GAS PHYSICS FOR RESPIRATORY THERAPY

LEARNING OBJECTIVES

Metric System 1. Understand Metric system and use by respiratory therapy. 2. Convert a unit of measure in one system to the unit in another system. 3. What are the three common temperature scales and convert between them? 4. Understand scientific notation method of numeration, exponants and mathematical operations involved with algebra in respiratory therapy.

Gas Physics 1. What are the three physical states of matter? Summarize the properties of each of these states. How are they similar and how are they different? The 3 states of matter are: solid, liquid, gas Properties of each state: solid - has strong intermolecular forces which maintain its volume and shape - has the least amount of kinetic energy of the 3 states liquid - has more kinetic energy and weaker intermolecular forces than solids which allow for movement but maintain volume -particles slide past each other = fluidity gas - has the greatest amount of kinetic energy and very weak, if any, cohesive forces between its particles - random movement of particles cause the gas to fill the available space Both solids and liquids are incompressible or nearly incompressible, meaning great pressure is needed to make either state fit into a smaller volume Both liquids and gases are fluids, meaning their constituent particles more freely and can flow

2. Explain how substances undergo change of state. What factors influence vaporization of water?

3. What is the difference between kinetic and potential energy? Kinetic energy is the energy a body possesses by virtue of its motion. Potential energy is the energy a body possesses by virtue of its position.

4. In your own words, what are the main points of the kinetic gas theory? What kind of physical phenomena is explained with this theory? The main points of the kinetic gas theory are that they (the gas particles) are far apart and they are all very small compared to the space between them. The gas particles move in rapid, random and in a straight line. Also they have very little attractive force between them. The molecules collide and exert force. The temperature determines their kinetic energy.

1 5. What four gases make up 99% of the atmosphere? 6. What is meant by “the pressure of the atmosphere”? What causes this pressure? How do we measure atmospheric pressure? "The pressure of the atmosphere" means the force of the atmospheric gases such as nitrogen, oxygen, argon, carbon dioxide and rare gases (neon, helium, krypton, methane) exert on objects within the earth's atmosphere. This pressure is much like gravity. The atmospheric gases are attracted to the earth's surface by gravity and that forms a column of air around the earth. This imaginary column of air places a weight or pressure on us on the surface of the earth. We measure atmospheric pressure with a barometer.

7. At conditions of constant temperature and pressure, the volume of a sample of ideal gas is directly proportional to the number of moles of gas present is whose law? Avagadro’s Law – states that 1 mole of gas each contains 6.02 x 1023molecules and occupies 22.4 liters.

8. What is density? How do you calculate the density of a gas? Density is comparing how much it weighs to how big it is. A very heavy object in a small space is dense. Density is calculated by mass divided by its volume. (Avagadro’s law helps us calculate gas density by using the molecular weight from the periodic table divided by 22.4 liters.

9. Predict gas behavior in changing situations (increased pressure or temperature). Gases act very predictably according to laws laid out by previous scientific discoveries. Generally they are called laws named after the scientist who first explained them i.e. Boyle, Charles, Guy-Lussac and Dalton.

10. According to Boyle’s Law, how are pressure and volume related? What is the mathematical expression that summarizes the law? In Boyles’s law volume and pressure are inversely related. When volume increases, pressure decreases and vice versa Boyle’s Law is V1 x P1 = V2 x P2

11. State Charles Law. What is the mathematical summary? The volume and temperature of a gas are directly related. If you increase the temperature of a gas in a closed container the bigger the gas becomes and the pressure in the can increases. V1= V2 T1 T2

2 12. State Guy-Lussac’s gas law. Temperature and pressure are directly related. That means as the temperature of a gas increases so does the pressure. Increase the temperature and increase the pressure. P1 / T1 = P2 / T2

13. What do we mean by an ideal gas? What is the combined gas equation? IDEAL GAS- A gas that behaves precisely according to the kinetic molecular theory. KMT STATES- 1. Are small particles far apart. 2. No attraction between them. 3. Move in random / straight line. 4. Molecules collide and exert force 5. Temperature determines kinetic energy COMBINED GAS EQUATION- (P1V1 / T1 = P2V2 / T2) The volume of gas varies directly width the number of gas molecules and the absolute temperature and inversely with the pressure.

14. Dalton’s law explains partial pressures of mixtures of gases. What does it say? Mixtures of gases behave independently of each other – the sum of all individual gas pressures in a mixture equals the total pressure. Ptotal = P1 + P2 + P3 etc

15. Weather balloons expand as they rise higher into the atmosphere. What does this tell you? It tells me that volume and pressure are inversely related. If one goes up other will go down. So, when balloon goes up pressure decreases and volume of the gas increases. So, as they go higher they expand. It also tells me that as you go higher into the atmosphere there is less pressure.

