Respiratory Therapy - Key Terms and Definitions

Flashcards on Conditions of Measurement and Thermodynamics

STPD

Standard Temperature and Pressure, dry. Volume of gas at 0°C, at 760 mm Hg, without water vapor.

BTPS

Body temperature (37°C), barometric pressure (760 mm Hg), and saturated with water vapor.

ATPD

Ambient temperature, pressure dry

ATPS

Ambient temperature and pressure, saturated with water vapor.

First Law of Thermodynamics

Energy cannot be created or destroyed, only converted from one form to another.

Second Law of Thermodynamics

As energy changes form, entropy increases in a closed system to achieve the lowest possible energy state.

Third Law of Thermodynamics

At absolute zero all processes cease, and entropy is at a minimum value.

Conduction

Transfer of heat by direct contact between hot and cold molecules.

Convection

Mixing of fluid molecules at different temperatures.

Radiation

Radiant heat transfer without physical contact.

Evaporation

Heat is taken from the air surrounding the liquid, cooling the air.

Condensation

Heat is given back to air surrounding the liquid, warming the air.

Melting

Changeover from the solid to liquid state.

Melting Point

Temperature at which melting occurs.

Latent Heat of Fusion

Extra heat needed to change to a liquid.

Latent Heat

Calories required to change 1 g of a solid to a liquid.

Freezing

Heat energy is transferred from a liquid back to the environment, usually by exposure to cold.

Sublimation

Transition from a solid to a vapor without becoming a liquid.

Vaporization

Change of state from liquid to gas; requires heat energy.

Boiling Point

Temperature at which vapor pressure exceeds atmospheric pressure.

Evaporation (Liquid-Vapor)

A liquid changes into a gas at temperatures lower than its boiling point.

Water Vapor Pressure

The pressure exerted by water vapor.

Humidity

Water in the gaseous state, amount of water vapor in the atmosphere.

Absolute Humidity

Actual amount or weight of water vapor in air.

Relative Humidity

Ratio of actual water vapor content to saturated capacity at a given temperature.

Body Humidity

Ratio of actual water vapor content to water vapor capacity in saturated gas at body temperature (37°C).

Humidity Deficit

Amount of water vapor the body must add to inspired gas to achieve saturation at body temperature (37°C).

Dew Point

Temperature at which condensation begins.

Pascal's Principle

Pressure of a liquid acts equal in all directions.

Buoyancy

Liquids exert an upward force on submerged objects.

Surface Tension

Force exerted by like molecules at a liquid’s surface.

Pulmonary Surfactant

Substance in lungs which helps maintain surface tension.

Airway Resistance (RAW)

Resistance to ventilation by movement of gas through the airways.

Lung Compliance

Result of tissue elastic forces and surface tension.

Laminar Flow

A fluid moves in discrete cylindrical layers or streamlines.

Poiseuille's Law

Difference in pressure required to produce a given flow under laminar flow.

Turbulent Flow

Irregular eddy currents are formed in disorganized chaotic patterns.

Transitional Flow

A mixture of both laminar and turbulent flow.