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🫁 Respiratory System - NEET PG High-Yield Summary

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1. PULMONARY FUNCTION TESTS (PFTs) - Most Tested

Obstructive Pattern (Asthma, COPD, Bronchiectasis)

• FEV1/FVC < 0.7 (< 70%) - hallmark of obstruction
• FEV1 is decreased more than FVC
• TLC increased (air trapping)
• RV increased
• DLCO: decreased in COPD (emphysema), normal in asthma
• Flow-volume loop: concave (scooped-out) expiratory limb

Restrictive Pattern (ILD, Fibrosis, Kyphoscoliosis)

• FEV1/FVC ratio is normal or increased
• Both FEV1 and FVC reduced equally
• TLC decreased
• Flow-volume loop: narrow tall curve

GOLD Staging (COPD severity by post-bronchodilator FEV1):

Source: Symptom to Diagnosis, p. 614 (Murray & Nadel's Textbook of Respiratory Medicine)

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2. ASTHMA

Key Features (NEET PG Favorites)

• Reversible airflow obstruction (>12% and >200 mL increase in FEV1 after bronchodilator)
• Pathology: smooth muscle hypertrophy, submucosal edema, mucus plugging, eosinophilic infiltration
• Airway remodeling in chronic asthma (irreversible component)
• PEFR: best marker for monitoring
• Diurnal variation of PEFR > 20% is diagnostic
• Status asthmaticus: silent chest = most dangerous sign

Asthma vs COPD (High-yield distinction)

Asthma-COPD Overlap (ACO)

• Has features of both - mentioned in Harrison's 22E (2025)

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3. COPD

Types:

• Chronic Bronchitis (Blue Bloater): Productive cough > 3 months/year for > 2 years, hypercapnia, cor pulmonale common
• Emphysema (Pink Puffer): Loss of alveolar walls, barrel chest, pursed lip breathing, low DLCO

Cor Pulmonale

• Right heart failure secondary to lung disease
• Raised JVP, pedal edema, parasternal heave
• ECG: P pulmonale, right axis deviation

Treatment Ladder (GOLD):

• SABA (salbutamol) → LAMA (tiotropium) → LABA + ICS → Roflumilast (PDE4 inhibitor)
• O₂ therapy: if PaO₂ < 55 mmHg at rest (or < 60 with cor pulmonale)
• Only interventions that improve mortality in COPD: smoking cessation, long-term O₂ therapy, lung volume reduction surgery (selected)

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4. TUBERCULOSIS (TB)

Diagnosis

• Ziehl-Neelsen stain: AFB appear red on blue background
• Sputum smear microscopy: 3 samples (spot-morning-spot)
• Culture on Lowenstein-Jensen medium: gold standard (6-8 weeks)
• CBNAAT/GeneXpert: detects TB + rifampicin resistance in 2 hours
• Mantoux test (TST): Induration ≥ 10 mm = positive (≥ 5 mm in immunocompromised/HIV)
• IGRA (Interferon Gamma Release Assay): not affected by BCG

Radiological patterns

• Primary TB: Ghon focus (lower lobe) + hilar lymphadenopathy = Ghon complex (Primary complex)
• Post-primary/reactivation TB: Upper lobe cavitation (apical segment)
• Miliary TB: 1-3 mm nodules, uniformly distributed ("millet seeds")

RNTCP/DOTS Regimen (India)

• New case: 2HRZE + 4HR (Isoniazid, Rifampicin, Pyrazinamide, Ethambutol)
• Retreatment: 2HRZES + 1HRZE + 5HRE
• MDR-TB: Resistant to INH + Rifampicin

Side Effects of Anti-TB drugs (High-yield)

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5. PNEUMONIA

Community-Acquired Pneumonia (CAP) - Organisms by Pattern

Atypical Pneumonia Clues

• Mycoplasma: Cold agglutinins positive, bullous myringitis, responds to macrolides
• Legionella: Water/AC systems, hyponatremia, relative bradycardia, Pontiac fever
• Pneumocystis jirovecii (PCP): HIV patient, CD4 < 200, bilateral ground-glass opacities, LDH raised

Source: Grainger & Allison's Diagnostic Radiology; Robbins Pathology

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6. PLEURAL EFFUSION

Light's Criteria (Exudate - any one criterion met):

1. Pleural fluid protein / Serum protein > 0.5
2. Pleural fluid LDH / Serum LDH > 0.6
3. Pleural fluid LDH > 2/3 upper limit of normal serum LDH

• If transudates are misclassified as exudates by Light's criteria → check serum albumin - pleural fluid albumin > 1.2 g/dL (confirms transudate)

Common Causes

Key Features:

• Hepatic hydrothorax: 85% right-sided; TIPS may help; NEVER chest tube drain
• Hemorrhagic effusion: Malignancy, TB, trauma, PE

Source: Murray & Nadel's Textbook of Respiratory Medicine; Fishman's Pulmonary Diseases

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7. LUNG CANCER

Types & High-Yield Points

Paraneoplastic Syndromes

• SCLC: SIADH, Cushing (ectopic ACTH), Lambert-Eaton syndrome, ACTH
• Squamous cell: Hypercalcemia (PTHrP)
• Adenocarcinoma: Hypertrophic pulmonary osteoarthropathy (HPOA)

Pancoast Tumor (Superior sulcus tumor)

• Apex of lung → invades brachial plexus, sympathetic chain
• Features: Horner's syndrome (ptosis, miosis, anhidrosis), arm pain/weakness (C8-T1)

SVC Syndrome

• Most common cause: SCLC → compresses SVC
• Features: facial/arm edema, JVP raised, headache on bending

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8. INTERSTITIAL LUNG DISEASE (ILD)

Common ILDs

Sarcoidosis Stages (Chest X-ray)

• Stage 0: Normal
• Stage 1: Bilateral hilar lymphadenopathy (BHL) only
• Stage 2: BHL + pulmonary infiltrates
• Stage 3: Pulmonary infiltrates only (no BHL)
• Stage 4: Pulmonary fibrosis

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9. RESPIRATORY FAILURE

ABG in COPD Exacerbation

• Hypoxia + Hypercapnia + Respiratory acidosis
• O₂ should be given carefully (target SpO₂ 88-92%) to avoid suppressing hypoxic drive

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10. PULMONARY EMBOLISM (PE)

Clinical Features

• Sudden dyspnea, pleuritic chest pain, hemoptysis, tachycardia
• Massive PE: hypotension, syncope, raised JVP

Investigations

• D-dimer: High sensitivity, low specificity (rule-out test)
• CTPA: Investigation of choice (gold standard)
• V/Q scan: If CTPA contraindicated
• ECG: S1Q3T3 pattern (right heart strain), sinus tachycardia (most common ECG finding)

Wells Score (Pre-test probability)

• Used before D-dimer or imaging

Treatment

• Heparin (LMWH) → Warfarin / DOACs (rivaroxaban, apixaban)
• Massive PE: Thrombolysis (tPA) or surgical embolectomy

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11. QUICK-FIRE NEET PG FACTS

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