16. Explain the laws that govern diffusion in the alveoli as outlined by Graham, Fick and Henry. Graham’s Law outlines the rate of gas diffusion. It varies with the weight of the gas. Henry’s Law involves the amount of gas that can dissolve in a liquid. It varies with its solubility coefficient and the partial pressure. Fick’s Law describes gas diffusion through a membrane. It varies with the thickness of the membrane, the size of the surface area and the partial pressure gradient on each side of the membrane.

17. Describe the fluidic Flow laws under the principles of Bernoulli and Venturi. Fluidic flow through a pipe was first described by Bernoulli. He saw that the pressure in a tube decreased as the fluid flowed through the tube. The farther along it flowed, the lower the pressure was seen. He also observed that in a restriction in the size of the tube meant an increase in speed of the fluid through the restriction but also a greater drop in lateral pressure.

3 Venturi showed that the pressure could be fully restored with an entrainment port of outside air. It caused a negative pressure (sucking of air or liquid) that could be useful. He found that a fifteen degree angle was the optimal angle to use.

18. How is flow related to resistance in a circuit? It is common sense that if you increase the resistance of a flow through a tube the flow will slow down or it will take more work to maintain the same flow. A person with an increased resistance in the airway will have to work harder to breathe. He has to overcome the increased resistance. To keep resistance at the minimum use a short wide tube without any bends. The biggest factor is the diameter of the tube. If the tube narrows by one half – the resistance will increase by sixteen (the fourth power). See Poiseuille’s Law

19. Describe flow under laminar and turbulent conditions. What is Reynald’s number? Laminar flow through a tube is in a straight line pattern of concentric circles. There is an inner circle that is the fastest and the outer ring slowed by resistance of the wall of the tube. It is the ideal flow pattern as it causes the least resistance. Turbulent flow is chaotic without pattern. It has different characteristics then laminar flow. Reynald’s number is a combination of factors that change laminar flow to turbulent flow. It is written without units as 2,000.

20. Describe the Ohm’s Law that explains the flow of electricity. Ohm’s law describes the relationship between resistance, amperes and voltage. It states that with a higher flow (current) the higher the resistance. There is a direct analogy from electricity flow to gas flow fluidics. Ohm’s Law is… OHMS (resistance) = VOLTAGE / AMPERES

21. What role does surface tension play in alveolar gas exchange? Whose law explains it mathematically? Laplace law describes the stability of circular liquid spheres (bubbles). Small alveoli in the lungs are spherical structures coated with water, so they act much like bubbles. LaPlace’s law describes the behavior of surface tension and bubbles o Pressure P = 4 x ST /r o the units – dynes/centimeter Also, small bubbles are harder to inflate because of increased surface tension in smaller bubbles. Also gas exchange is not as good as the more surface area the better the gas exchange. (Fick’s Law)

4 VOCABULARY / KEY TERMS 1. Absolute Humidity The actual amount of water found in a given volume of gas, shown in g/m3 (meters cubed) or mg/L 2. Absolute Zero The temperature at which molecules cease moving (0 K, -273 C) 3. Adhesive forces Attractive forces between 2 different kinds of molecules 4. ATPD Atmospheric Temperature Pressure and Dry (No moisture) 5. ATPS Atmospheric Temperature Pressure and Saturated (100% RH) 6. Avogadro’s Law At conditions of constant temperature and pressure, the volume of a sample of ideal gas is directly proportional to the number of moles of gas present. 7. Barometer An instrument that measures the pressure of the atmosphere (i.e. air pressure) 8. Bernoulli Principle As the forward velocity of a gas increases, its lateral pressure decreases and its forward pressure increases. 9. Boyle’s Law Volume and pressure are inversely related; as pressure increases volume decreases. Formula V1P1 = V2P2 10. BTPS Body Temperature Pressure Saturated (37C, atmospheric pressure, and 47mmHg) 11. Charles Law Volume and temperature are directly related. If you increase the temperature of a gas you will increase the pressure it exerts. (Temperature must be in Kelvin) 12. Cohesive forces Cohesive forces are attractive forces between like kinds of molecules. These forces generate surface tension. Example water and oil. 13. Compliance Is related to elasticity. It is the amount of volume change for each unit of pressure change. 14. Condensation Is basically the opposite of evaporation. It is the conversion of a substance in its gaseous state to its liquid state. 15. Conduction The transfer of heat from a hot area to a cold area. It involves direct touching – contact. 16. Convection The indirect transfer of heat from one area to another. Does not involve touching like conduction. 17. Critical pressure The pressure exerted by a vapor at its critical temperature.

