Exhaustive Notes on Respiratory Medicine: Anatomy, Physiology, and Disease

Clinical Examination of the Respiratory System

General Observation:
- Hands: Check for digital clubbing, tar staining (nicotine), peripheral cyanosis, and signs of occupation. Look for a $CO_2$ retention flap and assess the radial pulse for rate and rhythm.
- Blood Pressure: Monitor for arterial paradox.
- Neck: Assess the Jugular Venous Pulse (JVP) for elevation or pulsatile nature.
- Face, Mouth, and Eyes: Look for pursed-lip breathing, central cyanosis, anaemia (conjunctival pallor), and Horner syndrome.
- Trachea: Ensure the trachea is central; measure the cricosternal distance (< 3 finger breadths suggests hyperinflation).
- Legs: Check for leg oedema (suggests salt/water retention, cor pulmonale, or venous thrombosis).
- General State: Note respiratory rate, cachexia (weight loss), fever, rash, sputum characteristics, and fetor (breath odour).
Thoracic Examination (Palpation, Percussion, and Auscultation):
- Inspection: Look for deformity (e.g., pectus excavatum, kyphoscoliosis), scars, intercostal indrawing, symmetry of expansion, hyperinflation, and paradoxical rib movement (indicates a low, flat diaphragm).
- Palpation: Assess for cardiac apex displacement, cervical lymphadenopathy, and expansion symmetry (from both front and back).
- Percussion: Differentiate between resonant, dull (consolidation), and "stony dull" (pleural effusion).
- Auscultation:
  - Breath sounds: Identify normal, bronchial, louder, or softer sounds.
  - Added sounds: Wheezes (obstruction), crackles (fluid/fibrosis), and rubs (pleurisy).
  - Vocal resonance: Absent in effusion; increased in consolidation.
  - Whispering pectoriloquy: Whispered voice heard clearly through a stethoscope over consolidation.
Sputum Types:
- Serous/Frothy/Pink: Indicates pulmonary oedema.
- Mucopurulent: Indicates bronchial or pneumonic infection.
- Purulent: Indicates established bronchial or pneumonic infection.
- Blood-stained: Potential cancer, tuberculosis, bronchiectasis, or pulmonary embolism.

Functional Anatomy and Physiology

Anatomy:
- Diaphragm: Innervated by the phrenic nerves ( $C3$ , $C4$ , and $C5$ ).
- Pleura: Parietal and visceral layers facilitate sliding contact; negative pressure in the pleural space balances elastic recoil.
- Conducting Airways: Total cross-section is smallest at the glottis and trachea, making them vulnerable to obstruction. Air is filtered, heated, and saturated with water vapour in the nose.
- Gas-Exchange Unit: The acinus comprises branching respiratory bronchioles and clusters of alveoli. The gas-to-blood distance is < 0.4\,m.
- Alveolar Cells: Type I pneumocytes (flattened epithelial) and Type II pneumocytes (cuboidal; produce surfactant to reduce surface tension and prevent collapse).
Control of Breathing:
- Originates in the respiratory motor neurons of the posterior medulla oblongata.
- Central Chemoreceptors: Located in the ventrolateral medulla; sense cerebrospinal fluid (CSF) $pH$ and are stimulated by arterial $PCO_2$ rise.
- Carotid Bodies: Sense hypoxaemia; primarily activated when arterial PO_2 < 8\,kPa ( $60\,mmHg$ ).
Ventilation and Perfusion ( $V/Q$ ):
- Hypoxia constricts pulmonary arterioles to match perfusion to ventilation; airway $CO_2$ dilates bronchi.
- Pulmonary Circulation: Operates at low pressure (approx. $24/9\,mmHg$ ). Hypertension occurs if vessels are destroyed (emphysema) or obstructed (thrombus).

Investigation of Respiratory Disease

Imaging:
- Chest X-ray (CXR): Standard is Posteroanterior (PA). Count ribs to check for hyperinflation (> 10 ribs visible posteriorly). Look for consolidation (shadowing with air bronchogram) or collapse (mediastinal shift toward the side of volume loss).
- Computed Tomography (CT): High-resolution thin-section scans assess parenchymal disease, bronchiectasis, and emphysema. CT Pulmonary Angiography (CTPA) is the gold standard for pulmonary thromboembolism.
- Positron Emission Tomography (PET): Uses radiotracer $^{18}F\text{-fluorodeoxyglucose (FDG)}$ to quantify glucose metabolism. Assessment uses the Standardised Uptake Value (SUV).
- Ultrasound: Distinguishes fluid from thickening; guides pleural asipiration or biopsy.
Respiratory Function Testing:
- Spirometry: Measures Forced Expired Volume in 1 second ( $FEV_1$ ) and Forced Vital Capacity ( $FVC$ ). Obstructive defect is defined as an $FEV_1/FVC$ ratio < 70\%.
- Reversibility: Defined as an increase of > 12\% and > 200\,mL in $FEV_1$ or $FVC$ after bronchodilators.
- Lung Volumes: Helium dilution (measures gas mixing with tidal breaths) or body plethysmography (measures total intrathoracic gas).
- Diffusion Capacity: Measured as Carbon Monoxide Transfer Factor ( $TLCO$ ) or $KCO$ (transfer factor per unit lung volume).

