Gas Laws and Respiratory Therapy

• Matter exists in three states: solid, liquid, and gas.
• Solids have a fixed volume and shape due to strong attractive forces, and molecules move with a "jiggle" motion.
• Liquids have a fixed volume but take the shape of their container, with weaker molecular attraction than solids.
• Gases have no fixed shape or volume, exhibiting weak attractive forces and free-moving, frequently colliding molecules.

Internal Energy

• Kinetic energy is the energy of motion, predominating in gases.
• Potential energy is the energy of position, prevailing in solids and liquids.
• All matter possesses internal energy, crucial for lung mechanics and cardiac function.

Thermodynamics

• Thermodynamics involves the study of matter's properties and kinetic reactions at varying temperatures.
• Heat transfer occurs through conduction (direct contact), convection (movement in liquids/gases), radiation (no direct contact), and evaporation/condensation (phase changes).
• Conduction example: warm blankets on skin.
• Convection example: forced air heating.
• Radiation example: sun warming earth.
• Evaporation & Condensation example: sweating cools the skin

Temperature

• Kinetic energy and temperature are directly proportional.
• Absolute zero is the theoretical point where molecular motion ceases.
• Temperature is measured using Celsius, Fahrenheit, and Kelvin scales.
• Formula: F = 32 + (C * 1.8)
• Formula: C = (F - 32) / 1.8
• Formula: K = C + 273

Phase Changes

• Melting and freezing represent solid-liquid transitions at the melting point.
• Sublimation is when a solid converts directly into vapor; example dry ice.
• Boiling point is the temperature at which vapor pressure equals atmospheric pressure.
• Evaporation and condensation are critical for humidity management in respiratory care.

Liquid Properties

• Buoyancy is the upward force exerted by a fluid (Archimedes’ Principle).
• Pressure in a confined liquid is transmitted equally in all directions (Pascal’s Principle).
• Viscosity is resistance to flow; blood viscosity is 5x greater than water.
• Surface tension: Higher surface tension requires more pressure to keep alveoli open (Laplace’s Law), which is key in ARDS and surfactant use.
• Capillary action enables fluid movement against gravity, as seen in humidifiers and blood sampling.

Gas Properties

• Kinetic Theory states that gas molecules move randomly at high speeds, and collisions generate pressure.
• Density is the mass-to-volume ratio; Helium is low-density and aids airflow in airway obstructions.
• Boyle’s Law: Pressure & volume are inversely related at constant temperature (e.g., breathing mechanics).
• Charles’ Law: Temperature & volume are directly related at constant pressure (e.g., heated gas expands).
• Dalton’s Law: Total pressure of a gas mix equals the sum of partial pressures (important in oxygen therapy).
• Henry’s Law: Gas solubility in liquid is proportional to its partial pressure (e.g., oxygen in blood).
• Graham’s Law: Lighter gases diffuse faster than heavier ones.

Fluid Dynamics

• Laminar flow is smooth, organized movement (described by Poiseuille’s Law).
• Turbulent flow is chaotic movement, occurring at high velocity or in irregular passages.
• Bernoulli’s Principle: Increased velocity decreases pressure, the basis for jet nebulizers & Venturi masks.
• Jet entrainment uses shearing forces to mix room air with oxygen.
• Coanda effect: Fluid follows curved surfaces, used in mechanical ventilation.

Gas Behavior Under Changing Conditions

• Water vapor pressure must be accounted for in gas law calculations.
• Critical temperature: Above this temperature, a substance cannot exist as a liquid, even under pressure.
• Hyperbaric pressures are used for CO poisoning & wound healing.

Key Equations and Concepts

• Relative Humidity (RH) = (AH / Saturated Capacity) x 100
• Alveolar Air Equation: Used to assess oxygen delivery efficiency in the lungs.
• Altitude's Impact: Lower atmospheric pressure decreases partial pressure of oxygen, causing hypoxia at high elevations.

Clinical Applications

• Ventilation mechanics are related to Boyle’s Law.
• Humidity & airway management involve evaporation and condensation.
• Hyperbaric oxygen therapy relates to Dalton’s & Henry’s Laws.
• Oxygen therapy for airway obstruction uses helium-oxygen mixtures.
• Mechanical ventilation principles involve fluid dynamics & Bernoulli’s Principle.

Explore gas laws and their application in respiratory therapy. Understand diffusion rates, mechanical ventilation, and oxygen therapy. Learn about the clinical benefits of hyperbaric oxygen.