Respiratory Pathophysiology

1. Structure of the Respiratory System:

• Thorax:

• Consists of the spine, ribs, and sternum.

• Inpiratory Muscles:

• Normal: Diaphragm and external intercostals.

• Forced: Scalenes, sternocleidomastoid, serratus anterior (cheek, tongue, nasal wing muscles).

• The diaphragm accounts for 2/3 of the inhaled air.

• Expiratory Muscles:

• Normal: No muscles involved, no energy required.

• Forced: Internal intercostals and abdominal wall muscles.

• Airways:

• Includes the trachea, bronchi, bronchioles, and terminal bronchioles.

• Classification by structure:

• Cartilaginous Airways:

• From the trachea to the bronchioles.

• Collapsing lumen: due to secretion production by wall cells.

• Membranous Airways:

• Terminal bronchioles.

• Reissesell muscle: constricts/dilates lumen.

• Classification by function:

• Conducting Airways:

• From the trachea to the bronchioles.

• Lined with mucous membrane.

• Nourishment: bronchial arteries.

• Gas Exchange Airways:

• The end portion of terminal bronchioles, alveolar ducts, alveoli.

• Nourishment: pulmonary circulation.

• Lungs:

• 300-500 million alveoli.

• The number of alveoli depends on height and exercise.

• Alveoli surface: lining cells, surfactant-producing cells.

• Anatomical surface area: 80 m2.

• Functional surface area: 70 m2 (area used for respiration).

• Pleura:

• Consists of two layers, one cavity (containing a thin layer of fluid).

• Negative pressure within the pleural cavity is crucial for inspiration.

• When punctured, air enters –> lung collapse.

• Circulatory System:

• Nutritional system:

• Originates from the systemic circulation.

• Nourishes lung parenchyma and bronchi.

• Functional system:

• Originates from the pulmonary circulation.

• 6000-7000 liters/day.

2. Respiratory Function:

• Supply oxygen, eliminate CO2.

• 4 stages:

• Ventilation (breathing):

• Performs gas exchange between alveoli and the external environment through two actions: inhalation and exhalation.

• During inhalation: alveolar pressure < atmospheric pressure.

• During exhalation: alveolar pressure > atmospheric pressure.

• Function: renewal of air in the alveoli, maintaining stable pCO2 and pO2 in residual air.

• Diffusion:

• Passive gas exchange between alveoli and blood across the diffusion membrane.

• Dependent on:

• Pressure difference across the alveolar-blood membrane.

• Total alveolar surface area.

• Thickness of the alveolar-blood membrane.

• Solubility of each gas.

• Transport:

• Delivers O2 from lungs –> cells, carries CO2 from cells –> lungs.

• Dependent on: blood function, circulatory system.

• Exchange across cell membrane – cellular respiration:

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

• The oxygen consumption rate of the cell determines the rate of oxygen uptake into the cell.

• Cellular respiration intensity determines the level of oxygen uptake from the external environment into the body.

3. Respiratory Regulation:

• Respiratory Center: medulla oblongata, pons.

• Includes 3 groups of neurons –> 3 centers: inspiration, expiration, regulation: regulates automatic activity.

• Cerebral cortex: controls forced respiration.

4. Respiratory Function Testing:

• Spirometry:

• Ventilation capacity testing:

• 3 basic parameters: VC, FEV1, Tiffeneau index.

• Expanded parameters: FVC, TLC, RV.

• Assessing lung parenchyma function through gas exchange volume.

• Assessing airways through air flow rate.

• Diffusion capacity testing:

• Measuring blood pCO2, pO2: assessing diffusion.

• Comparing blood and alveolar pCO2, pO2 –> more accurate.

5. Ventilation Disorders:

• Classification by mechanism:

• Restrictive: decrease in the number of alveoli involved in gas exchange with the external environment.

• Anatomical decrease: lobectomy, emphysema in the elderly, lung collapse…

• Functional decrease:

• Thoracic cage damage: kyphosis, scoliosis, diaphragm paralysis, intercostal neuralgia.

• Lung parenchyma disease: pneumonia, pulmonary edema, pulmonary fibrosis.

• Functional testing:

• Decreased volume parameters.

• Decreased/normal flow rate parameters.

• Obstructive: airway narrowing –> affecting gas exchange in a large number of alveoli.

• Due to high airways: laryngeal edema, diphtheria, large foreign bodies.

• Due to cartilaginous airways: small foreign bodies.

• Due to membranous airways:

• Temporary Reissesell muscle contraction: asthma.

• Bronchial wall hypertrophy, secretion production: chronic inflammation, chronic smoke poisoning.

• Functional testing:

• Normal/decreased volume parameters.

• Decreased flow rate parameters.

6. Diffusion Disorders:

• Factors affecting the diffusion process:

• Decreased exchange membrane surface area.

• Ventilation-perfusion mismatch.

• Increased exchange membrane thickness.

• Reduced pressure gradient.

7. Chronic Obstructive Pulmonary Disease (COPD):

• Disease separation:

• Previously, COPD included 3 diseases: asthma, chronic bronchitis, emphysema.

• Since 2001, COPD, asthma, chronic bronchitis are separate diseases, but share common symptom manifestations, emphysema is a consequence.

• Causes:

• Genetics: alpha 1 deficiency, bronchial hypersensitivity to stimuli.

• External environment: smoking, dust, environmental pollution.

• There are 4 stages:

• Stage 0: chronic cough, sputum production, normal respiratory function.

• Stage 1: FEV1 >= 80%, FEV1/FVC < 70%.

• Stage 2: 30% < FEV1, 80%.

• Stage 2a: FEV1 > 50%.

• Stage 2b: FEV1 < 50%.

• Stage 3: FEV1 < 30%.

8. Respiratory Failure:

• A condition where the body cannot meet the body’s oxygen supply and CO2 elimination requirements.

• There are 3 types:

• Respiratory failure due to decreased blood oxygen when PaO2 <= 60mmHg.

• Increased blood CO2 when PaCO2 >= 50 mmHg accompanied by acidosis pH < 7.35.

• Mixed type: decreased blood oxygen and increased blood CO2.

• Classification according to:

• Severity:

• Grade I: dyspnea occurring during heavy exertion.

• Grade II: decreased pO2 during moderate exertion.

• Grade III: decreased pO2 during mild exertion.

• Grade IV: decreased arterial blood pO2 even at rest.

• Location of control and execution.

Note:

• It’s easy to confuse with heart disease, need respiratory function testing, rule out heart disease, measure arterial blood pO2.