Decoursey Ventilation and Gas Exchange

Question 1

What are the two types of ventilation

Answer 1

Minute ventilation

Question 2

Define minute ventiliation
Equation

What does it contribute to?

Answer 2

Amount of air moved in and out the lung in one minute

Ve= Frequencyx Tidal Volume

Contributes to WORK

Question 3

Define alveolar ventilation
Equation?
What does it contribute to?

Answer 3

total air moved into the respiratory zone per minute

Va= Frequency x (Vtidal-Vdead space)

Contributes to gas exchange.

Question 4

Explain the two types of dead spae

Answer 4

1. Anatomic dead space- air that doesn’t reach alveoli so can’t exchange with blood, its composition is unchanged.

It’s the volume of the conducting airways

2. Phsiologic dead space- should be the same as anatomic dead space, but in disease we add the portion of the lungs that doesn’t participate in exchange. It’s a functional measurement

Question 5

Why does Bohr equation work?

What happens in disease?

Answer 5

We are trying to physiologic dead space. the air entering the lung has ~0CO2 while PCO2 in the alveoli is about 40.

We can measure the ratio of the two from an expired breath (has both because some if from dead space) and that’ll tell you fraction of dead space.
IN disease the ratio would increase because some of the lung acts like dead space

Question 6

What is the best way to breath to get the high alveolar ventilation

Answer 6

Deep breaths. Dead space is constant so beyond dead space volume the rest is exchanged.

Shallow breaths would proportionally have a lot in the dead space

Question 7

How can alveolar ventilation change when frequency and tidal volume are constant?

Answer 7

in disease there can be an increase in physiologic dead space so the patient gets less benefit from breathing

Question 8

Anatomic dead space rule of thumb

Answer 8

It’s really hard to measure but generally the volume in ml is equal to the persons weight in pounds

Question 9

Equation for work

Answer 9

Work= forcex distance
Work= Pressure x volume

Question 10

What is the a static lung working against?

Dyanmic?

faster dyanmic?

Answer 10

Elastic recoil. Our working lung is actually dynamic.

Dynamic we have airway resistance in addition to elastic recoil

Faster dynamic- we have increased airway resistance because were are forcing air to move faster

Question 11

What happens to the respiratory muscles in a person with emphysema?

Answer 11

Moderate exercises increases the work done by the lungs to that of a normal marathon runner taking almost all of their respiratory muscle power

Question 12

At constant alveolar ventilation decreasing frequency does what to tidal volume?

Answer 12

Increases the tidal volume although this increases the dead space (because the airways are stretched more), deep breathing maximizes ventilation alveolar

Question 13

What are you working hard against at low frequency?

Answer 13

Elastic recoil. Low frequency means the tidal volume is higher so the lungs have to stretch beyond the high compliance region (to the flatter part of the Pv volume curve)

Question 14

At high frequency what work is high?

Answer 14

Work against airway resistance.
Respiratory muscles have to contract harder to get air in and out faster… need a higher pressure gradient.

turbulece also becomes a factor at high frequency demanding even more work

Question 15

Summarize effects of low, middle and high frequenecy

Answer 15

Low- high tidal volume- more work
MIddle- minimal work
High- high tubulence/more contraction for faster movement and gradient- more work

You can get the same alveolar ventilation with all three types of frequency but work increases when you move away from the middle breathing (15-20/min)

Question 16

Why is middle breathing effective

Answer 16

At deep breaths (low frequency) elastic resistance is high but resistance is low

At shallow breaths (high frequency) elastic resistance is low but turbulence and airway resistance is high.

Middle breathing requires the lowest total work against both forces

Question 17

What is the most efficient way to breath with emphysema? Why?

Answer 17

Less frequently. Getting air out is the problem so we minimize work by breathing with less frequency

Elastic recoil is reduce and airway resistance is increased during expiration due to dynamic compression

Question 18

Efficient breathing with fibrosis?

