RESPIRATORY SYSTEM

1. ANATOMY OF THE RESPIRATORY SYSTEM

1.1 General Features & Importance

✔ The respiratory system facilitates gas exchange (O₂ intake, CO₂ elimination) and acid-base balance.
✔ Divided into Upper & Lower Respiratory Tracts.
✔ Works in coordination with the cardiovascular system for oxygenation and tissue perfusion.

1.2 Divisions of the Respiratory System

1.2.1 Upper Respiratory Tract

✔ Nose & Nasal Cavity → Air filtration, humidification, olfaction.
✔ Paranasal Sinuses → Lightens the skull, resonance to voice, mucus production.
✔ Pharynx → Nasopharynx, Oropharynx, Laryngopharynx – common passage for air and food.
✔ Larynx (Voice Box) → Contains vocal cords; prevents aspiration (epiglottis).

1.2.2 Lower Respiratory Tract

✔ Trachea → C-shaped cartilage rings, prevents collapse during inspiration.
✔ Bronchi → Right main bronchus (wider, more vertical) → prone to aspiration.
✔ Bronchioles → Lack cartilage, regulate airflow resistance.
✔ Alveoli → Functional units of gas exchange, surfactant production (Type II pneumocytes).

1.3 Histological Layers of the Respiratory Tract

✔ Mucosa → Pseudostratified columnar epithelium with cilia and goblet cells.
✔ Submucosa → Contains seromucous glands.
✔ Cartilage & Smooth Muscle → Found in trachea and bronchi, absent in alveoli.
✔ Alveolar Wall → Type I pneumocytes (gas exchange), Type II pneumocytes (surfactant).

1.4 Pulmonary Circulation & Lymphatics

✔ Pulmonary Arteries → Carry deoxygenated blood to lungs.
✔ Pulmonary Veins → Carry oxygenated blood to the heart.
✔ Bronchial Circulation → Supplies lung tissue.
✔ Lymphatic Drainage → Important in lung cancer metastasis.

2. PHYSIOLOGY OF THE RESPIRATORY SYSTEM

2.1 Mechanism of Breathing (Ventilation)

✔ Inspiration → Active process, diaphragm contraction (main muscle), external intercostals.
✔ Expiration → Passive process, elastic recoil; active during forced expiration (internal intercostals, abdominal muscles).

2.2 Lung Volumes & Capacities (PG Concept)

✔ Tidal Volume (TV) → Normal breathing (500 mL).
✔ Inspiratory Reserve Volume (IRV) → Additional air after inspiration.
✔ Expiratory Reserve Volume (ERV) → Additional air expelled after normal expiration.
✔ Residual Volume (RV) → Air left in lungs after forced expiration.
✔ Vital Capacity (VC) → TV + IRV + ERV (max. air exchange).
✔ Total Lung Capacity (TLC) → VC + RV.

2.3 Gas Exchange & Transport

✔ Occurs at the alveolar-capillary interface (Diffusion of O₂ & CO₂).
✔ O₂ Transport:

98% bound to hemoglobin.
2% dissolved in plasma.
✔ CO₂ Transport:
70% as bicarbonate (HCO₃⁻).
20% bound to hemoglobin (carbamino-Hb).
10% dissolved in plasma.

2.4 Control of Respiration

✔ Medullary Respiratory Centers → Basic rhythm (Dorsal & Ventral Respiratory Groups).
✔ Pontine Centers → Apneustic & Pneumotaxic Centers modulate breathing rate.
✔ Chemoreceptors:

Central (Medulla) → Respond to ↑ CO₂, ↓ pH.
Peripheral (Carotid & Aortic Bodies) → Respond to ↓ O₂.

3. PATHOLOGY OF THE RESPIRATORY SYSTEM

3.1 Upper Respiratory Tract Disorders

✔ Rhinitis → Inflammation of nasal mucosa (allergic, infectious).
✔ Sinusitis → Sinus infection due to obstruction.
✔ Laryngitis → Vocal cord inflammation, hoarseness.

