Altered Ventilation and Diffusion

Chapter Overview: Altered Ventilation and Diffusion

• Overview of respiratory system functions including ventilation and diffusion.

Objectives

• Understand pathogenesis of common infectious and inflammatory lung disorders.
• Differentiate between mechanisms causing disorders of ventilation and diffusion.
• Discuss major respiratory disorders, including respiratory failure.

Respiratory Structures

• Nasopharynx, nasal cavity, oropharynx, epiglottis, laryngeal pharynx, and esophagus play roles in air conduction.
• Pleural membranes: visceral and parietal pleura.
• Lung lobes: upper and lower lobes of both right and left lungs.
• Bronchial structure: right main bronchus, left main bronchus, bronchioles, and alveoli.
• Role of pulmonary vessels: pulmonary artery delivers blood, pulmonary veins return oxygenated blood.
• Components of alveoli including surfactant and alveolar macrophages which aid in gas exchange.

Ventilation Mechanics

• Inspiration:

  • Process of inhaling to acquire oxygen.
  • Air moves from high pressure to low pressure; pressure gradient driven by chest cavity expansion.

• Expiration:

  • Removal of carbon dioxide through the relaxation of diaphragm and intercostal muscles.
  • Increased internal pressure compresses lungs.

• Measurement:

  • Tidal volume (TV), vital capacity (VC), forced vital capacity (FVC), forced expiratory volume in 1 second (FEV1), residual volume (RV), and total lung capacity (TLC).

Diffusion of Gases

• Exchange of oxygen and carbon dioxide occurs at alveolar capillary junctions.
• Key factors affecting diffusion:
  • Partial pressure and solubility of the gases.
  • Membrane thickness and surface area.

Partial Pressure

• Defining partial pressures:
  • Partial pressure of oxygen (PaO2) and carbon dioxide (PaCO2) as measurable values in mm Hg.

Carbon Dioxide Transport

• CO2 transported via plasma, bound to hemoglobin, and converted to bicarbonate in red blood cells.
• Exhaled through lungs.

Impaired Ventilation

• A blockage or disruption of airflow at the lungs.
  • Mechanisms:
    • Compression or narrowing of airways.
    • Disruption of neuronal control of breathing.
  • Consequences include hypoxemia, hypoxia, and hypercapnia.

Altered Diffusion

• Impairment in oxygen or carbon dioxide transfer across alveolar-capillary membrane.
  • Factors include surface area, membrane thickness, and gas pressures.
  • Results in hypoxemia and hypercapnia.

General Manifestations of Impaired Ventilation and Diffusion

• Symptoms include cough, dyspnea, use of accessory muscles, and chest pain. May lead to barrel chest appearance.

Diagnostic Testing

• Tools: pulmonary function tests, arterial blood gases, imaging (x-ray, CT, MRI), and cultures.

Treatment Strategies

• Focus on restoring airflow and gas exchange:
  • Remove obstructions, restore chest wall integrity, decrease inflammation and mucus, provide supplemental oxygen, and use mechanical ventilation when necessary.

Clinical Models of Respiratory Disorders

• Common conditions: pneumonia, COPD (emphysema and chronic bronchitis), asthma, and acute respiratory distress syndrome (ARDS).

Asthma

• Pathophysiology: Intermittent airway obstruction due to bronchial hyperresponsiveness and inflammation.
• Clinical Manifestations: Wheezing, dyspnea, coughing, chest tightness.
• Diagnostics: History, pulmonary function testing, x-rays.
• Treatment: Monitor function, control triggers, pharmacotherapy.

Emphysema

• Pathophysiology: Irreversible lung tissue destruction, primarily due to smoking.
• Clinical Manifestations: Persistent cough, wheezing, barrel chest, dyspnea.
• Diagnostics: Similar to asthma with pulmonary function tests and imaging.
• Treatment: Smoking cessation, pharmacotherapy, lung volume reduction.

Chronic Bronchitis

• Pathophysiology: Chronic productive cough resulting from airway inflammation.
• Clinical Manifestations: Productive cough with purulent sputum, cyanosis, and dyspnea.
• Diagnostics: Similar to emphysema; emphasis on sputum analysis.
• Treatment: Smoking cessation, pulmonary rehabilitation, mucolytics.

Pneumonia

• Pathophysiology: Infectious process from respiratory droplets causing lung inflammation.
• Clinical Manifestations: Fever, cough, dyspnea, pleuritic pain.
• Diagnostics: Blood tests, imaging for consolidation.
• Treatment: Identify pathogen, provide supplemental oxygen.

Cystic Fibrosis (CF)

• Pathophysiology: Autosomal recessive disorder affecting pulmonary function and causing mucous obstruction.
• Clinical Manifestations: Chronic infections, cough, respiratory distress.
• Diagnostics: Sweat test, sputum analysis.
• Treatment: Chest physiotherapy, nutritional support, lung transplant.

Acute Respiratory Distress Syndrome (ARDS)

• Pathophysiology: Rapid progression from lung injury to distress; severe inflammation and pulmonary edema.
• Clinical Manifestations: Dyspnea, anxiety, retractions, crackles.
• Diagnostics: Blood gas measurements, imaging studies.
• Treatment: Removal of causative factors, use of mechanical ventilation, oxygen administration.