In-Depth Notes on Respiratory Physiology - Gas Exchange lecture bite 2

Gas Exchange Overview

• Definition: Gas exchange is the process of delivering oxygen from the lungs to the bloodstream and eliminating carbon dioxide from the bloodstream to the lungs.

Learning Outcomes

• Identify gas changes and physiological changes that influence gas exchange rate.
• Describe the effect of partial pressures on gas flow using:
  • Henry’s Law: Quantity of gas that will dissolve in a liquid is proportional to the partial pressure of the gas.
  • Boyle’s Law: Volume change in a gas container causes an inverse pressure change: P1 V1 = P2 V2 .
  • Dalton’s Law: Total pressure of a gas mixture equals the sum of the individual gas pressures.
• Explain the role of hemoglobin in O2 and CO2 transport, considering:
  • Effect of pH
  • CO2 levels
  • Partial pressure of O2 (PO2)
• Differences in gas binding between:
  • Maternal & fetal hemoglobin
  • Hemoglobin & myoglobin
• Use gas laws & mechanisms to explain:
  • Signs of high altitude, mountain sickness, hypoxia
  • Carbon monoxide poisoning

Factors Affecting Gas Exchange

• Oxygen Reaching the Alveoli:
  • Concentration of inspired air
  • Alveolar ventilation
  • Rate & depth of breathing
  • Airway resistance
  • Lung compliance
• Gas Diffusion Factors:
  • Surface area available for diffusion
  • Diffusion distance
  • Barrier thickness
  • Adequate perfusion of alveoli
  • Amount of fluid in the alveoli

Laws Affecting Gas Composition

• Henry’s Law: C = k_H imes P
  • Where C = concentration of gas in liquid, $k_H$ = Henry's law constant, and P = partial pressure of gas.
• Boyle’s Law: P1 V1 = P2 V2
  • Inverse relationship between pressure and volume.
• Dalton’s Law: Total pressure equals the sum of partial pressures of individual gases.

Pressures and Partial Pressures

• Partial Pressure: The pressure exerted by a specific gas in a mixture of gases.
  • Example: Air composition includes CO2, O2, and N2.

Partial Pressure Calculations

• Example Calculation: Air pressure = 760 mmHg, O2 is 20% of air.
  1. Convert 20% to decimal: 20/100 = 0.2
  2. Calculate PO2:
  • PO2 = 0.2 imes 760 ext{mmHg}
  • PO2 = 152 ext{mmHg}

Summary

• Understanding gas exchange involves physiological mechanisms, the laws of gas behavior, and their application in medical contexts.