Respiratory Pathophysiology

Respiratory Pathophysiology

1. Overview of the Respiratory System

The respiratory system consists of:

• Thorax: Protects the respiratory organs inside.

• Airways – Lungs: Responsible for conducting air and gas exchange.

• Vascular system: Supplies blood to respiratory organs.

2. Thorax Structure

The thorax includes:

• Bones: Spine, ribs, sternum.

• Muscles:

• Inpiratory muscles: Diaphragm, external intercostals.

• Forced inspiratory muscles: Scalenes, sternocleidomastoid, anterior serratus, masseter, tongue, alar nasi.

• Expiratory muscles: Normally none, forced expiration includes internal intercostals and anterior abdominal wall.

3. Airway Structure

Airways are divided into:

• Cartilaginous airways: Trachea, bronchi.

• Membranous airways: Bronchioles (contain Ressell’s muscle for diameter contraction/dilation).

4. Functions of the Bronchial System

The bronchial system consists of two parts:

• Air conduction function: Trachea – bronchi, lined with mucosa, nourished by bronchial arteries.

• Respiratory function: Terminal bronchioles, alveolar duct, alveolar sac, nourished by pulmonary circulation.

5. Lungs

• Contains 300-500 million alveoli, the number depends on height and exercise.

• Alveolar epithelium includes lining cells and surfactant-producing cells.

• Anatomical surface area of alveoli: 80 m2.

• Functional surface area: 70 m2.

6. Pleura

• Consists of two layers: visceral and parietal, separated by the pleural cavity containing a thin layer of fluid.

• Negative pressure inside the pleural cavity.

7. Vascular System

• Originating from the aorta, nourishing the lung parenchyma and bronchi.

• Originating from the pulmonary artery, blood flow 6000-7000 l/day.

8. Respiration

• The process of gas exchange between organisms and the external environment, supplying O2 and eliminating CO2.

• Consists of 4 stages:

• Ventilation: Gas exchange between alveoli and the external environment, manifested by inspiration and expiration.

• Diffusion: Passive gas exchange between alveoli and blood.

• Transport: Carrying O2 from the lungs to cells, CO2 from cells to the lungs.

• Transmembrane exchange: Cellular respiration.

9. Ventilation Stage

• Function: Renewing air in the alveoli.

• Diffusion rate depends on:

• Pressure difference across the alveolar-tissue membrane.

• Total alveolar surface area.

• Thickness of the alveolar-tissue membrane.

• Solubility of each gas.

10. Transport Stage

• Transport efficiency depends on blood function and circulatory system.

11. Cellular Gas Exchange

• Depends on the pressure difference of gases on both sides of the cell membrane (cellular respiration intensity).

12. Cellular Respiration

• The process of using O2 to generate energy.

13. Respiratory Center

• Located in the medulla oblongata and pons.

• Regulating respiration involves 3 groups of neurons forming 3 centers: inspiration, expiration, and regulation.

14. Dorsal Respiratory Group (DRG)

• Generates the inspiratory rhythm (basic respiratory rhythm).

• Receives signals from the vagus (X) and glossopharyngeal (IX) nerves.

15. DRG Regulatory Center

• Determines the end of inspiration (duration of inspiration).

• Excited: Short inspiration, fast, shallow breathing.

• Inhibited: Long inspiration, slow, deep breathing.

16. Ventral Respiratory Group (VRG)

• Controls inspiration and expiration.

• Inactive during normal breathing.

• Active during increased ventilation (mobilizing abdominal muscles, forced respiratory muscles).

17. Influence of CO2, H+ and O2 on Respiration

• CO2 and H+ directly stimulate the respiratory center, increasing inspiration time and expiration.

• CO2 has a stronger effect than H+.

• High pCO2, low pH: Inhibition -> respiratory paralysis.

• O2 indirectly affects through receptors in the carotid artery (carotid sinus) and aorta.

• Low pO2: Loss of stimulating effect, emergence of respiratory inhibitory effect.

• Constant pO2, lower pH: CO2 becomes more likely to stimulate respiration.

