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Respiratory Therapy Physics Week 1

Respiratory Therapy Physics Week 1. First-year students at Med School were receiving their first Anatomy class with a real dead human body. They all gathered around the surgery table with the body covered with a white sheet.

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Respiratory Therapy Physics Week 1

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  1. Respiratory TherapyPhysicsWeek 1

  2. First-year students at Med School were receiving their first Anatomy class with a real dead human body. They all gathered around the surgery table with the body covered with a white sheet. The professor started the class by telling them: "In medicine, it is necessary to have 2 important qualities as a doctor. The first is that you not be disgusted by anything involving the human body." For an example, the professor pulled back the sheet, stuck his finger in the EYE of the corpse, withdrew it and stuck his finger in his mouth." “Go ahead and do the same thing," he told his students. The students freaked out, hesitated for several minutes, but eventually took turns sticking a finger in the EYE of the dead body and sucking on it. When everyone had finished, the Professor looked at them and told them, "The second most important quality is observation. I stuck in my Middle finger and sucked on my index finger. Now learn to pay attention to your patients, their life may depend upon it."

  3. Objectives • Overview of the course • Introduction to RT physics • Absolute temperature and pressure • Temperature scales and conversions • Conditions of measurement STPD, BTPS and ATPS

  4. Reading and HW • Each week you must come to class prepared. • Review the syllabus for important dates and course topics • Please read the textbook and notes completely and be prepared to discuss it’s contents in class

  5. States of Matter Physics is the branch of science that deals with the interactions of matter and energy.

  6. According to the law of conservation of energy, energy cannot be created or destroyed: energy can only be transferred. All matter is comprised of molecules that are in constant motion. The degree of this motion differs among three states of matter (solid, liquid and gas) and their intermolecular forces

  7. Kinetic Theory • States that the atoms & molecules that make up matter are in constant motion. • Temperature influences movement of molecules. Hot objects move more than cold objects. Increasing kinetic energy increases temperature • Thermal energy = molecular Kinetic Energy + Potential Energy

  8. The 3 states of matter http://www.youtube.com/watch?v=guoU_cuR8EE

  9. States of Matter • Solids – have a high degree of internal order; their atoms have a strong mutual attractive force • Liquids – atoms exhibit less degree of mutual attraction compared with solids, they take the shape of their container, are difficult to compress, exhibit the phenomenon of flow • Gases – weak molecular attractive forces; gas molecules exhibit rapid, random motion with frequent collisions, gases are easily compressible, expand to fill their container, exhibit the phenomenon of flow

  10. States of Matter All matter possesses energy. There are 2 types of internal energy: The energy of position, and the energy of motion. • Internal energy of matter • Potential energy (Position) The strong attractive forces between molecules that cause rigidity in solids • Kinetic energy (Motion) Gases have weak attractive forces that allow the molecules to move about more freely, interacting with other objects that they come in contact with • Internal energy and temperature • The two are closely related: internal energy can be increased by heating or by performing work on it. • Absolute zero = no kinetic energy

  11. Potential energy is stored energy. • Kinetic energy is the energy that an object possesses when it is in motion. http://www.youtube.com/watch?v=vl4g7T5gw1M

  12. Change of State • Liquid-solid phase changes (melting and freezing) • Melting = changeover from the solid to the liquid state • Melting point = the temperature at which melting occur. • Freezing = the opposite of melting • Freezing point = the temperature at which the substance freezes; same as its melting point

  13. Temperature • Temperature: the amount of heat energy in matter expressed in terms of a specific scale • Three common scales of temperature: • Celsius (used in health care) • Body temperature 37 degrees C (+/-1) • Boiling point of water 100 degrees C • Freezing point of water 0 degrees C • Absolute 0 (no molecular movement) -273 C • Fahrenheit (common US household scale) • Body temperature 98.6 degrees (+/- 1) • Boiling point of water 212 degrees F • Freezing point of water 32 degrees F • Absolute 0 (no molecular movement) -280 F • Kelvin (used in research) • Absolute 0 (no molecular movement) 0 Kelvin

  14. Temperature • Absolute Temperature Scale: A temperature measurement scale in which the 0 point is absolute 0 or the temperature at which all molecular motion ceases. Absolute 0 temperature is about -273 Celsius. The absolute temperature scale for Celsius is called the Kelvin temperature scale. Celsius temperatures can be converted to Kelvin temperatures by adding 273 degrees to the Celsius temperature as shown below: • Kelvins = Celsius + 273 Example: Convert 37 C to Kelvins • Kelvins = 37 + 273 = 310 Kelvins To convert Kelvin temperatures to Celsius, subtract 273 as shown below: • Celsius = Kelvins - 273 • Example: Convert 298 Kelvins to Celsius • Celsius = 298 K - 273 = 25 Celsius

  15. Temperature • "Gauge" Temperature Scale: A temperature measurement scale in which the 0 point is something other than absolute 0. • For example, in the Celsius temperature scale, the 0 point is the freezing point of water and in the Fahrenheit temperature scale the 0 point is 32 degrees below the freezing point of water. • In the hospital, the Celsius scale is used to report patient temperatures. This is somewhat confusing for patients who are used to ambient temperatures that are usually reported in Fahrenheit temperatures. For this reason, it is important for you to be able to convert temperatures from one scale to the other.