5 18. Critical temperature The highest temperature at which a substance can exist as a liquid, regardless of the pressure exerted upon it. (Water can exist as a vapor or a liquid at certain temperatures depending on the pressure that is exerted on it) 19. Density How thick or solid something is. Its mass divided by its volume. Formula D = M/V 20. Elastance Able to spring back to its original shape, size after being stretched, squeezed etc. flexible. 21. Evaporation Changing a liquid to a gas by using heat. 22. Fick’s Law Diffusion of a gas through a membrane. Like gas exchange in the lungs. It is related to the area available for the gas to enter, the partial pressure on each side of the membrane and how thick the membrane is that the gas has to pass through. 23. Graham’s Law The rate of diffusion of a gas is related to the solubility co-efficient of the gas and inversely related to the square root of the molecular weight of the gas. 24. Heisenberg’s Uncertainty The act of observing something changes the nature of the thing being observed. A student therapist will give a treatment procedure differently with an instructor watching then alone. 25. Henry’s Law Describes the amount of dissolved gas in a liquid depends on: 1. the partial pressure 2. Solubility co-efficient 26. Hook’s Law Describes stretching. Elastance and compliance compare change in pressure to change in volume. Formula… 27. Hygrometer An instrument that floats in a liquid to measure its specific gravity. It compares the liquid’s density to water. If it is greater then 1, is denser than water, less than 1 is less dense than water. 28. Kinetic energy Energy that an object possesses when it is in motion. 29. Laminar flow The movement of fluids through tubes with smooth surfaces and fixed radii. (The pressure required to produce a given flow is directly related to the viscosity, the length and radius of the tube.) 30. Laplace’s Law Pressure within a sphere is directly related to the surface tension of the liquid and inversely related to the radius of the sphere. Formula P = 2(ST/r) 31. Latent heat of vaporization The amount of heat that must be added to a substance to cause a complete change of state (from a liquid to a gas vapor).

6 32. mmHg mmHg- A unit of measurement for pressure on a barometer. You read the height of mercury columns in millimeters. 33. Occam’s Razor When given a choice of solutions, pick the simplest one. Do not complicate matters. A variation of K.I.S.S. principle – Keep It Simple Stupid 34. Ohm’s Law The relationship among voltage, current and resistance. The higher flow (current) the higher the resistance Resistance=Voltage/amperes or V=*P/R 35. Poiseuille’s Law A diameter of a tube through which a liquid flows affects the rate of fluid movement. Flow rate is directly related to the pressure gradient and inversely related to the diameter of the tube (airway) carrying the gas. The greater the flow rate the greater the pressure difference. 36. Potential energy The energy a body possesses by virtue of its position. Formula PE = MxH 37. Reynald’s number The mathematical number (2000) that signifies the change from laminar flow to turbulent flow. It includes… 38. Relative humidity The ratio of actual to potential water vapor in a volume of gas (ex a percentage of how much is present as compared to how much it could hold.) 50% humidity holds half as much as it could hold. 39. Standard atmosphere A standard atmosphere equals 760 mmHg, 14.7 psi, 1034 cmH20 or 101.3 Kpa It is the pressure exerted by the gases in the atmosphere around us. We live in a fluidic environment and it exerts a pressure on us. Equivalent pressures for one standard atmosphere:  760mmHg  1034cmH2O  1407psi  33 feet of sea water (34 feet of fresh water) 40. STPD This is a baseline measurement used to compare apples to apples. It is an acronym for Standard Temperature Pressure Dry. That is 0 degrees Celsius, 1 atmosphere and no water vapor pressure. 0 degrees Celsius, 760mmhg, no humidity 41. Surface tension Surface tension is caused by the cohesion forces of a liquid. Surface tension is the force on the surface (skin) of a liquid that is a barrier for molecules to leave the liquid into the air. It can be measured using LaPlace’s law. It is a factor in keeping alveoli inflated. Too much surface tension could cause an alveolus to collapse and not exchange gas normally. 42. Torr

7 The same as 1 mmHg. Named after Torricelli who first described and measured atmospheric pressures 43. Triple Point The temperature-pressure point at which a substance can exist with all three states of matter at equilibrium. 44. Turbulent flow A chaotic flow pattern usually found in the larger airways. 45. Venturi tube An entrainment port using Bernoulli’s principle. 46. Viscosity The term used to describe how thick and resistant to flow a fluid is. A sputum with a high viscosity is very hard to suction.

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