physical principles ret 2274 respiratory therapy theory i module 1.0
TRANSCRIPT
Molecules and States of Matter
SolidA solid is a condensed structure in which strong intermolecular bonds determine a definite shape and volume.
Molecules and States of Matter
Liquid Composed of molecules
that can move about freely, has a definite volume without definite shape. Liquids are denser than gases. Like solids, liquids are difficult to compress.
Molecules and States of Matter
Gas The intermolecular bonds of
a gas are weak. A gas is compressible and completely fills an enclosed space. Both gases and liquids are considered fluids, that is, substances that can flow.
All three states of matter have a characteristic elasticity, or reversible deformability
Molecules and States of Matter
GasSolid Liquid
Systeme' International d’Unites (SI system) An international system of measurement that
is universally accepted but not always used SI unit for measuring pressure
Pascal (Pa; 1 newton/m2)
Common units for pressure used in the clinical setting cm H2O for gases mm Hg for liquids
Units of Measurement
Units of Measurement
Pressure can also be measured indirectly as the height of column of liquid:
Centimeters of water pressure (cm H2O)
Millimeters of mercury (mm Hg)
Both mercury and water columns are still used in clinical practice, especially when vascular pressures are being measured
Units of Measurement
Familiarity with the symbols used in respiratory physiology is essential to understand common terminology
Mass, Force, Stress, Pressure, and Work
Mass The amount of substance determined by the
number and type of molecules
The molecular mass of a substance is the number of moles (mol) of a substance, and 1 mole is Avogadro’s number (6.023 X 1023)
Mass, Force, Stress, Pressure, and Work
Force A mechanical energy applied to a body.
Force = (mass x acceleration)
Weight describes the force due to the acceleration of gravity (9.8 m/s2) acting upon a mass
Weight = (m x g)
Mass, Force, Stress, Pressure, and Work
Density (p) A mass per unity volume, or m/V.
Weight p (density) x V (volume) x g (acceleration of gravity)
Mass, Force, Stress, Pressure, and Work
If an object has a mass of 1 kg on the earth, it would have a mass of ______ on the moon. However, it would weigh one-sixth as much.
Mass, Force, Stress, Pressure, and Work
If an object has a mass of 1 kg on the earth, it would have a mass of 1 kg on the moon. However, it would weigh one-sixth as much.
Mass, Force, Stress, Pressure, and Work
Stress The force applied to an area
Force applied at an angle generates shear stress
Pressure Is force per unit area e.g., 1lb/in2
When measuring pressure within an oxygen cylinder, pounds per square inch (psi) is used
Mass, Force, Stress, Pressure, and Work
Strain The physical deformation or change is shape
of a structure or substance – usually caused by stress
Elasticity The amount of reversible deformability that
can be generated by a stress yet allow the structure or substance to return to its original shape
Mass, Force, Stress, Pressure, and Work
Elasticity
Gas is highly elastic, its volume can be compressed relatively easily
Fluids, such as liquids, are less elastic and behave as if incompressible
Solids lack elasticity compared with gases or liquids
Mass, Force, Stress, Pressure, and Work
Viscosity The resistance to movement between
adjacent fluid molecules
Mass, Force, Stress, Pressure, and Work
Viscosity Example: When there is an increase in red
blood cells (polycythemia), the heart must work harder to circulate the blood because it is more viscous
Mass, Force, Stress, Pressure, and Work
Work A force causing displacement of matter does
work
For gases, a force can be measured as pressure, and the displacement is the volume change to the lungs
Using SI units, work is expressed in (N.m) or joules (J) or joules per liter
Mass, Force, Stress, Pressure, and Work
Work of Breathing The work necessary to move air (or other
gases) through breathing cycles (inspiration/expiration)
Mass, Force, Stress, Pressure, and Work
Work of Breathing Mechanical ventilators do the work of
breathing for patients who cannot do it on their own
Mass, Force, Stress, Pressure, and Work
Pascal’s Law Liquid pressure depends only on the height
(h) of the vessel and not on the vessel’s shape or the total volume of liquid.