3.2 Obstructive Lung Diseases

✔ Chronic Obstructive Pulmonary Disease (COPD) → Emphysema + Chronic Bronchitis.
✔ Asthma → Reversible bronchoconstriction, eosinophilic inflammation.
✔ Bronchiectasis → Permanent airway dilation due to chronic infection.

3.3 Restrictive Lung Diseases

✔ Interstitial Lung Disease (ILD) → Fibrosis, reduced lung compliance.
✔ Sarcoidosis → Non-caseating granulomas, hilar lymphadenopathy.

3.4 Pulmonary Infections

✔ Pneumonia → Bacterial (Streptococcus pneumoniae), Viral, Fungal.
✔ Tuberculosis (TB) → Caseating granulomas, Ghon focus.

3.5 Pulmonary Vascular Diseases

✔ Pulmonary Embolism (PE) → DVT dislodgement → sudden dyspnea, tachycardia.
✔ Pulmonary Hypertension → Mean PA pressure > 25 mmHg.

3.6 Neoplastic Diseases

✔ Lung Cancer → Small cell (poor prognosis) vs. Non-small cell carcinoma.
✔ Mesothelioma → Asbestos exposure-related pleural cancer.

4. CLINICAL EXAMINATION OF THE RESPIRATORY SYSTEM

IMPORTANCE:
✔ Essential for diagnosing respiratory diseases such as pneumonia, pleural effusion, tuberculosis, COPD, asthma, interstitial lung disease, and pulmonary embolism.
✔ Helps differentiate between obstructive and restrictive lung diseases.
✔ Identifies early warning signs of serious conditions like lung cancer or respiratory failure.

4.1 GENERAL APPROACH TO CLINICAL EXAMINATION

✔ Ensure patient comfort and proper positioning → Preferably sitting upright.
✔ Obtain informed consent before examination.
✔ Use adequate lighting and a quiet environment for auscultation.
✔ Maintain a structured approach → Inspection → Palpation → Percussion → Auscultation.

4.2 HISTORY TAKING (ESSENTIAL IN RESPIRATORY DISEASES)

Chief Complaints to Elicit

✔ Dyspnea (Shortness of Breath)

Acute (PE, pneumothorax, pneumonia) vs. Chronic (COPD, ILD).
Exertional dyspnea → Heart failure, COPD.
Positional dyspnea → Orthopnea (heart failure), Trepopnea (pleural effusion).
✔ Cough
Acute (<3 weeks) → Viral infections, pneumonia.
Chronic (>8 weeks) → Tuberculosis, GERD, chronic bronchitis.
Productive cough → Bronchiectasis, COPD, pneumonia.
Dry cough → ILD, asthma, ACE inhibitors.
✔ Hemoptysis (Blood in Sputum)
Common in tuberculosis, bronchiectasis, lung cancer, pulmonary embolism.
✔ Wheezing (Whistling Sound in Breathing)
Seen in asthma, COPD, anaphylaxis, foreign body aspiration.
✔ Chest Pain
Pleuritic (sharp, worsens with breathing) → Pneumonia, PE, pneumothorax.
Non-pleuritic → Musculoskeletal, cardiac causes.
✔ Weight Loss & Fever
Red flags for tuberculosis, lung cancer, chronic infections.

4.3 GENERAL PHYSICAL EXAMINATION

✔ Vital Signs →

Respiratory Rate (Normal: 12-20/min) → Tachypnea in pneumonia, PE.
Pulse Rate & BP → Tachycardia in hypoxia, cor pulmonale.
Temperature → Fever in infections like pneumonia, TB.
✔ Oxygen Saturation (SpO₂ using Pulse Oximetry)
Normal >95%; Hypoxia <90% → Requires oxygen support.
✔ Use of Accessory Muscles
Increased work of breathing in COPD, severe asthma.
✔ Cyanosis (Bluish discoloration of lips/nails)
Central Cyanosis → Lung diseases, respiratory failure.
Peripheral Cyanosis → Vasoconstriction, poor circulation.
✔ Clubbing of Fingers (Schamroth’s Sign)
Clubbing causes: CLIP → Cancer (lung), Lung abscess, ILD, Pulmonary fibrosis.

