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CBRC > Physical Principals of Respiratory Care > Flashcards

Physical Principals of Respiratory Care Flashcards

1
Q

Gas Pressure

A
  • All gases exert pressure
  • Tension is often used to refer to pressure exerted by gases when dissolved in liquids
    • The pressure or tension of a gas will depend upon kinetic activity
  • Gases are attracted to the surface of the earth due to gravity
    • Gravity increases the density of gases and increases the rate of molecular collisions and gas tension
    • This explains why atmospheric pressure decreases with altitude
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2
Q

Atmospheric Pressure

A

Pressure exerted by gases in the atmosphere

The closer to the surface of the earth the higher the atmospheric pressure

Sea Level=760 mmHg

Calgary=670 mmHg

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3
Q

Mercury Barometer

A

The mercury barometer is the most common measure of atmospheric pressure

A column of mercury is open to a reservoir of mercury; the mercury in the column will try to return to the reservoir dur to the force of gravity. Atmospheric pressure will act upon the reservoir and oppose the force of gravity causing the mercury to move back up through the tube

The height of the mercury column represents the downward force of atmospheric pressure and is measures in inches or millimeters

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4
Q

Torrs

A

Torrs can also be used as a unit of measure

At sea level 1 torr equals 1 mmHg

A pressure reading of 772 mmHg is the same as 772 torr

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5
Q

Aneroid Barometer

A

The aneroid barometer measures the atmospheric pressure by equilibrating the atmospheric gas pressure with a mechanical force, or the expansion/compressive force of an evacuated metal container.

The aneroid barometer is a sealed, evacuated metal box with a spring and gear mechanism attached to an indicator dial. Atmospheric pressure pushes on the metal box, activating the spring mechanism moving the indicator dial to the corresponding pressure

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6
Q

Strain-Gauge Pressure Transducers

A

In this device a pressure change will expand and contract a flexible metal diaphragm which is connected to a electrical wire

The physical strain on the diaphragm changes the amount of electricity flowing through the wires

By measuring the change in electrical voltage we indirectly measuring pressure

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7
Q

Bourdon Gauges

A

Combined with a flow meter used on gas tanks

Measuring much psi in a tank and how much is coming out

When full every tank will reach 2200 psi regardless of the size of the tank

Accuracy is highest at high pressure

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8
Q

What types of pressure would we measure with a column of water (cmH2O)

A

1 atmosphere is ~1034 cmH20 high, that’s as tall as a two story building, not all that practical for high pressure readings

A water column (cmH2O) is used for pressures in the lungs (Peak and PEEP) – very small numbers 5-50cmH2O – much more manageable

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9
Q

What types of pressure would we measure with a column of mercury

A

Mercury is 13.6 times denser than water so using mercury to measure pressures that are larger is better because it is easier to read for the clinical measurements we need.

A mercury column (mmHg) is used for vascular pressures (BP 120/80) – using cmH2O would create even larger numbers, not feasible to work with clinically

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10
Q

Hydrostatic Pressure

A

Pressure in non moving liquids

The greater the height of a liquid, the greater the pressure

Pressure is greatest at the bottom

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11
Q

Pressure in Liquids is Porpotional to 3 Things

A

1) Height of the liquid (depth)
2) Density of the liquid (weight per volume)

Density of water= 1000 kg/ or 1000 g/L

3) Gravity

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12
Q

Pressure in Liquids Calculation

A

Pressure in Liquids=Height x Density x Gravity

It is important to note that this equation only works when fluids are not moving

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13
Q

Gauge Pressure

A

Will not take atmospheric pressure into account

Meaning we haven’t accounted for the column of air around the earth that is also putting pressure on that object

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14
Q

Absolute Pressure

A

Does takes atmospheric pressure into account

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15
Q

Work

A

The application of a force over a given distance

It is important to remember that the distance an object moves will only be considered work if it is in the same direction that the force is being applied

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16
Q

Work Calculation

A

Work (J)=Force (N) x Distance (m)

1 Joule (J)= 1 Newton acting on 1 kg to move it 1 meter

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17
Q

Pascal’s Principals

A

Any change in a pressure in anenclosedfluid is transmitted undiminished to all parts of that fluid and to the walls of the container

This is because the pressure of a liquid will equally act in all directions

Liquid pressure depends only on the height (h) and not on the shape of the vessel or the total volume of liquid.

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18
Q

Hooke’s Law

A

Hooke described the properties of elastic recoil

A material is said to be elastic if it will regain its length or shape after the removal of the force that caused the material to change length or shape

Springs are said to be compressed or extended

Ex. The human chest wall acts as a spring, acting to expand the thoracic cavity.The lung tissue itself is acting to reduce the volume of air in the lung. These two forces are opposing one another with one pulling in and one pulling out. At the end of exhalation, these two forces will be at equilibrium

After equilibrium is reached, the lungs continue to pull in, causing the chest wall “spring” to react and begin to pull the chest out resulting in air entering the lungs. As some point, the lungs begin to react and move to pull the chest wall in causing exhalation to begin.

