Fiche de révision : Respiratory Physiology and Diagnostics

📋 Course Outline

1. Clinical Respiratory Assessment
2. Airway and Alveolar Structure
3. Pulmonary Circulation and Gas Transfer
4. Lung Volumes and Spirometry
5. Ventilatory Dysfunction and Mechanics
6. Gas Exchange and Disease Patterns
7. Respiratory Imaging Procedures
8. Respiratory Medical Techniques

📖 1. Clinical Respiratory Assessment

📝 Essential Points

★ Must-know

• The cardinal symptoms of respiratory-system disease are cough and dyspnea.

⚡ Dyspnea may have pulmonary or non-pulmonary causes and may be acute or chronic; chest tightness or inability to take a deep breath suggests obstructive lung disease, whereas air hunger or a sense of suffocation suggests congestive heart failure.

📌 Cough is classified as acute when it lasts less than 3 weeks, subacute when it lasts 3–4 weeks, and chronic when it lasts more than 8 weeks.

⚡ Wheezing suggests airway disease such as asthma or COPD, whereas stridor suggests upper-airway obstruction.

Further detail

• On physical examination, dull percussion suggests pleural effusion and hyper-resonant percussion suggests pneumothorax.

• Tactile fremitus increases with a mass or consolidation and decreases with pleural effusion.

💡 Memory Hook

Symptoms, signs, and context

📖 2. Airway and Alveolar Structure

🔑 Key Concepts & Definitions

• Respiratory zone : Consists of the respiratory bronchioles, alveolar ducts, and alveolar sacs, where gas exchange occurs.

📝 Essential Points

★ Must-know

⚡ The conducting zone extends from the nose to the terminal bronchioles, transports gas without gas exchange, and constitutes an anatomic dead space of about 150 mL of air.

• Type I pneumocytes cover 96–98% of the alveolar surface area and perform gas exchange.

Further detail

• Type II pneumocytes cover 2–4% of the alveolar surface area, are small cuboidal cells located at alveolar corners, produce surfactant, and may become Type I pneumocytes when needed.

💡 Memory Hook

Conducting carries; respiratory exchanges

📖 3. Pulmonary Circulation and Gas Transfer

📝 Essential Points

★ Must-know

⚡ The lungs have a dual blood supply consisting of pulmonary circulation and bronchial circulation.

• Pulmonary circulation carries deoxygenated blood to the respiratory bronchioles, alveolar ducts, and alveoli, and pulmonary veins return blood to the left atrium.

• Bronchial circulation carries oxygenated blood to the conducting airways and surrounding tissues, can undergo angiogenesis, and receives 1–2% of cardiac output.

⚡ Successful oxygenation and carbon-dioxide elimination require ventilation, perfusion, and diffusion.

Further detail

• About one-third of bronchial blood returns to the right atrium through bronchial veins and two-thirds returns to the left atrium through pulmonary veins.

💡 Memory Hook

Ventilation, perfusion, diffusion

📖 4. Lung Volumes and Spirometry

🔑 Key Concepts & Definitions

• Spirometry : A physiological test that measures how a person inhales and exhales air volumes as a function of time, using volume or flow as its primary signal.
• Forced vital capacity : The volume delivered during an expiration performed as forcefully and completely as possible after full inspiration.
• Forced expiratory volume : In one second is the volume delivered during the first second of a forced vital capacity maneuver.

📝 Essential Points

★ Must-know

• The four basic lung volumes are inspiratory reserve volume, tidal volume, expiratory reserve volume, and residual volume.

• The four lung capacities are inspiratory capacity, functional residual capacity, vital capacity, and total lung capacity, with each capacity formed by the sum of two or more lung volumes.

Further detail

• Residual volume, total lung capacity, and functional residual capacity cannot be directly measured by spirometry.

💡 Memory Hook

Volumes build capacities

📖 5. Ventilatory Dysfunction and Mechanics

📝 Essential Points

★ Must-know

⚡ An obstructive ventilatory defect is caused by hindrance to airflow and is characterized by decreased airflow and a decreased FEV1/FVC ratio.

⚡ A restrictive ventilatory defect results from inability to expand the alveoli and is characterized by decreased lung volume, including decreased total lung capacity and forced vital capacity.

• FEV1/FVC is considered low when it is less than 70%, and FVC is considered low when it is less than 80% of predicted.