Mass, Force, Stress, Pressure, and Work
Hydrostatic Pressure The weight of a fluid generates
static fluid pressure due to the force of gravity, which varies according to the density and depth within the fluid container.
Atmospheric (barometric) pressure is an example of static fluid pressure – as elevation increases, atmospheric pressure decreases (shorter column of atmospheric gas)
Mass, Force, Stress, Pressure, and Work
Compliance The volume change to sphere-like structures such as
lungs or alveoli caused by a pressure change is the compliance, or stiffness, of the sphere.
Compliance = Volume
Pressure
Respiratory System Compliance Is a composite of two compliances, lung compliance
and chest wall compliance
Mass, Force, Stress, Pressure, and Work
Elastance The quality of recoiling or returning to an original form
after the removal of pressure. The reciprocal of compliance (Mosby's Medical Dictionary, 8th edition. © 2009, Elsevier.)
Elastance = Pressure
Volume A measure of the tendency of a hollow organ to recoil
toward its original dimensions upon removal of a distending or compressing force. It is the reciprocal of compliance. (The American Heritage® Medical Dictionary Copyright © 2007, 2004 by Houghton Mifflin Company)
Mass, Force, Stress, Pressure, and Work
Surface Tension Surface tension is the
property of a liquid that tends to reduce the surface of a liquid toward a minimum, pulling the surface molecules inward. This is what causes water to bead up rather than spread out.
Mass, Force, Stress, Pressure, and Work
Surface Tension Laplace’s Law: In a liquid sphere, the pressure
required to distend the sphere is directly proportional to the surface tension of the liquid and inversely proportional to the sphere’s radius
Mass, Force, Stress, Pressure, and Work
Surface TensionRelationship described by Laplace’s law. Bubble A (left), which has the smaller radius, has the greater inward or deflating pressure and is more prone to collapse than is bubble B (right). Because the two bubbles are connected, bubble A would tend to deflate and empty into bubble B. Conversely, because of bubble A’s greater surface tension, it would be harder to inflate than bubble B.
Mass, Force, Stress, Pressure, and Work
Surfactant A fluid that reduces surface tension
Surfactant is produced in the lungs (it can also be manufactured synthetically). It reduces the surface tension of fluid in the lungs. This keeps them from collapsing when an individual exhales and makes them easier to inflate when inhaling.
Mass, Force, Stress, Pressure, and Work
Surfactant Surfactant also reduces the pressure
differences between alveoli of different diameters
Without surfactant, smaller alveoli would empty into larger ones because of the greater surface tension in the smaller alveoli
Mass, Force, Stress, Pressure, and Work
Surface Tension The lungs resemble clumps of
bubbles. It follows therefore that surface tension plays a key role in the mechanics of ventilation
Abnormalities in alveolar surface tension occur in certain clinic conditions, e.g., Babies that are born very prematurely often lack adequate surfactant and must receive surfactant replacement therapy immediately after birth in order to breathe.
Mass, Force, Stress, Pressure, and Work
Surface Tension Abnormalities in alveolar
surface tension occur in certain clinic conditions.
Babies that are born very prematurely often lack adequate surfactant and must receive surfactant replacement therapy immediately after birth in order to breathe.