  16. Temperature Conversion To convert Fahrenheit to Celsius, use the following formula: C= .55 x (F - 32) Example: Convert 60 Fahrenheit to Celsius C = .55 (60 - 32) = .55 x 28 = 15 Celsius To convert Celsius to Fahrenheit, use the following formula:   F= (1.8 x C) + 32 Example: Convert 20 Celsius to Fahrenheit F = (1.8 x 20) +32 = 36 + 32 = 68 Fahrenheit

  17. Pressure • Many techniques have been developed for the measurement of pressure and vacuum. Instruments used to measure pressure are called pressure gauges or vacuum gauges. • A manometer could also refer to a pressure measuring instrument, usually limited to measuring pressures near to atmospheric. The term manometer is often used to refer specifically to liquid column hydrostatic instruments.

  18. Pressure • Pressure: A measurement of force per unit area, ie: pounds per square inch (PSI) • Absolute Pressure Scale: A pressure scale in which the 0 point is a complete vacuum or the pressure at which all molecular motion ceases. Absolute pressure includes atmospheric pressure. • Gauge Pressure Scale: A pressure scale in which the 0 point is atmospheric pressure or the pressure of the atmosphere pushing down on a given point on the earth.

  19. Absolute Pressure Scale • Everyday pressure measurements, such as for tire pressure, are usually made relative to ambient air pressure. In other cases measurements are made relative to a vacuum or to some other specific reference. When distinguishing between these zero references, the following terms are used: • Absolute pressure is zero-referenced against a perfect vacuum, so it is equal to gauge pressure plus atmospheric pressure. • ATMOSPHERIC PRESSURE AT SEA LEVEL IS 760 torr (mmHg) • Positive pressure is above atmospheric pressure and negative pressure is below atmospheric pressure • Atmospheric pressure varies based on altitude • Gauge pressure is zero-referenced against ambient air pressure, so it is equal to absolute pressure minus atmospheric pressure. Negative signs are usually omitted. To distinguish a negative pressure, the value may be appended with the word "vacuum" or the gauge may be labeled a "vacuum gauge." • Differential pressure is the difference in pressure between two points.

  20. Pressure Conversions • Pressure measurement scales can be either gauge or absolute and a different conversion factor is needed for each scale: • PSIG is the pressure read from a gauge which reads the difference between the pressure in what's being measured (lungs, gas tank…) and the pressure of the atmosphere. PSIA is the total pressure including the pressure of the atmosphere.PSIG + 1 atmosphere = PSIAPSIA - 1 atmosphere = PSIG1 atmosphere is approximately 14.7 PSI • PSIA = PSIG + 14.7 (14.7 psia = 0 psig) • Ex: Convert 1 PSIG to PSIA. PSIA= 14.7 + 1 = 15.7 PSIA • cmH20 (absolute) = cmH2O (gauge) + 1034 • torr(absolute) = torr (gauge) + 760

  21. Pressure Conversions • cmH2O It is frequently used to measure central venous pressure, intracranial pressure while sampling cerebrospinal fluid, as well as determining pressures during mechanical ventilation (very common in Respiratory!) • It is defined as the pressure exerted by a column of water of 1 cm in height at 4 °C (temperature of maximum density) at the standard acceleration of gravity • cmH20 (absolute) = cmH2O (gauge) + 1034 • Ex: Convert 100 cmH2O gauge to cmH2O absolute = 100 + 1034 = 1134 cmH2O Absolute

  22. Pressure Conversions • torr (same as mmHg) • torr is used to measure blood pressure and atmospheric pressure. • 1 torr = 1 atm, measured by a Barometer • At sea level 1 atm = 760 torr (mmHg) • torr(absolute) = torr (gauge) + 760 • 1 torr (Torr) is equal to 1.36centimeters of water (cmH2O) • 1 centimeter of water (cmH2O) is equal to 0.74 torr • Ex: Convert 100 torr to cmH2O = 100 x 1.36 = 136 cmH2O

  23. Measuring Pressure • With cm H2O and torr it is sometimes difficult to determine whether the reading is gauge or absolute. You must know if a certain parameter such as blood pressure is generally reported in torr absolute or gauge. As a general rule, if the reading is obtained from a "gauge" or manometer, then it is a gauge pressure reading.

