Physical Principles of Respiratory Care

States of Matter

• Three primary states: Solids, Liquids, Gases, Plasma

  • Solids: Fixed volume & shape; high internal order; strong attractive forces.

  • Liquids: Fixed volume; adapt to container shape; weaker attractive forces than solids.

  • Gases: No fixed volume/shape; weak attractive forces; rapid, random motion.

  • Plasma: Fourth state; consists of neutral atoms and free electrons; reacts to electromagnetic forces.

Internal Energy of Matter

• Atoms in constant motion; internal energy consists of:

  • Potential Energy: Energy of position; weak in gases; predominant in solids and liquids.

  • Kinetic Energy: Energy of motion; predominant in gases.

Laws of Thermodynamics

• Study of matter behavior at various temperatures; includes:

  • Properties of temperature, energy, entropy.

  • First Law: Heat moves from hot to cool objects.

Heat Transfer

• Can occur via:

  • Conduction: Heat transfer through direct contact.

  • Convection: Mixing of fluid molecules.

  • Radiation: Transfer without contact.

  • Evaporation/Condensation: Phase change from liquid-gas and vice versa.

Temperature

• Measurement of heat related to molecular collision.

• Temperature scales: Celsius, Fahrenheit, Kelvin.

  • Absolute zero: No kinetic energy, lowest possible temperature.

Change of State

• Melting: Solid to liquid at melting point; Freezing: Liquid to solid at freezing point.

• Sublimation: Solid to gas directly (e.g., dry ice).

Properties of Liquids

• Pressure: Depends on height & density.

• Buoyancy: Pressure below exceeds above, aiding suspension.

• Viscosity: Resistance to flow; increases energy demand on the heart with elevated blood viscosity.

Surface Tension and Laplace’s Law

• Surface tension: Force that keeps liquid surface intact.

• Laplace’s Law: Pressure inside a bubble is inversely proportional to its radius.

• Surfactants prevent smaller alveoli from emptying into larger ones, maintaining alveolar stability.

Gas Laws

• Boyle’s Law: Volume and pressure vary inversely at constant temperature.

• Charles’ Law: Volume and temperature vary directly at constant pressure.

• Gay-Lussac’s Law: Pressure and temperature vary directly at constant volume.

• Graham’s Law: Rate of gas diffusion is inversely proportional to the square root of its density.

• Dalton’s Law: Total pressure in a gas mixture equals the sum of individual partial pressures.

• Henry’s Law: Gas solubility in a liquid is proportional to the gas pressure above the liquid.

Fluid Dynamics

• Study of fluids in motion; affected by flow patterns:

  • Laminar: Smooth flow in layers.

  • Turbulent: Chaotic flow.

• Bernoulli Principle: Increase in fluid velocity leads to decrease in pressure.