Pulmonary Ventilation Overview

Introduction

• Pulmonary ventilation involves tricking air into entering and exiting the body by changing pressures.
• Breathing is a two-phase process:
  • Inspiration (Inhalation)
  • Expiration (Exhalation)

Role of the Diaphragm

• The diaphragm is a crucial muscle for breathing, located between the thoracic and abdominal cavities.
• Controlled by the phrenic nerve.
• Contracts to facilitate breathing by changing thoracic pressure.

Inspiration

• Active Process: Requires muscle effort.
• Boyle's Law: Increase in volume leads to a decrease in pressure.
  • Thoracic Expansion: Ribs and diaphragm work to increase thoracic volume.
  • Air moves from high pressure to low pressure, entering the lungs.
• Forced Inspiration: Utilizes additional muscles (e.g., pectorals, sternocleidomastoid) for deeper inhalation.

Surfactant

• Surfactant prevents alveoli from collapsing by reducing surface tension.
• Especially important in premature babies to prevent respiratory distress syndrome.

Expiration

• Passive Process: Does not require energy (ATP).
• Involves relaxing muscles and allowing elastic recoil of lung tissues.
• Forced Expiration: Uses muscles like internal intercostals and abdominals to expel more air.

Ventilation Mechanics

1. Inspiration: Muscle contraction increases thoracic volume, decreases pressure, air flows in.
2. Expiration: Thorax relaxes, decreases volume, increases pressure, air flows out.

Respiratory Volumes

• Tidal Volume: Normal breathing volume (~500 mL).
• Inspiratory Reserve Volume: Extra air inhaled after normal inspiration.
• Expiratory Reserve Volume: Extra air exhaled after normal expiration.
• Residual Volume: Air remaining after maximum exhalation.
• Vital Capacity: Total usable air capacity (important for assessing lung health).
• Total Lung Capacity: Sum of vital capacity and residual volume.

Reflexive Respiratory Actions

• Coughing: Clears lower respiratory tract.
• Sneezing: Clears upper respiratory tract.
• Laughing/Crying: Short air bursts.
• Hiccup: Diaphragm spasm.
• Yawning: May serve to increase alertness and inflate alveoli.

Breathing Control

• Essential for homeostasis; managed involuntarily by the brain.
• Main goal is expelling CO2 to prevent blood acidity.
• Carbon Dioxide and pH Balance:
  • CO2 forms carbonic acid in blood, releasing hydrogen ions.
  • Imbalance leads to acidosis or alkalosis.
• Maintaining pH balance is crucial for proper bodily function.

Conclusion

• Understanding pulmonary ventilation helps in appreciating the mechanics of breathing and maintaining respiratory health.