  24. Negative Pressure • "Negative Pressure:" negative or minus gauge pressure is frequently used in respiratory care to describe gauge pressure conditions that are lower or less than 0 or atmospheric pressure. (same thing as vacuum pressure) • Example: Chest tube drainage pressure is usually set at -15 cm H2O or 15 cm H2O below atmospheric pressure. Example: -15 cm H2O gauge = 1019 cm H2O absolute. • 1034 cmH2O - 15 cmH2O = 1019 cm H20 • 1019 cmH2O in torr = 1019 x 0.74 = 754 torr (mmHg) ( which is below atmospheric, this is what creates the vacuum) • Negative absolute pressure is not possible because 0 absolute pressure represents a complete vacuum or the complete absence of pressure.

  25. Critical Temperature and Pressure • Critical temperature: • The temperature reached in which gaseous molecules cannot be converted back to a liquid, no matter what pressure is exerted on them. • The highest temperature at which a substance can exist in a liquid state. • Critical pressure: • The critical pressure of a substance is the pressure required to liquefy a gas at its critical temperature.

  26. Critical Temperature • Gases can be converted to liquids by compressing the gas at a suitable temperature. • Gases become more difficult to liquefy as the temperature increases because the kinetic energies of the particles that make up the gas also increase. • One reason why Oxygen is cooled down to liquefy and store

  27. critical temperature • The critical temperature of a substance is the temperature at and above which vapor of the substance cannot be liquefied, no matter how much pressure is applied. • Every substance has a critical temperature.

  28. Tubes containing water at several temperatures. Note that at or above 374oC (the critical temperature for water), only water vapor exists in the tube.

  29. Critical Pressure • The critical pressure of a substance is the pressure required to liquefy a gas at its critical temperature. Some examples are shown below.

  30. Critical temperature & critical pressure examples • Water boils at 100 C and has a critical temperature of 374 C. • Oxygen has a boiling point of -183 C and a critical temperature of about -119 C Below -183 C, oxygen can exist as a liquid. Above – 183 C, liquid oxygen becomes a gas. Above 217 atm, and a temperature of 374 C gaseous water cannot be converted back to a liquid no matter how much pressure is added

  31. Bulk Oxygen System • Here, the liquid O2 is allowed to exceed its critical temp & convert to gas.

  32. Conditions of measurement • Specific temperature, pressure and humidity conditions that are used to measure gases so that we can compare measurements, usually of gases, made by different people at different times. Conditions of measurement are abbreviated with upper case letters, ie: STPD. In respiratory care we commonly use three different conditions of measurement: • STPD: 0 Celsius, 1 atmosphere (760 torr), dry -- used mainly in chemistry, used in respiratory care to measure metabolic and nutritional values. • BTPS: 37 Celsius, 1 atmosphere (760 torr), saturated -- the conditions in the body, used in respiratory care to measure lung volumes. • ATPS: room temperature, room pressure, saturated -- ambient or room conditions, the temperature and pressure vary with the conditions in the environment or room. Used in respiratory care to convert room conditions to body conditions. • There are conversion equations and charts that can be used to convert from one set of conditions to another, ie: ATPS to BTPS. You will not be required to convert these conditions in this course.

  33. STPD • Symbol indicating that a gas volume has been expressed as if it were at standard temperature (0 degrees C), standard pressure (760 mm Hg absolute), dry; under these conditions a mole of gas occupies 22.4 liters. • STP refers to the use of a gas under standard (S) conditions of temperature (T), and pressure (P). That is, 0 degrees C and 760 mm Hg. The "D" means "dry", that is, containing no water. • Such conditions are important because if any one of them changes, then the actual amount of the gas changes, as well. • So at STPD conditions, the designated amount of gas is accurate.

  34. BTPS – measures body values verse normals • "Body Temperature and Pressure Saturated". The conditions of a spirometer are different from the human body, so you have to compensate for that or else the volumes that you measure from your spirogram will be off. • abbreviation for body temperature, ambient pressure, saturated with water vapor conditions of a volume of gas. For humans normal respiratory tract temperature is measured at 37° C, ambient pressure, and the partial pressure of water vapor at 37° C at 47 mm Hg.

  35. ATPS – measured outside the body • Measured at ambient temperature, pressure, saturated with water vapor (e.g. expired gas, which has cooled down): ambient temperature and pressure, saturated.

  36. HOMEWORK • STUDY! Review all handouts and read pages 249-252 • Complete PRACTICE PROBLEMS on page 252-253 #126-145 • Be prepared for a possible quiz on all conversions discussed (temperature and pressure) CALCULATORS OK • Read pages 165-175, 205-219, 202, 245-248 for next week

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