RGI 3 Gas laws - clinical relevance, gas pressures within the body

Section 1: Boyle's Law & Charles' Law

Boyle’s Law

  • Definition: For a fixed mass of enclosed gas at constant temperature, the product of pressure (P) and volume (V) remains constant (P × V = constant).

    • Equation: P1V1 = P2V2

  • Significance: Essential for understanding pressure changes during respiration.

Charles’ Law

  • Definition: For a fixed mass of enclosed gas at constant pressure, the ratio of volume to temperature is constant.

    • Equation: V1/T1 = V2/T2

  • Key Concept: Volume increases as temperature increases, relevant in the context of gas behavior during respiration.

Section 2: Ideal Gas Law

  • Combines Boyle’s and Charles’ laws into a single equation: PV = nRT

    • Where: n = number of molecules, R = universal gas constant (8.314 J mol^-1 K^-1)

  • Implication: Temperature must be expressed in Kelvin (T(K) = °C + 273).

  • Temperature and Pressure Relationship: Lower temperatures lead to decreased gas pressure.

    • Example: Demonstrated with a steel drum crush simulation.

  • In a fridge heat pumps work by slowly compressing a closed volume of refrigerant gas and then rapidly removing pressure which cools the Gas.

  • The Gauge pressure effect

  • P=pgh is negligible in gases all gas at equilibrium are the same pressure.

Section 3: Dalton’s Law of Partial Pressures & Henry’s Law of Gas Solubility

Dalton’s Law

  • Definition: Total pressure of a gas mixture equals the sum of the partial pressures of individual gases.

  • Implication: Each gas behaves independently in a mixture.

Henry’s Law

  • Definition: Concentration of a gas in a liquid is proportional to the partial pressure of that gas above the liquid (explains carbonation of drinks). ( solubility)

  • Applications: Relevant in contexts like decompression sickness and ultrasonic cavitation.

  • Relevant in ultrasonic Cavitation Which is used to vaporise tumor tissue.

Section 4: Laplace's Law

  • Definition: Relates the tension in a membrane to the pressure difference on either side.

    • Equation: AP = 2T/R where T is wall tension and R is radius.

  • Application: Essential for understanding pressure changes during respiration in alveoli.

Section 5: Respiration & Gas Laws

  • Anatomy Involved: Intercostal muscles, diaphragm, alveoli, and trachea.

  • Alveoli Characteristics: ~300 million alveoli provide a vast surface area (~80 m²) for gas exchange.

  • Volume and pressure within the pleural space is controlled by action of the diagram and Boyles law

    • During inspiration the diaphragm moves down, intercostal muscles move out= the pleural volume increases, causing t the plural pressure to decrease.

    • The drop in the pressure of the intrapulmonary space increases in the change of pressure on the aveolar wall. higher radius increases tension. ( the alveolus expands allowing for the atmosphere to rush in)

    • During expiration diaphragm and intercostals relax so the plural pressure increases while the plurale volume decreses. Breath is pushed out passively.

  • Intra-Pleural Pressure: Behavior of pressures during inspiration and expiration involves Boyle’s Law; volume increases during inspiration leading to decreased pressure, allowing air influx.

  • Respiration Mechanics: During expiration, pressure increases as the diaphragm and intercostals relax, pushing air out passively.

Section 6: Respiratory Measurements & Viscous Properties of Air

  • Typical Flow Rates: Comparison of normal flow vs. patients with airway constriction (like asthma).

  • P-V Curves: Demonstrate implications of airflow and lung volume relationship for normal vs. abnormal respiration.

  • Poiseuille’s Law: Provides insight into the influence of airway diameter on resistance and airflow; critical in conditions like asthma.