physical principles ret 2274 respiratory therapy theory i module 1.0

Physical Principles

RET 2274

Respiratory Therapy Theory I

Module 1.0

Atom, Molecules, Compounds are the building blocks of all matter

Molecules and States of Matter

Three Primary States of Matter


GasSolid Liquid


SolidA solid is a condensed structure in which strong intermolecular bonds determine a definite shape and volume.


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.


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


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


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


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)


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)


Density (p) A mass per unity volume, or m/V.

Weight p (density) x V (volume) x g (acceleration of gravity)


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.


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.


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


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


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


Viscosity The resistance to movement between

adjacent fluid molecules


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


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


Work of Breathing The work necessary to move air (or other

gases) through breathing cycles (inspiration/expiration)


Work of Breathing Mechanical ventilators do the work of

breathing for patients who cannot do it on their own


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.


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)


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


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)


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.


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


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.


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.


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


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.


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

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

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.

Thermodynamics and Heat Exchange

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

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

• Boyle’s Law states that pressure is inversely proportional to volume.

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 Laws

• Charle’s Law predicts the effect of temperature on a fixed amount of dry gas.

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.


• 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


• Dalton’s Law of Partial Pressure

Properties of Gases

Composition of Earth’s Atmosphere


• 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.


• 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


• 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


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


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)


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

Condensation


• 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.


• 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


• 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


• 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


• 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.


Figure 50-7: Principle of continuity. Note that fluid velocity is related inversely to the cross-sectional area.


• 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


• 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.


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


• 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


• 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


• Turbulent Flow is a jumbled mixture of velocities across the section of tube – friction is increased during turbulent flow


Figure 50-8: (A) Laminar flow. (B) Turbulent flow.


• Transitional Flow is mixture of laminar and turbulent flow patterns Flow in the respiratory tract is mainly transitional


• Reynolds Number describes factors associated with the generation of laminar or turbulent flow, e.g., velocity, radius, density, viscosity

• Reynolds Numbero >3000 = Turbulento 2000 – 3000 = Transitionalo <2000 = Laminar

physical principles ret 2274 respiratory therapy theory i module 1.0

Documents

states of matter slide

work mass

mass weight

work stress

molecular mass

x g slide

shear stress pressure

area force