Temperature
Temperature describes the amount of heat, or thermal energy, present in a system
Three temperature scales are common:
o Fahrenheit (° F)o Celsius (° C)o Kelvin (absolute) (K)
Temperature
Fahrenheit Used in Healthcare Divides the temperature range between
freezing and boiling into 180 gradations, or degrees
Freezing point of water = 32º F
Boiling point of water = 212º F
Temperature
Celsius (C) Used in Healthcare Divides the temperature range between
freezing and boiling into 100 gradations, or degrees
Freezing point of water = 0º C
Boiling point of water = 100º C
Temperature
Kelvin (K) Zero degrees K = absolute zero
Absolute zero is the concept that a temperature exists at which there is no kinetic energy (energy of motion) – exists in theory only
Freezing point of water = 273 K
Boling point of water = 373 K
Note: To covert degrees Celsius to degrees Kelvin, simply add 273
Example: 25º C = 25 + 273 = 298º K
Temperature
Linear relationship between gas molecular activity, or pressure, and temperature. The graph shows comparable readings on three scales for five temperature points
Freezing point of water
Boiling point of water
Thermodynamics and Heat Exchange
Thermodynamics describes changes in the thermal state of a system by adding or removing energy, such as when changes in pressure, volume, or temperature alter the state of the substance.
When a change of state requires the addition of energy, the process is called endothermic.
An exothermic process gives off energy.
Gas Laws
The Ideal Gas Law defines a relationship between pressure, volume, temperature, and the number of molecules of a gas.
Pressure and volume are inversely related, whereas temperature is directly proportional to volume or pressure
Gas Laws
(A) A mass of gas in the resting state exerts a given pressure at a given temperature in a cylinder
(B) As the piston compresses the gas, the molecules are crowded closer together, and the increased energy of molecular collisions increases both the temperature and the pressure
(C) Conversely, as the gas expands, molecular interaction diminishes and the temperature and pressure fall
Gas Laws
• Gay-Lussac’s Law The pressure of a gas of fixed mass and fixed volume is directly proportional to the gas' absolute temperature.
• The pressure in an oxygen tank will change directly with changes in temperature.
• P1/T1 = P2/T2
Gas Laws
Two escape trailer before explosion
The Associated Press
Tuesday, September 4, 2012
HENDERSONVILLE — Henderson County fire officials say a Bat Cave woman and her friend narrowly escaped serious injury when they left a burning trailer before it exploded.
The Times-News of Hendersonville reports that a family member said Elizabeth Lawter awoke to find her bed on fire after a discarded cigarette caught a nearby trashcan on fire and spread to the bedding.
Fire Marshal Wally Hollis said several oxygen tanks in the trailer exploded shortly after the two occupants left Sunday morning. Hollis said one large tank was exposed to the flames, leading to the explosion. Her mother said Lawter suffers from diabetes and chronic emphysema.
The blast threw the trailer's roof to the edge of U.S. Highway 64 and also blew out the windows of an adjacent trailer.
Told ya!
Gas Laws
• Boyle’s Law states that pressure is inversely proportional to volume.
• If a volume of gas is halved, pressure will double, given a constant mass and temperature
Gas Laws
Let’s try and understand Boyle’s law using a simple example. At the surface we are subjected to 1 ATM (atmosphere) of pressure. At 33ft underwater, we are subjected to 2 ATM; i.e. 1 ATM of Air pressure and 1 ATM of water pressure.
So if we take a 1 liter Coke bottle filled with air faced down with no cap on, to 33ft (10m) underwater, we would see that the volume of air decreases to around ½ a liter of air, and water would begin filling into the bottle without any of the air escaping. Because at 33ft the pressure has increased of 2 ATM or has doubled, thereby halving the volume of the air. If we take the bottle down to 66ft (20m), we would be at 3 atmospheres of pressure and the air in the bottle would be 1/3 of a liter and so on.
Now assume we add air into the coke bottle from our scuba tanks at the depth of 33ft (10m) topping off the half full bottle, cap the bottle tightly, then begin to ascend.(remember the air in our scuba tank is also being subjected to Boyle’s law ) As we rise, the pressure decreases, causing the already compressed air to expand. At the surface the volume of the air in the 1 liter bottle would have doubled to 2 liters probably causing the bottle to burst on the way up.
Gas Laws
• Charle’s Law states that at constant pressure, the volume of a given mass of an ideal gas increases or decreases by the same factor as its temperature on the absolute temperature scale (i.e. the gas expands as the temperature increases).