4.4 INSPECTION (LOOKING FOR RESPIRATORY SIGNS)

✔ Chest Shape & Symmetry

Barrel Chest → Seen in COPD (Hyperinflation).
Pectus Excavatum (Depressed sternum) → Restrictive lung issues.
Pectus Carinatum (Protruding sternum) → Rare, may affect lung function.
✔ Tracheal Deviation (Midline or Shifted?)
Toward diseased side → Lung collapse, fibrosis.
Away from diseased side → Large pleural effusion, pneumothorax.
✔ Respiratory Movements & Patterns
Paradoxical breathing → Diaphragmatic paralysis.
Kussmaul Breathing → Deep, rapid breaths (metabolic acidosis).
Cheyne-Stokes Breathing → Alternating hyperventilation & apnea (CHF, stroke).

4.5 PALPATION (FEELING FOR ABNORMALITIES)

✔ Position of Trachea

Displacement suggests lung collapse, pneumothorax, or pleural effusion.
✔ Chest Expansion (Symmetrical or Asymmetrical?)
Reduced on one side → Pneumothorax, pleural effusion.
✔ Tactile Vocal Fremitus (TVF)
Increased TVF → Lung consolidation (pneumonia).
Decreased TVF → Pleural effusion, pneumothorax.
✔ Palpation for Tenderness & Crepitus
Rib tenderness → Fractures, pleuritis.
Subcutaneous emphysema (Crepitus on palpation) → Air leakage from lungs.

4.6 PERCUSSION (TAPPING TO DETECT LUNG CHANGES)

✔ Normal Percussion Sound → Resonant.
✔ Dull Percussion (Fluid or Solid in Lungs) →

Pneumonia, Pleural Effusion, Lung Tumor.
✔ Hyperresonance (Increased Air in Lungs) →
Pneumothorax, COPD, Asthma Attack.

4.7 AUSCULTATION (LISTENING TO LUNG SOUNDS WITH STETHOSCOPE)

✔ Normal Breath Sounds → Vesicular (Soft, low-pitched).
✔ Decreased Breath Sounds → Pneumothorax, Pleural Effusion.
✔ Added Sounds (Abnormal)

Crackles (Fine or Coarse) → Pulmonary edema, pneumonia, fibrosis.
Wheezing (Expiratory Musical Sound) → Asthma, COPD.
Stridor (Inspiratory Crowing Sound) → Airway obstruction, croup.
Pleural Rub (Creaking Sound) → Pleuritis, PE.

4.8 SPECIAL TESTS FOR LUNG DISEASES

✔ Egophony → "E" sounds like "A" in lung consolidation.
✔ Bronchophony → Increased voice resonance in pneumonia.
✔ Whispered Pectoriloquy → Whispered sounds clearer in consolidation.

4.9 DIAGNOSTIC CORRELATIONS (EXAM-FOCUSED)

✔ Pneumothorax Signs

Absent breath sounds.
Hyperresonant percussion.
Tracheal deviation away.

✔ Pleural Effusion Signs

Decreased breath sounds.
Dull percussion.
Reduced chest expansion.

✔ COPD Signs

Barrel chest, pursed-lip breathing.
Decreased breath sounds, hyperresonance.

✔ Pneumonia Signs

Increased TVF, Egophony positive.
Crackles, bronchial breath sounds.

✔ Pulmonary Embolism Signs

Sudden dyspnea, tachycardia.
Clear lungs on auscultation.

5. HIGH-YIELD PG EXAM PEARLS

✔ COPD Diagnosis → FEV1/FVC < 70% post-bronchodilator.
✔ Pneumothorax Sign → Absent breath sounds, hyperresonance.
✔ TB Diagnosis → Ziehl-Neelsen stain, GeneXpert.
✔ PE Investigation → CT Pulmonary Angiography (Gold Standard).

CLINICAL INSIGHT DIALOGUES By Dr Jayaram Krishna M

Wednesday, March 19, 2025