• Constant pCO2, lower pH: O2 becomes more likely to stimulate respiration.

18. External Respiratory Function Tests

• Ventilation capacity testing: Assessing lung parenchyma function through gas exchange volume and assessing airways through air flow rate.

• Diffusion capacity testing: Assessing gas exchange between alveoli and blood.

19. Ventilation Capacity Testing

• Using spirometer.

• Gas exchange volume: Assessing lung parenchyma.

• Air flow rate: Assessing airway patency.

20. Respiratory Function Test Indices

• Vital capacity (VC): The maximum amount of air that the body can exchange with the environment in one breath, reflecting the number of alveoli currently functioning. Decreased when airflow is restricted.

• Forced expiratory volume in 1 second (FEV1): The maximum amount of air exhaled in the first second, reflecting the patency of the airways. Decreased in airflow obstruction.

• Tiffeneau index (FEV1/VC): 75%-80%, reflecting the ability to exhale in the first second.

• Tidal volume (TV): Volume of one inhalation/exhalation.

• Inspiratory reserve volume (IRV): Additional inhalation volume after normal inhalation.

• Expiratory reserve volume (ERV): Volume exhaled after normal exhalation.

• Residual volume (RV): The volume remaining after exhaling fully, increased in older age and certain diseases.

• Vital capacity (VC): The maximum volume exhaled after maximum inhalation, reflecting the number of alveoli and age.

• Forced vital capacity (FVC): Forced vital capacity.

• Total lung capacity (TLC): VC + RV.

21. Air Flow Rate

• Reflects airway patency.

• Depends on:

• Thorax expansibility: Structure and function of respiratory muscles, shape of the thorax.

• Airway patency.

• Air flow indices: FEV1, FEV1/VC, MVV, FVC/VC, MEFX%FVC.

22. Respiratory Affecting Diseases

• Neuro-muscular diseases:

• Central origin: Damage, inhibition, paralysis, destruction of the respiratory center (brain stem lesions, encephalitis, poisoning).

• From the center to the respiratory muscles: Cervical spinal cord injury, intercostal neuritis.

• Respiratory muscles: Thorax injury, myasthenia gravis, diaphragmatic paralysis.

• Skeletal diseases:

• Skeletal deformities: Too small compared to height.

• Joint stiffness: Restricted chest expansion.

• Kyphosis, scoliosis.

• Mobile rib cage…

• Decreased VC, FEV1, but Tiffeneau is normal.

• Lung diseases:

• Decreased surfactant production.

• Diffuse infiltrative lung diseases: Pulmonary fibrosis, pneumoconiosis, pulmonary edema, tuberculous pneumonia.

• Large lung lesions: Lobar pneumonia, bronchopneumonia.

• Decreased ventilation.

• Pleural diseases:

• Pleural thickening: Traction, difficult expansion.

• Pleural effusion.

• Decreased VC, TLC.

• Mildly decreased RV, significantly decreased FRV.

23. Surfactant

• A thin layer of fluid lining the inner surface of the alveoli.

• Protects the alveoli, helping them expand under the pressure of inhaled air.

• Surfactant deficiency: Requires very high pressure to expand the alveoli, exceeding the ability of the respiratory muscles.

• Harmful effects: Limiting alveolar compliance (compliance), limiting alveolar dilation (dilation).

24. Airway Diseases

• Obstruction: Increased resistance (inhalation), mobilization of accessory respiratory muscles.

• Small airway obstruction: Forced expiratory maneuver.

• Small airway obstruction in the first 1/3: Air flow rate depends on expiratory muscle strength, lung contractility, and the degree of obstruction.

• Small airway obstruction in the last 2/3: Depends on the degree of obstruction.

• Tracheal-bronchial obstruction: Located outside the lungs, inhalation: the narrowed area contracts, exhalation: the narrowed area expands. Expiratory flow rate/inspiratory flow rate >1.

25. Chronic Obstructive Pulmonary Disease (COPD)

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Note:

• This article is just a summary of respiratory pathophysiology.

• For further information on this topic, you can consult specialized medical literature.