Pulmonary Ventilation and Breathing

Key Concepts

• Pulmonary Ventilation: The process of air flowing in and out of the lungs during inspiration (inhaling) and expiration (exhaling).
• Gas Laws:
  • Air flows from higher to lower pressure.
  • Pressure increases when volume decreases and vice versa.
  • Volume of gas increases with increased temperature.

Pressures Involved

• Intrapulmonary Pressure: Equals atmospheric pressure at rest.
• Intrapleural Pressure: Normally negative, acts as suction to keep lungs inflated.
  • Pneumothorax: When intrapleural pressure equals atmospheric pressure, leading to lung collapse.

Mechanism of Breathing

• Inspiration:

  • Diaphragm and intercostal muscles contract.
  • Thoracic cavity expands, reducing pressure and drawing in air.
  • Warming of inhaled air increases volume, aiding lung inflation.

• Expiration:

  • Quiet Expiration: Passive, relies on lung elasticity.
  • Deep Expiration: Active, requires forceful muscle contractions.

Factors Affecting Ventilation

• Lung Compliance: Ease of lung expansion.

  • High compliance: Lungs easy to inflate (like a thin balloon).
  • Low compliance: Lungs are stiff (like a thick balloon), seen in fibrosis.

• Airflow Resistance:

  • Increased by airway narrowing (e.g., asthma).
  • Bronchioles:
    • Constriction: Increased resistance (parasympathetic stimulation, histamine).
    • Dilation: Decreased resistance (epinephrine).

Health Implications

• Conditions like emphysema reduce lung elasticity, making exhalation difficult.
• Diseases causing airway narrowing lead to increased resistance and difficulty breathing.

Summary

• Pulmonary ventilation is a highly regulated process influenced by muscle activity, air pressure differences, airway resistance, and lung compliance. Understanding these mechanisms is crucial for diagnosing and managing respiratory diseases.