Further detail

• Restrictive causes can be remembered as P-A-I-N-T:

  • pleura
  • alveoli
  • interstitium
  • neuromuscular disease
  • and thoracic abnormalities

• Work of breathing increases with substantially increased ventilation required by exercise or metabolic acidosis, with increased mechanical load from reduced compliance or increased airflow resistance, or with both.

💡 Memory Hook

Obstruction narrows; restriction limits expansion

📖 6. Gas Exchange and Disease Patterns

🔑 Key Concepts & Definitions

• Ventilation-perfusion heterogeneity : A mismatch between alveolar ventilation and perfusion, including ventilation of unperfused lung distal to pulmonary embolism as wasted ventilation and perfusion of non-ventilated lung as a shunt.

📝 Essential Points

★ Must-know

⚡ In perfusion-limited gas exchange, gas equilibrates with pulmonary capillary blood near the beginning of the capillary, so further transfer increases mainly by increasing blood flow.

⚡ In diffusion-limited gas exchange, gas does not equilibrate by the end of the pulmonary capillary; carbon monoxide and oxygen may behave this way during strenuous exercise and in emphysema or fibrosis.

• Idiopathic pulmonary fibrosis causes increased elastic recoil, low TLC, FRC, RV, and FVC, normal airway resistance, reduced diffusing capacity, and low oxygenation.

• Acute asthma causes airway narrowing from smooth-muscle constriction, inflammation, and bronchial thickening, with decreased FEV1/FVC, elevated FRC and RV, normal TLC, and normal diffusing capacity.

Further detail

• Severe emphysema causes decreased elastic recoil, decreased FEV1/FVC, elevated TLC, FRC, and RV, and decreased FVC and FEV1.

💡 Memory Hook

Mismatch wastes or shunts

📖 7. Respiratory Imaging Procedures

📝 Essential Points

★ Must-know

• Routine chest radiography includes posteroanterior, lateral, and lateral-decubitus views.

• Ultrasound is non-ionizing and may guide thoracentesis and biopsy of peripheral lung, pleural, and chest-wall lesions.

• Computed tomography assesses hilar and mediastinal disease, contrast distinguishes vascular from non-vascular structures, CT can guide pulmonary-mass biopsy, and high-resolution chest CT assesses interstitial lung disease.

⚡ PET scanning identifies malignant lung lesions through their increased glucose uptake, but false negatives occur with carcinoid tumors, bronchoalveolar carcinoma, and lesions smaller than 1 cm, while false positives occur with pneumonia and granulomatous disease.

Further detail

• Pulmonary angiography demonstrates pulmonary embolism by showing a filling defect or abrupt termination of a pulmonary vessel.

💡 Memory Hook

From radiography to PET

📖 8. Respiratory Medical Techniques

📝 Essential Points

★ Must-know

• Thoracentesis has diagnostic and therapeutic purposes and may be ultrasound guided.

• Bronchoscopy directly visualizes the tracheobronchial tree and has both diagnostic and therapeutic purposes.

• Medical thoracoscopy or pleuroscopy inspects the pleural surface, samples or drains pleural fluid, and permits pleural biopsy under conscious sedation and local anesthesia.

• Video-assisted thoracoscopic surgery is a standard technique for diagnosing and managing pleural and parenchymal lung disease, allowing pleural visualization, lung biopsy, nodule removal, lobectomy, and pneumonectomy under general anesthesia, while being less invasive than open thoracotomy.

Further detail

⚡ Sputum may be collected through spontaneous expectoration or sputum induction.

⚡ Thoracotomy provides a larger biopsy sample and can excise lesions that are too deep or too close to vital structures for removal by VATS.

💡 Memory Hook

Sample, scope, drain, or resect

📊 Synthesis Tables

Obstructive and Restrictive Defects

Thoracoscopic Procedures

⚠️ Common Pitfalls & Confusions

1. Chest tightness and air hunger are not interchangeable descriptions of dyspnea.
2. The conducting zone transports gas but is not the primary site of gas exchange.
3. Pulmonary circulation supplies the gas-exchange region rather than the conducting airways.
4. A capacity combines volumes, whereas a volume is a single measured compartment.
5. Obstruction primarily reduces airflow, whereas restriction primarily reduces lung volume.
6. Perfusion-limited exchange reaches equilibration early, unlike diffusion-limited exchange.
7. Ultrasound is described as safe for pregnant patients and children because it is non-ionizing.