RT) Role

• Collect sputum, assist bronchoscopy, chest PT, teach PEP/autogenic drainage, strict infection control

Tuberculosis (TB)

Epidemiology & Transmission

• Inhalation of droplet nuclei containing M.\ tuberculosis
• Incidence declined post-1950s antibiotics; spike 1985–1992 (AIDS)

Infection Types

• Latent TB: asymptomatic, positive PPD; risk of reactivation when debilitated
• Primary TB: active disease on initial exposure (children, HIV); persistent fever \approx70\%

Clinical & Imaging Clues

• Symptoms: fatigue, fever, night sweats, weight loss, chronic/hemoptysis cough
• CXR: upper-lobe infiltrates ± cavities (reactivation); primary TB shows hilar adenopathy

Treatment (first-line)

• Isoniazid, Rifampin, Pyrazinamide, Ethambutol; 6–9 month regimen; often started before cultures complete

Chronic Obstructive Pulmonary Disease (COPD)

Definition & Major Entities

• Progressive, not fully reversible airflow obstruction
• Emphysema: permanent enlargement beyond terminal bronchioles with wall destruction
• Chronic Bronchitis: productive cough \ge 3 months/yr for \ge 2 consecutive years

Risk Factors & Etiology

• Cigarette smoke (primary), \alpha_1-antitrypsin deficiency (2–3\% of cases)
• Passive smoke, pollution, dust/fumes, recurrent infections, low SES, aging

Pathophysiology of Airflow Limitation

• Small airway inflammation/obstruction (<2 mm)
• Loss of elastic recoil (septal destruction)
• Active bronchospasm (partial reversibility in \approx\tfrac23 patients)

Clinical Signs

• Chronic productive cough, wheeze, exertional SOB ➔ progressive dyspnea (6th–7th decade; earlier if AAT-def.)
• Late: barrel chest, accessory muscle use, cor pulmonale edema, mental status change

Radiology

• Hyperinflated lungs, flattened diaphragms, ↑retrosternal air, ↓vascular markings

Disease Severity (GOLD)

• Stage I: FEV_1 \ge 80\%
• Stage II: 50\% \le FEV_1 < 80\%
• Stage III: 30\% \le FEV_1 < 50\%
• Stage IV: FEV_1 < 30\% or <50\% with chronic respiratory failure

Management Highlights

• PRN short-acting bronchodilator for all; add long-acting agents, rehab as needed
• Inhaled steroids if repeated exacerbations (beware ↑pneumonia risk)
• Exacerbation: frequent \beta2 agonists, antibiotics if purulent sputum, short systemic steroids, O2 to keep SaO_2>90\%, NIV if pH <7.3
• Prevent progression: smoking cessation, LTOT \ge15 h/day, vaccinations

Emphysema Subtypes

• Centrilobular: respiratory bronchioles, upper lobes, smoking related
• Panlobular: entire acinus, diffuse; linked to \alpha_1-antitrypsin deficiency & aging
• Bullous: large >1 cm air spaces (bullae) in bronchioles & alveoli

Asthma

Definition

• Primary inflammatory airway disease with hyper-reactivity and reversible obstruction

Pathogenesis

• Genetic predisposition + triggers (allergens, infection, exercise, cold, smoke, stress)
• IgE-mediated mast-cell degranulation ➔ mediator release ➔ smooth muscle contraction ➔ ↓FEV_1

Clinical & Diagnostic Keys

• Episodic wheeze, dyspnea, cough, chest tightness; absence of wheeze ≠ absence of asthma
• Reversibility: post-bronchodilator \Delta FEV_1 \ge12\% & \ge200 mL
• If baseline normal, provocation with methacholine
• ABG during attack: hypoxemia; normal PaCO_2 signals impending failure

Pharmacotherapy Essentials

• Inhaled corticosteroids: cornerstone for long-term control
• \beta_2 agonists: most rapid bronchodilation; continuous neb in severe attack
• Leukotriene inhibitors: mild–moderate control
• Cromolyn/Nedocromil: prophylactic (mostly pediatric)
• Anticholinergics or Tiotropium: adjunct when control inadequate
• Anti-IgE (Omalizumab): allergic asthma uncontrolled on steroids

Emergency Management

• Repeated/continuous aerosolized \beta_2 agonist + high-dose IV steroids
• O_2 for hypoxemia, antibiotics if infection, MV with permissive hypercapnia if needed

Bronchiectasis

Definition & Types

• Irreversible bronchial dilation from chronic inflammation
• Patterns: Cylindrical (uniform), Varicose (irregular), Cystic/Saccular (distal sacs)

Hallmark Clinical Features

• Chronic copious purulent sputum (3-layer appearance), halitosis
• Dyspnea varies; frequent hemoptysis; digital clubbing; severe V/Q mismatch

Diagnosis & Management

• Fine-cut CT: diagnostic gold standard
• Antibiotics guided by sputum culture
• Airway clearance: postural drainage, cough maneuvers, humidification, inhaled mannitol
• Lung expansion (IS, deep breathing), bronchodilators, supplemental O_2
• MV if reversible ventilatory failure

Respiratory Therapist Roles (Obstructive & Infectious Diseases)

• Perform PFTs, physical assessment, sputum & ABG collection
• Administer medications, bronchial hygiene, oxygen, ventilatory support (invasive/NIV)
• Lead smoking cessation, pulmonary rehab, home O_2, ongoing education & advocacy