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19
Q

Elastic Limit

A

Each material or object will have a limit that it can be changed above which it will not return to normal

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20
Q

Hooke’s Law Calculation

A

Mathematically, Hooke’s Law looks like: F = kx

F = deforming force

k = proportionality constant

x = amount of stretch

We can see that if the distorting force is doubled, then the amount of stretch is also doubled, to a certain limit.

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21
Q

Archimedes’ Principal

A

A body, immersed in fluid is buoyed up by a force that is equal to the weight of the fluid that has been displaced by that body. This means that in order for an object to float, the weight of the object is not the main concern it is the weight of the water that has been displaced by the object that will determine whether or not it will be able to float. In order for a boat to float it has to displace more water than the weight of the boat itself

Liquids exert a buoyant force due to the fact that the pressure below a submerged object will always exceed the pressure above it

This difference in pressure will create an upward supporting force

Gases can also can have a buoyant force that will keep solid particles suspended in gases

This suspension is known as aerosols

22
Q

Urinalysis Hydrometer

A

A urinalysis hydrometer is an application of Archimedes’ Principal

How the urine analysis hydrometer works is that a glass tube of a known average density will be submerged in a liquid. The height to which it floats is calibrated as specific gravity

In some disease states there will be a change in urine composition which in turn means a change in specific gravity

23
Q

Avogadro’s Hypothesis

A

Avogadro determines that an equal volume of gas at the same temperature and pressure (STP) will have an equal number of moles and therefore moleculesIn other word 1 GMW or mole of any gas at 22.4 L at a temperature of 0 degree Celsius and a pressure of 1 ATM

Ex. 1 mole of oxygen (GMW = 32g) will occupy 22.4 L and contains 6.02 x 10^23 molecules when measured at 0 degrees Celsius and 1 ATM

This is necessary when defining the densities of gases

1 mole of gas at this volume contains 6.023 x 1023 molecules (Avogadro’s Number)

It is important to note that one mole of any gas at STP will occupy 22.4 L

Different gases will have different weights depending on their makeup and the GMW of its constituents.

24
Q

Density

A

Density is the measure of a substance’s mass per unit volume under specific conditions of pressure and temperature

Density (g/L)= Mass (GMW) / Volume (22.4 L/mole)

When look at the density of a gas that is combined with different types of gases we can use the following formula

[GMW (gas #1) * %] + [GMW (gas #2) * %]

22.4 L/mole

25
Q

Specific Gravity

A

Specific gravity is the ratio of density of one fluid compared to the density of a reference substance

Specific Gravity is a relative term

When looking at a gas’s specific gravity it will be relative to air at 1.28 g/L

Specific gravity is a unit less number

The normal SG of urine is ~1.001 to 1.035

26
Q

Gas Specific Gravity

A

Gas Specific Gravity=Density (g/L) / 1.28 g/L

27
Q

Liquid Specific Gravity

A

When looking at a liquid’s specific gravity it will be relative to water at

Liquid Specific Gravity=Density (g/L) / 1000 g/L or 1000 kg/m3

28
Q

Law of Mass Action

A

When two or more chemical substances react, one or more substances different from the original will form

A + B ⇔ C + D

As the arrow suggests the reaction is completely reversible

There is a definite relationship that exists between the speed and rate of the reaction and the quantity or concentration of the products

Other factors that will also play a role includes the chemical nature of the substance, the presence of a catalyst, and temperature

The rate of reaction is directly proportional to the concentration of the reactants.

29
Q

Hydrolysis Equation

A

A practical example in the body of the Law of Mass Action is the Hydrolysis Equation

H2O + CO2 ↔ H2CO3 ↔ H+ + HCO3-

This equation will reach equilibrium at some point

Not all the content of any part will disassociate fully.

It is completely reversible. The equilibrium can be shifted in either direction with the addition of parts.

30
Q

Adding CO2 to Hydrolysis Equation

A

Adding CO2 to the equation pushes it to the right. This will increase [H+] and therefore ↓ pH. This can occur from the following

Ex. Hypoventilation, COPD, renal failure, fever, etc.

31
Q

Adding Bi-Carb to the Hydrolysis Equation

A

Adding bi-carb will push the equation to the left nullifying [H+] and increasing pH and eventually increasing CO2as well. This can occur from the following

Ex. Kidneys retaining bicarbonate due to chronic condition, certain acute conditions that result in the use of the bicarbonate drip (need to make sure there is adequate ventilation provided in this case

32
Q

Gas

A

Weak attractive forces which results in a lack of restriction in their movement

There is a rapid random motion meaning their will be frequent collisions

Gas is a fluid meaning they have the ability to flow

Gases are very easy to compress and expand

Gases have the greatest amount of kinetic energy and the least amount of potential energy

