Techniques and Procedures I RC 170

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Techniques and Procedures I RC 170. Basic Physics For Respiratory Therapist. Energy. Energy - the ability to do work Work = force X distance Kinetic energy - energy that an object possesses when it is in motion.

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## Techniques and Procedures I RC 170

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### Techniques and Procedures IRC 170

Basic Physics

For

Respiratory Therapist

Energy
• Energy- the ability to do work
• Work = force X distance
• Kinetic energy- energy that an object possesses when it is in motion.
• Potential energy or stored energy- the energy an object possesses because of its position. (energy of position, gravitaxl)
Matter – has mass and occupies space
• Atomic Theory: all matter is composed of tiny particles called atoms.
• Kinetic Theory: atoms and molecules that make up matter are in constant motion

Figure 1-1 States of Matter

States of Matter
• Solid
• Limited atomic motion due to Van der Walls forces (mutual attracx)
• Mostly Potential Energy, very little Kinetic
• Hard to compress
• Liquid
• Freedom of motion - Some KE & some PE
• Takes shape of container
• Exhibits flow
• Hard to compress
• Gas
• very weak attractive forces - mostly KE
• Lacks Motion restrictions
• Able to Flow, expand/compress
Temp and Pressure scales
• Temp conversions: Box 1-3, page 9
• Pressure conversions: Box 1-4, page 9

1 ATM = 760 mmHg = 14.7 psi = 1034 cmH2O

1mmHg = 1.36 cmH2O

1st Law of Thermodynamics
• Energy can be neither created nor destroyed, only xformed in nature
• Energy gains must = energy losses
• Equal energy requirements to freeze/melt
Change of State

Boiling point: temperature at which a liquid converts to a gaseous state

Figure 1-3 Temperature Scales

Freezing point: temperature at which change occurs from a liquid

to a solid

Critical Pressure/Temp
• Critical Temperature: T at which a gas can’t be converted back to a liquid state at any pressure (-118 °C [182 °F] for O2)
• Critical Pressure: P required to convert a gas back to a liquid state at it’s critical temperature (716 psi for O2)
• Gas: state of matter above it critical temperature
• Vapor: state of matter below its critical temperature
Change of State
• Evaporation: Change from Liquid to Gas Below its boiling point
• Rate of evaporation increases with
• ↑ temperature, ↑surface area
• ↓ PB
• Sublimation: Change from solid to gas by-passing the liquid state
• Condensation: conversion of a substance from a gas to a liquid.
Heat Xfer
• 1st law tells us that 2 objects of differing temps will xfer energy (Heat) until at equilibrium
• 4 modes of heat xfer
• Conduction (direct contact, solids)
• Convection (direct contact, fluids)
• Evaporation/Condensation
• energy is xferd due to change of state
• Evaporative cooling

Hg Barometer

Figure 1-4 A mercury barometer

Aneroid Barometer

Figure 1-5 An aneroid barometer

Pressure and Humidity
• Water Vapor Pressure: P exerted by vapor due to kinetic activity which is T dependent. (Table 1-4 page 16)
• @ 37°C = 47 mmHg of VP
• Absolute Humidity: actual content of water present in a sample of gas.
• Relative Humidity: actual content of water present in a sample of gas relative to its total carrying capacity. Expressed in a %.

(Page 103 Egan: Table 6-3)

%BH & Humidity Deficit
• %Body Humidity – ratio of water vapor : capacity at body Temp. (37C)
• Humidity Deficit
• The difference b/w capacity & content
• Absolute Humidity at Body Temp
• 43.8 mg/L

Properties of Liquids

• Pascal’s Principle
• A Liquids Pressure is exerted in all directions
• Pressure exerted depends on Depth (height) & Density
• Viscosity
• Opposing Force to a liquids flow
• Directly proportional to molecular cohesive forces
• Increased Temp decreases viscosity
• Weakens molecular bonds

Properties of Liquids

Figure 1-6 A practical example of buoyancy.

Archimedes’s Principle: when an object is submerged in a fluid, it will

be buoyed up by a force equal to the weight of the fluid that is

displaced by the object……if the weight density of the object being

submerged is less than the weight density of the water, the object

will float

Properties of Liquids

&

Cohesion

Water Meniscus

Mercury Meniscus

(Cohesion)

21

Properties of Liquids

Figure 1-8 The molecular basis for surface tension

Surface Tension: cohesive forces between liquid molecules at a gas-

liquid interface. Box 1-5 Adhesive and Cohesive forces.

