Physical Principles of Respiratory Care

Physical Principles of Respiratory CareEgan Chapter 6 1Physical Principles of Respiratory CareStates of MatterChange of StateGas Behavior Under Changing ConditionsFluid DynamicsIII. Gas Behavior Under Changing ConditionsGas LawsEffect of Water VaporCorrected Pressure ComputationsCorrection FactorsProperties of Gases at Extremes of Temperature and PressureCritical Temperature and Pressure3A. Gas LawsBoyles LawCharles LawGay-Lussacs LawBoyles Law

Robert Boyle1627-1691British chemistPressure-volume relationship5Boyles Law6If temperature (T) remains constant, pressure (P) will vary inversely to volume (V)P1V1 = P2V2

Boyles Law7If temperature (T) remains constant, pressure (P) will vary inversely to volume (V)

If gas P , the V occupied by the gas

If gas V , the P exerted by the gas Boyles Law8

PTV

Ventilation is an example of Boyles LawAs the diaphragm drops at the beginning of inspirationThe volume of the lungs increasesAs lung volume increases what happens to the pressure inside the lungs?It _________And air flows into the lungshttp://www.youtube.com/watch?v=q6-oyxnkZC0

9Boyles Law10A snorkel diver is preparing to descend a freshwater pond to a depth of 66 feet. At sea level, his lungs contain about 3000 mL of air. As he descends below the surface of the water, what will happen to the gas volume in his lungs as he descends to 66 feet below the surface of the pond?P1V1 = P2V2P1V1 = V2 P233.9 ftH2O x 3000 mL = V2 99.9 ftH2O101700 mL = V2 = 1018 mL99.9

Charles Law

Jacques Charles1746-1823French chemistVolume-temperature relationship11Charles Law12If pressure (P) remains constant, the volume (V) will vary directly with temperature (T)V1 = V2T1 T2

Charles Law13If pressure (P) remains constant, the volume (V) will vary directly with temperature (T)

If gas T , the V occupied by the gas also As T , kinetic energy , the gas molecules move more vigorously and the gas expands

If gas T , the V occupied by the gas also As T , kinetic energy , the gas molecules slow down and the gas contractsTire volume is an example of Charles Law14

Gay-Lussacs Law15An oxygen cylinder has a pressure of 2200 psi at a temperature of 25 C, what will its pressure be if it is heated to 50 C? (Must first convert temperature to Kelvin)P1 = P2T1 T2P1 T2 = P2 T1P1 T2 = P2 T12200 psi x 323 K = P2 298 K710600 psi = P2 2982384 psi

Gay-Lussacs Law

Joseph Gay-Lussac1778-1850Expanded on Charles workPressure-temperature relationship16Gay-Lussacs Law17If volume (V) remains constant, pressure (P) will vary directly with temperature (T)P1 = P2T1 T2

Gay-Lussacs Law18If volume (V) remains constant, pressure (P) will vary directly with temperature (T)

If gas T , the P exerted by the gas also

If gas T , the P exerted by the gas also Gas Cylinder Pressures and Temp is an example of Gay-Lussacs LawAn alarm signals that there is a fire in the basement of the hospital. Although the fire is confined to an area that is approximately 300 feet from the room where the compressed-gas cylinders are stored, you are asked to move the cylinders to a safer location. Why is it necessary to move the cylinders?

Keep cylinder temperature below 125F (51.7C)http://www.youtube.com/watch?v=xceBXe5YHj0

19Charles Law20Given: 100 mL of an unknown gas measured at 28 C and 760 mmHg. Find the gas volume measured at 37 C and 760 mmHg.(Must first convert temperature to Kelvin)V1 = V2T1 T2V1T2 = V2 T1V1T2 = V2 T1100 mL x 310 K = V2 301 K31000 mL = V2 301= 103 mL

III. Gas Behavior Under Changing ConditionsGas LawsEffect of Water VaporIn clinical practice, most gas law calculations must take into account the presence of water vapor. Water vapor, similar to any gas, occupies space. The dry volume of a gas at a constant pressure and temperature is always smaller than its saturated volume. The opposite is also true. Correcting from the dry state to the saturated state always yields a larger gas volume.The addition of water vapor to a gas mixture always lowers the partial pressures of the other gases present. This fact becomes relevant when discussing the partial pressure of gases in the lung where the gases are saturated with water vapor at body temperature.21III. Gas Behavior Under Changing ConditionsGas LawsEffect of Water VaporThe addition of water vapor to a gas mixture always lowers the partial pressures of the other gases present. This fact becomes relevant when discussing the partial pressure of gases in the lung where the gases are saturated with water vapor at body temperature.22III. Gas Behavior Under Changing ConditionsGas LawsEffect of Water VaporCorrected Pressure ComputationsPC = (PT PH20)23III. Gas Behavior Under Changing ConditionsGas LawsEffect of Water VaporCorrection FactorsCorrection from ATPS to BTPSCorrection from ATPS to STPDCorrection from STPD to BTPS24Table 6-3

Clinical Example: Spirometry26Spirometry: laboratory evaluation of lung function using a spirometerSpirometer: a device for measuring lung volumes and/or flowsWhen a patient exhales into a spirometer the gas is measured at room temperatureAbout 25CATPS: Ambient Temperature Pressure SaturatedBut inside the lungs the gas is at body temperatureAbout 37CBTPS: Body Temperature Pressure Saturated

Clinical Example: Spirometry27As the patient exhales and the temperature of the gas decreases to room temperature

What will happen to the volume of gas?

Whose law tells us this?It will DECREASE

III. Gas Behavior Under Changing ConditionsGas LawsProperties of Gases at Extremes of Temperature and PressureSee Mini Clini: Variations from Ideal Gas Behavior: Expansion Cooling and Adiabatic Compression page 121.28III. Gas Behavior Under Changing ConditionsGas LawsCritical Temperature and PressureCritical temperature: the highest temperature at which a substance can exist as a liquid. The temperature above which the kinetic activity of its molecules is so great that the attractive forces cannot keep them in a liquid state. Critical pressure: the pressure needed to maintain equilibrium between the liquid and gas phases of a substance at this critical temperature.Together, the critical temperature and pressure represent the critical point of a substance.292. Critical Temperature and PressureLiquid oxygen is produced by separating it from a liquefied air mixture at a temperature below its boiling point (183C or 297F). After it is separated from air, the oxygen must be maintained as a liquid by being stored in insulated containers below its boiling point (-183 C)If higher temperatures are needed, higher pressures must be used. If at any time the liquid oxygen exceeds its critical temperature of 118.8C, it converts immediately to a gas.