Gas Mixtures and Partial Pressures
• Dalton’s Law of Partial Pressure describes the behavior of physical mixtures of gases and vapors.
• The partial pressure of each particular gas is equal to the fractional concentration times the total atmospheric pressure.
Gas Mixtures and Partial Pressures
• Dalton’s Law of Partial Pressure
• Many gases exist together as mixtures, for example air, which contains mostly oxygen and nitrogen
• The pressure exerted by a single gas is called its partial pressure
• The total pressure of a mixture of gases must equal the sum of the partial pressures of all component gases
PressureTotal = Pressure1 + Pressure2 ... Pressuren
Gas Mixtures and Partial Pressures
• Physical combinations of gases mix uniformly and are evenly distributed in any particular confined space.
• The same fractions of oxygen and nitrogen are present in Death Valley (86 m below sea level) as on Mount Everest (elevation 8850 m), although their partial pressures vary greatly according to their respective altitude.
Humidity, Water Vapor, Evaporation
• Most gases encountered in physiologic conditions are combination of various dry gases, but they also contain water vapor (gas), which combines with the other gases according to Dalton’s law of partial pressures.
• Water is particularly important as a vapor under conditions encountered in respiratory care.
Humidity, Water Vapor, Evaporation
• Evaporation and Condensation• A water surface emits molecules of vapor
continuously by evaporation
• As vapor molecules hit the surface of a liquid, some are absorbed into the liquid by condensation
Humidity, Water Vapor, Evaporation
• Between 100°C and 0°C there is saturation pressure (or partial pressure of water) at any given temperature at which water will condense
• Temperature defines a limit to the maximum amount of water vapor that can be contained in air at that temperature
Humidity Therapy and Humidifiers
Absolute Humidity Is the actual content or weight of water present
in a given volume of gas Expressed as:
Milligrams per liter (mg/L)
Also know as water content
Humidity Therapy and Humidifiers
Relative Humidity (RH) Is the ratio of actual content or weight or the
water present in a gas relative to the sample’s capacity to hold water at that temperature Expressed as a percentage
%RH = absolute humidity X 100
humidity capacity
When the amount of water that a gas contains at a given temperature is equal to the gas’s capacity, the RH is 100% - described as saturated
Humidity Therapy and Humidifiers
Relative Humidity (RH) If absolute humidity is held
constant, increasing the temperature of the gas will decrease the RH(Temp RH)
If absolute humidity is held constant, decreasing the temperature of the gas will increase the RH or it will remain at 100%(Temp RH)
Humidity Therapy and Humidifiers
Condensation Cooling a gas that has an RH of 100%
decreases its capacity to hold water, which results in water being squeezed out of the gas
Temp RH
Humidity, Water Vapor, Evaporation
• At 1 atm, fully humidified or saturated air at body temperature has a PH2O of 47 mm Hg. Other gases account for the remainder of the 760 mm Hg, or 713 mm Hg.
Humidity, Water Vapor, Evaporation
• Percentage of Body Humidity (%BH)
• %BH is the ratio of actual water vapor content to the water vapor capacity in a saturated gas at 37°C.
%BH = Content x 100%
Capacity (43.8 mg/L)
• The water content (absolute humidity) of fully saturated gas at body temperature is 43.8 mg/L
Humidity, Water Vapor, Evaporation
• A humidity deficit occurs whenever inspired gas is not fully saturated at body temperature, requiring the body to add water to inspired gases to achieve full saturation.