Properties of Liquids

Laplace's Law: the pressure within a sphere

is directly related to the surface tension of

the liquid and inversely related to the radius

of the sphere

Surface Tension forces cause a liquid to

have the tendency to occupy the smallest

possible area, which is usually a sphere.

Figure 1-9 Laplace's law.

Properties of Liquids

Capillary Action

24

Gas Laws
• Boyle’s: The volume that a gas occupies when it is maintained at a constant temperature is inversely proportional to the absolute pressure exerted upon it.
• With a constant temperature
• If you double the Press, your volume halves
• As press increases, Volume decreases & vice versa
• P1V1=P2V2 P1V1=P2V2

T1 T2

Boyle’s Law

Figure 1-10 Boyle’s Law

Boyle’s Law
• Joule-Thompson Effect
• Expansion Cooling
• Purging a cylinder
• Due to breaking of van der waals bonds
• Compression Heating
• Diesel engine
Gas Laws
• Charles’s: When the pressure of a gas is held constant, the volume of a gas varies directly with its absolute temperature
• Under Constant pressure
• Increase in temperature will increase the volume

V1 =V2

T1 T2

Charles’s law

Figure 1-11 Charles's law

Gay-Lussac’s law
• Gay-Lussac’s: if the volume of a gas is held constant, the gas pressure rises as the absolute temperature of the gas increases.
• Volume is constant
• Pressure increases as temperature increases

P1=P2

T1 T2

Gay-Lussac’s law

Figure 1-12 Gay-Lussac’s law

Combined Gas Law

Combined Gas Law

36

Dalton’s law of Partial pressures
• The sum of the partial pressures of a gas mixture equals the total pressure of the system. PB= 760 mm Hg

PO2 = (760) (0.21) PO2= 159 mm Hg

PB= PO2+ PN2 + PCO2 + P (trace gases)

PB= (760)(0.21)+ (760)(0.78)+ (760)(.003)+ (760)(.07)

PB = 760 mm Hg

Laws of Diffusion
• Diffusion: net movement of gas molecules from a high concentration to a lower concentration.
• Graham’s Law: The lower the density of the gas the more diffusible the gas.
• Henry’s Law: The higher the partial pressure of a gas the quicker it will dissolve in a liquid.
Fick’s law of Diffusion
• Fick’s: the rate of diffusion of a gas in a gaseous medium is proportional to the gradient of their concentration, the surface area available for diffusion, and inversely proportional to the thickness of the membrane.
• The higher the concentration of the gas the quicker it dissolves.
Fick’s law of diffusion

Figure 1-14 Fick’s law of diffusion

Pre-class Survey!
• In mmHg, what is the pressure exerted by water in air @ 37’C?
• In mg/L, What is the absolute content of water vapor in air @ 37’C?
• What is the Cylinder Color for Oxygen?
• What is the Cylinder factor of an E tank?
Fluid Mechanics
• Laminar flow: “smooth flow” page 18 fig.1-5
• Viscosity of the gas
• Length of the tubing
• Turbulent flow: “rough flow” chaotic disorderly pattern or layers. ↑velocity +
• Transitional flow: mixture of laminar and turbulent flows.
Poiseuille’s Law (Laminar flow)
• Driving pressure plus resistance to flow
• Viscosity of the fluid/gas
• More viscous the greater the pressure needed
• Length of the tube
• Longer the tube greater the pressure needed
• ↓ radius by ½ will ↑ resistance by 16 times
• Smaller the radius the greater the pressure needed
• Reynolds’s number: Turbulent flow occurs when Reynolds’s number exceeds 2000.
Bernoulli Principle
• Bernoulli’s: as the forward velocity of a gas (or Liquid) moving through a tube increases, the lateral wall pressure of the tube will decrease.
• Drop in lateral fluid pressure is directly related to the increase in fluid velocity.
• Law of Continuity: fluids velocity varies inversely with x-sectional area
Venturi Principle
• The lateral pressure drop that occurs as the fluid flows through a constriction in a tube can be restored to the pre-constriction pressure if there is a gradual dilation in the tube distal to the constriction.
• This also helps to prevent turbulent flow.

Entrainment port

Figure 1-17 The Venturi principle

Coanda Effect
• Coanda Effect: “wall attachment phenomenon”
• A wall placed next to a jet stream of gas creates a low-pressure vortex or separation bubble. The gas stream tends to bend towards the wall. (Page 332 figure 11-21)