Pulmonary Ventilation Lecture Notes

Introduction

• Purpose of the Respiratory System: Gas exchange, bringing materials in and out of the lungs.
• Key Concepts: How lungs remain inflated, Boyle's Law, pressure differentials in the respiratory system.

Lung Inflation

• Intrapleural Pressure:
  • Low pressure between parietal and visceral pleura (~756 mmHg or -4 mmHg relative to zero atmospheric pressure at sea level).
  • Chest wall expansion increases volume and decreases pressure due to Boyle's Law.
• Cohesion Forces:
  • Cohesion of water at pleural interfaces helps lungs move with chest wall.
  • Elastic tissues in lungs pull inward.

Pressure Dynamics

• Intrapulmonary vs. Intrapleural Pressure:
  • Intrapulmonary pressure is greater than intrapleural pressure, keeping lungs inflated.
  • Picture diagram explanation of pleural cavity as a negative pressure space.

Anatomy

• Pleura:
  • Parietal pleura (outer), visceral pleura (touching the lungs), pleural cavity in between.

Pressure Systems

• Alveolar Pressure (P_ALV):
  • Air in alveoli tries to equal atmospheric pressure (760 mmHg or zero).
  • Elastic fibers around alveoli decrease volume, increasing pressure.
• Alveolar Fluid:
  • Type I alveolar cells make fluid that helps draw alveoli together.
  • Surfactant prevents collapse by reducing surface tension.

Thoracic Mechanics

• Chest Wall and Muscles:
  • Muscles pull the chest wall outward and lungs inward, maintaining low pressure in pleural cavity.
• Pressure Imbalance and Pneumothorax:
  • Air in pleural cavity can equalize pressures, leading to atelectasis (lung collapse).
  • Small pneumothoraxes may resolve on their own; large ones need medical intervention (e.g., chest tube).

Pulmonary Ventilation

• Respiratory Process:
  • Movement of gases between atmosphere and alveoli.
  • Inspiration: air moves in due to lower pressure inside compared to atmospheric pressure.
  • Expiration: air moves out as pressure inside exceeds atmospheric pressure.

Breathing Types

• Quiet Breathing (Eupnea):
  • Rhythmic breathing at rest; no energy used in expiration.
• Forced Breathing:
  • Uses additional muscles during exercise or situations requiring strong exhalation.

Muscles of Respiration

• Inspiration Muscles: Diaphragm, external intercostals.
• Forced Inspiration: Sternocleidomastoid, scalenes, serratus posterior, pectoralis minor, erector spinae.
• Forced Expiration: Transversus thoracis, serratus posterior inferior, internal intercostals, external oblique, transverse abdominals.

Boyle's Law

• Principle: Inverse relationship between gas pressure and volume (increase volume -> decrease pressure, decrease volume -> increase pressure).

Summary

• Key Takeaway: Understanding the pressure dynamics and muscular mechanics is crucial for effective pulmonary ventilation and gas exchange.

These notes summarize the key concepts and mechanics involved in pulmonary ventilation, focusing on pressure dynamics, lung mechanics, and respiratory muscle involvement.