Physical Principles of Respiratory Care

Physical Principles of Respiratory Care

• The presentation covers physical principles relevant to respiratory care.
• Objectives include describing states of matter, changes of state, and gas behavior.
• Objectives also include understanding water vapor capacity, absolute humidity, and relative humidity.
• Objectives include predicting gas behavior under changing conditions.

States of Matter

• Three primary states of matter: solids, liquids, and gases.
• Solids have a high degree of internal order, fixed volume and shape, and strong mutual attractive forces between atoms.
• Liquids have a fixed volume but adapt to the shape of their container; atoms exhibit less mutual attraction compared with solids.
• Gases have no fixed volume or shape; molecules exhibit rapid, random motion with frequent collisions.

Internal Energy of Matter

• Atoms in matter are constantly in motion at normal temperatures.
• Internal energy is the source of this motion.
• Internal energy includes potential energy (energy of position) and kinetic energy (energy of motion).
• Potential energy is stronger in solids and liquids, while kinetic energy is prominent in gases.

Laws of Thermodynamics

• Thermodynamics is the study of matter properties and reaction rates at various temperatures.
• Energy cannot be created or destroyed, only transferred.
• The first law of thermodynamics involves heat transfer between objects at different temperatures. Heat flows from hotter to cooler objects until both reach an equal temperature.
• Heat transfer can occur through four mechanisms: conduction (direct contact), convection (fluid movement), radiation (no direct contact), and evaporation/condensation (change of state).

Properties of Liquids

• Archimedes' Principle: An upward force on a submerged object is equal to the weight of the fluid displaced.
• Buoyancy is influenced by pressure difference below and above a submerged object.
• Viscosity: the resistance to fluid flow, directly proportional to cohesive forces between molecules.
• Blood has a higher viscosity than water.
• Cohesion: attraction between molecules of the same substance.
• Adhesion: attraction between molecules of different substances.
• Surface tension: force exerted by like molecules at a liquid's surface.
• Surface tension helps maintain spherical shapes of bubbles.
• Capillary action: upward movement of liquid in a narrow tube against gravity; influenced by adhesion and surface tension.
• Liquids are subject to Pascal's Principle, where pressure depends on liquid height and density, not the shape of the container.

Fluid Dynamics

• Fluid dynamics is the study of fluids in motion.
• Fluid pressure in motion depends on the nature of the flow.
• Flow resistance is the opposition to fluid flow.
• Progressive decrease in pressure occurs as fluid flows through a tube due to resistance. Factors include fluid density, viscosity, linear velocity, and tube radius.
• Bernoulli Principle: Velocity increases and lateral pressure decreases as a fluid flows through a constriction.
• Fluid entrainment: Negative pressure due to high velocity can pull another fluid into the primary flow stream.
• Venturi masks use the principle of reduced pressure to entrain gases (typically air) into a low pressure area.

Patterns of Flow

• Laminar flow: fluids move in parallel layers, no disruption between layers.
• Turbulent flow: chaotic flow, with high pressure and property changes.
• Transitional flow: mixture of laminar and turbulent flow.

Properties of Gases

• Gases exhibit considerable kinetic activity, with molecules moving randomly and colliding frequently.
• Gas velocity is proportional to temperature.
• Ideal molar volume is 22.4 L at standard temperature and pressure (STP).
• Gas density is the ratio of gas mass to volume.
• Gaseous diffusion is the movement of molecules from high-concentration areas to low-concentration areas (Graham's Law).
• Gas pressure is exerted by gas molecules.
• Gas tension is gas pressure in liquid solutions.
• Gravity affects gas pressure and density, influencing molecular collisions and tension.
• Pressure decreases with increasing altitude.

Change of State

• Melting: solid to liquid transition. Melting point is the temperature of this change.
• Freezing: liquid to solid transition.
• Sublimation: solid to gas transition, without becoming a liquid first.
• Evaporation: liquid converting to gas at temperatures below the boiling point, based on vapor pressure exceeding atmospheric pressure.
• Condensation: Opposite of evaporation; gas to liquid transition.

Water Vapor Capacity, Absolute Humidity, and Relative Humidity

• Water vapor capacity: amount of water vapor air can hold.
• Absolute humidity: actual amount of water vapor in the air.
• Relative humidity: ratio of absolute humidity to water vapor capacity at a given temperature, expressed in percent.

Temperature

• Temperature is a measurement of heat, closely related to kinetic energy—the energy of motion of particles.
• Heat is produced by molecular collisions.
• Gas temperature is directly proportional to kinetic energy of molecules.
• Solids and liquids have only some of their energy devoted to motion, and temperature represents only part of their total internal energy. Temperature scales include Fahrenheit, Celsius, and Kelvin.
• Conversion formulas exist between these scales.

Additional topics

• Air pressure, Dalton's law, Henry's law, Boyle's law, Charles' law, Gay-Lussac's law are discussed to provide a complete picture of gas behavior and properties.
• The presentation includes a mini-clinic on oxygen masks on airplanes. A detailed analysis of cabin pressure and oxygen levels, along with calculations, is included to illustrate real-world applications of these principles.