Presenting Problems

Cough:
- Acute: Viral infection, aspiration, or post-nasal drip.
- Chronic: COPD, asthma, GORD, ACE inhibitor usage, or lung cancer.
- Bovine Cough: Prolonged, low-pitched, inefficient cough caused by vocal cord palsy (recurrent laryngeal nerve involvement).
Breathlessness (Dyspnoea):
- Pathophysiology: Stimulated by sensory nerves (pneumothorax), mechanical load (fibrosis/obstruction), or metabolic triggers ( $CO_2$ , acidosis, hypoxia).
- Nijmegen Questionnaire: Used to assess breathing pattern disorders (psychogenic hyperventilation; score > 26 is significant).
Finger Clubbing: Symmetrical painless swelling. Common causes include lung cancer, bronchiectasis, cystic fibrosis, and idiopathic pulmonary fibrosis (IPF).
Haemoptysis: Major causes include bronchial cancer, bronchiectasis, tuberculosis, and pulmonary infarction. Massive haemoptysis may require bronchial artery embolisation.
Pleural Effusion: Accumulation of fluid in the pleural space.
- Light's Criteria (Exudate vs. Transudate): Exudate if Protein ratio > 0.5, LDH ratio > 0.6, or pleural LDH > 2/3 of upper limit of normal serum LDH.
- Common Causes: Transudates (Heart/liver/renal failure); Exudates (Pneumonia, TB, malignancy, pulmonary infarction).
- Empyema: Collection of pus; diagnosed by pH < 7.2, glucose < 3.3\,mmol/L, and high LDH.

Obstructive Pulmonary Diseases

Asthma:
- Chronic inflammatory disorder with airway hyper-responsiveness (AHR).
- Immediate Assessment of Severe Asthma: PEF $33--50\%$ predicted, Heart Rate $\ge 110\text{ bpm}$ , Respiratory Rate $\ge 25\text{ breaths/min}$ .
- Management: Stepwise approach from Step 1 (Low-dose inhaled glucocorticoid (ICS)) to Step 5 (Biologics like Omalizumab or Mepolizumab).
Chronic Obstructive Pulmonary Disease (COPD):
- Spectrum of Chronic Bronchitis (cough/sputum for $3$ months in $2$ years) and Emphysema (alveolar destruction).
- BODE Index: Predicts mortality based on BMI ( $B$ ), Obstruction ( $O$ ), Dyspnoea ( $D$ ), and Exercise capacity ( $E$ ).
- Oxygen Therapy (LTOT): Indicated if PaO_2 < 7.3\,kPa or $7.3--8\,kPa$ with cor pulmonale symptoms, polycythaemia, or hypertension.
Cystic Fibrosis (CF):
- Autosomal recessive; Chromosome 7; mutation in $CFTR$ gene (most common: $\Delta F508$ ). Causes thick secretions, bronchiectasis, malabsorption, and male infertility.

Infections of the Respiratory System

Pneumonia:
- CURB-65 Score: Confusion, Urea > 7\,mmol/L, Respiratory Rate $\ge 30/min$ , Blood Pressure (sBP < 90 or $dBP \le 60$ ), Age $\ge 65$ . Score $3+$ indicates severe pneumonia.
- Hospital-Acquired Pneumonia (HAP): Presents $\ge 48\,hours$ after admission.
Tuberculosis (TB):
- Caused by Mycobacterium tuberculosis. Primary infection forms a "Ghon focus" which spreads to hilar nodes (Ranke complex).
- Treatment: 6-month regimen (2 months of HRZE: Isoniazid, Rifampicin, Pyrazinamide, Ethambutol; followed by 4 months of HR).

Pulmonary Vascular Disease

Pulmonary Embolism (PE):
- Wells Score: Used to estimate clinical probability. Likelihood > 4\text{ points} warrants immediate CTPA.
- Management: Anticoagulation (LMWH, DOACs). Thrombolysis is reserved for massive/haemodynamically unstable PE.
Pulmonary Hypertension (PH):
- Defined as mean pulmonary artery pressure > 25\,mmHg at rest. Classifications: Type I (Arterial), Type II (Left Heart), Type III (Lung Disease), Type IV (CTEPH).