Gases exist at temperatures above the substance’s critical temperature

33
Q

Vapors

A
  • A vapour is the gaseous form a substance that is below its boiling point and/or critical temperature
    • Ex. Water vapor in the lungs, clouds
  • Most gases that we use as RTs will be above their boiling points
    • Above the boiling point, pressure will have to be added to return the gas to its liquid form until the critical temperature is reached
    • Ex. CO2and N2O
34
Q

A Vapor and Gas Pressure

A

A vapor will exert gas pressure just the same as a true gas

Vapor pressure will increase with temperature

A decreased temperature is known as a dew point

Head pressure is the pressure on the surface of a liquid

35
Q

Vapor Pressure

A

The force the molecules exert as the hit the surface of a liquid and escape into the gaseous phase

When vapor pressure is equal to atmospheric pressure their will be rapid boiling

This is very powerful and can be explosive

36
Q

Solids

A

Solids will maintain their shape due to their strong attractive forces this means that they are not easy to compress

These forces are known as Van der Waal forces

Solids have the greatest amount of potential energy and the least amount of kinetic energy

The molecules in solids have the shortest distance to travel unil they collide with one another

37
Q

Liquids

A

Still have strong attractive forces that create a fixed volume but molecules are able to move more feely than solids which is why they take the shape of their containers

They have the ability to flow which I s why they are considered to be fluids

Like solids, they are still quite dense and not easy to be compressed

38
Q

Phase Changes

A

The physical state of any substance is determined through its relation to kinetic energy and potential energy

Exothermic Reaction-Releases energy

Endothermic Reaction-Absorbs Energy

At the melting point of ice will begin to change into it’s liquid form

A full change into liquid for requires additional heat, this additional heat will change the state of water but not an immediate change in temperature

This extra heat that is needed is known as the latent heat of fusion

39
Q

Boiling

A

Boiling: For each substance there is a temperature at which the substance will change from a liquid to a gas

The boiling point of a liquid is the temperature at which vapor pressure will equal/exceed the atmospheric pressure.

When atmospheric pressure is low liquid molecules will escape more easily and boiling will occur at a lower temperature . This means that the boiling point of a gas will decrease with an increased elevation

40
Q

Condensation

A

Condensation is the reverse of boiling

Condensation is giving heat back into the surrondings

41
Q

Vaporization

A

Vaporization: heat comes from the surroundings

42
Q

Evaporization

A

Evaporization is a form of vaporization where heat is taken from the air surrounding the liquid and cooling the air

When water (or other substances) undergo a phase change from a liquid to a gas bellows its boiling point it is called evaporation. This will occur when we add enough kinetic energy.

The rate of evaporation will increase when there is a increase in temperature, surface area, or a decrease in pressure

43
Q

Latent Heat of Vaporization

A

The energy that is required to vaporize a liquid is known as the latent heat of vaporization

This is the number of calories that are required to vaporize 1g of a liquid at its normal boiling point

44
Q

Sublimation

A

When a solid changes directly to a gas it is called sublimation

45
Q

Condensation and Evapoation

A

Both evaporation and condensation is very important in regards to breathing, as there is a delicate balance between evaporation and condensation that is needed so that the airway does not dry out and become irritated.

Mechanical ventilation will bypass the normal body processes that add heat and humidity into inspired air, which will compromise the balance between condensation and evaporation

46
Q

Critical Temperature

A

The highest temperature at which a substance can exist as a liquid when under a specific pressure

Above this temperature the kinetic activity will be so great that the attractive forces of the substance are not enough to keep it a liquid

A true gas such as O2will have a critical temperature that is so low it can be store in room temperature without turning in to a liquid. In contrast a vapor is the gaseous state of a substance coexisting with its liquid or solid state at room temperature and pressure

This is why molecular water is referred to as water vapor

A gas can be liquefied by being cooled to below it’s boiling point or by being cooling to less than its critical temperature and being compressed

The more a gas is cooled below its critical temperature the less pressure that is needed to liquify it

However under no circumstances can pressure alone liquify a gas that exists above its critical temperature

Any gas with a critical temperature above ambient should be able to be liquefy simply by having pressure applied

Both CO2 and N2O have critical temperatures above normal room temperature

This means that both gases can be store as liquids when under pressure, usually strong metal containers

47
Q

Critical Pressure

A

The pressure that is needed to maintain equilibrium between the liquid and gas phase of a substance

It is the force required to change a gas to a liquid when as critical temperature

48
Q

critical point of a substance

A

Together the critical pressure and critical temperature represents the critical point of a substance

49
Q

Triple Point

A

The set of circumstances needed to allow a substance to exist simultaneously as a solid, liquid, and gas

This happened with water at about 0.0006 atm and near 0 degrees Celsius

50
Q

Bourdon Guage

A

Flowmeter is a pressure gauge calibrated in Lpm

UNCOMPENSATED FOR BACK PRESSURE-Meaning that when there there is back pressure the guage will read higher than what the patient is receiving

As pressure enters there will be a tube that straightens out indicating the pressure

Not position dependant

Obstruction to flow will result in back pressure

CBRC (20 decks)

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