Humidity deficit = water vapor content – 43.8 mg/L
• The difference is the burden on the airway to humidify the inspired gas
Properties of Gases
Henry’s Law states that at a constant temperature, a gas dissolves in solution in proportion to its partial pressure
William Henry (chemist)
Properties of Gases
Henry’s Law also states that the capacity of a liquid to carry a gas decreases as a temperature increases
High temperatures decrease solubility
Low temperatures increase solubility
Leave a carbonated drink open and out of the refrigerator and it will quickly go flat
Properties of Gases
Diffusion is the process whereby molecules move from areas of high concentration to areas of lower concentration
Graham’s law states that the rate of diffusion of a gas (D) is inversely proportional to the square root of its density:
Lighter gases diffuse rapidly, whereas heavy gas molecules diffuse more slowly
In a liquid medium, both Graham’s law and Henry’s law affect the rate of diffusion of gases.
Gases in Solution, Diffusion, Osmosis
• Osmosis is the movement of a solvent by diffusion, primarily, through a semipermeable membrane that does not permit movement of larger solute molecules.
• A solvent diffuses across the membrane from an area of lesser to greater concentration
Gases in Solution, Diffusion, Osmosis
• Fick’s law relates the factors that affect the transmembrane transfer of solute during osmosis
• The total diffusion rate of a gas across a barrier (such as the alveolar membrane in the lung) is directly proportional to the:• Cross-sectional area available for diffusion (Lung size)• Difference in concentration gradients of the diffusing
gases• Thickness of the barrier (e.g., alveolocapillary
membrane)
Conversion of Gas Volumes
• Several sets of conditions are commonly encountered in respiratory therapy because of the conditions under which certain stored (dry) or measured gases (body temperature, humidified).
Flow of Gases and Other Fluids
• Flow is the movement of a specified volume of fluid (gas or liquid) in a particular period of time (Volume/Time)• e.g., liters of air / minute
• The flow of gas through tubes is a key physical phenomenon in respiratory physiology:
• Flow of air into and from the lungs
• Flow of gas through a ventilator circuit
Flow of Gases and Other Fluids
• Principle of Continuity is the concept that states that if any liquid flows through a rigid pipe, the mass of fluid entering a tube must equal the mass leaving the tube
• Flow Velocity is the distance a fluid moves over a time period (Distance/Time)• e.g., Velocity = centimeters/second
Flow of Gases and Other Fluids
• The product of velocity and the area of the tube through which a fluid moves defines the volume of fluid moving over time.
• If the diameter (hence area) of a section of the tube increases, the velocity decreases through that segment because the same mass entering must equal the mass exiting the tube (principle of continuity).
• Diameter and velocity are therefore inversely related.
Flow of Gases and Other Fluids
Figure 50-7: Principle of continuity. Note that fluid velocity is related inversely to the cross-sectional area.
Flow of Gases and Other Fluids
• The Bernoulli principle describes the pressure in a fluid as the velocity changes. According to the Bernoulli theorem, a flowing fluid’s lateral pressure must vary inversely with its velocity
Flow of Gases and Other Fluids
• The Venturi principle is an application of the Bernoulli principle and the law of continuity that explains the entrainment of fluids through an open port in a tube.
• When a flowing fluid encounters a very narrow passage, its velocity can increase greatly and cause the fluid’s lateral pressure to fall below that exerted by the atmosphere and pull another fluid into the primary flow stream.
Flow of Gases and Other Fluids
The Venturi principle The amount of air
entrained depends on both the diameter of the jet orifice and the size of the air entrainment ports
Flow of Gases and Other Fluids
• Viscosity is described as the internal friction of a fluid and is independent of the density of the fluid (gas or liquid).
• For gas movement, viscosity increases with temperature because the frequency of collisions between molecules is greater at higher temperatures
• Viscosity in liquids is increased at lower temperatures
Flow of Gases and Other Fluids
• Laminar Flow is the orderly flow of a fluid through a straight tube as a series of concentric cylinders slide over one another – friction is decreased during laminar flow
Flow of Gases and Other Fluids
• Turbulent Flow is a jumbled mixture of velocities across the section of tube – friction is increased during turbulent flow
Flow of Gases and Other Fluids
• Transitional Flow is mixture of laminar and turbulent flow patterns Flow in the respiratory tract is mainly transitional