Answer 18

Elastic recoil is increased so its harder to inflate lungs so increase frequency and reduce tidal volume

Question 19

Composition of Earths atmosphere

Answer 19

Nitrogen- 78%
Oxygen- 21%
Argon- 1%
CO2- almost 0

Neon helium krypton Hydrogen and Xenon are in trace amounts

Question 20

What does Daltons law state

Answer 20

the total pressure exerted by a mxture is equal to the sum of all the pressures that would be exerted if the gases were alone.

Question 21

Why is partial pressure important?

Answer 21

because it applies to gases in liquid and in gases and gases always go down their pressure gradient

Question 22

What is the definition of partial pressure

Answer 22

Bolded-

At equilibrium gas dissolves into the liquid from gas at the same rate that gas evaporates from liquid to gas

Question 23

Explain how to find parial pressure

Answer 23

total pressure x fraction that has occupies

Question 24

What two factors determine the amount of a gas dissvoled

Answer 24

Solubilty x Partial pressure= Concentration of gas=Henrys Law

Question 25

Solve for Partial pressure of O2 and Nitrogen

Answer 25

760 x .21= 160 torr= PO2

760x .78= 600 torr= Pnitrogen

Question 26

Partial pressure is not equivalent to content.. why?

Answer 26

The partial pressure is an indiction of how much gas is present but you have to consider solubility of the gas.

Henry law suggest Concentration= Partial pressure x solubility

Question 27

Explain what happens to partial pressure throughout the system

Answer 27

The total pressure remains constant throughout the respiratory system. Nitrogen remains fairly constant
CO2- Significantly higher throughout the body then ambient
O2- decreases from ambient to the tissues
H20- ambient (5.7) reaches 47 almost immediately in the trachea

Question 28

Explain what happens to H20 when it enters the body

Answer 28

1. Body is 100% humidity (47 torr water vapor at 37C)
2. Ambient air has less (dependent on humidity)
3. When we inspire air we humidify the air and water vapordisplaces other gases… mainly Nitrogen but also about 10 torr of O2

Remember we’re staying at 760 total

Question 29

Why does fog condense when we breath out and it’s cold

Answer 29

When we exhale the breath is warmer and has 47 torr of water vapor and the windshield is much lower temp. As temp of the air decreases and it’s capacity to contain water vapor decreases so it makes fog.

Question 30

What does the air blood barrier consist of>

Answer 30

Alveolar epithelial cells
CApillary endothlial cells
Interstitial space

All < 1um

This structure is key to diffusion

Question 31

What Ficks Diffusion Law

Answer 31

Jgas(diffusion)= (Dgas x Areax concentration gradient)/ distance

For gas we have to consider concentration in terms of partial pressure but we need to consider solubility.

So J=D x A X solubilty x delta Partial Pressure/ distance

Question 32

What type of O2 contributes to the PP?

Answer 32

ONly DISSOLVED.

Once O2 binds to Hb it no longer contributes to the PP values

Question 33

Dicuss diffusion and equilibrium of O2

Answer 33

This happens almost immediatley and in a normal subject isn’t a problem.

takes blood PO2 about .25 seconds to equilibriate with that of air.

In disease (pulmonary edema etc) equilibrium takes much long or may never happen

Question 34

What happens in exercise to the diffusion of O2?

Answer 34

CO ouput increases by upto 5x so blood is flowing past the alveolar capillary in about .25 seconds.

Even still in a healthy lung, this is enough time because of recruitment and dilation of pulmonary vessels.

Question 35

Why do CO2 and O2 equilibriate at about the same rate but have such different pressure gradients?

Answer 35

CO2 gradient is about 5
O2 is about 60

We’re considering the gradient between tissue and alveolar
So O2 tissue- 40 Alveolar- 100
CO2 tissue- 46
Alveolar- 40

But we have to consider solubility. CO2 is 25x more soluble so that makes up for the small driving force.

Question 36

Why doesn’t alveolar PO2 and PCO2 change dramatically with each breath

Answer 36

There are changes but they are small because the FRC (and even RV) act as buffer that prevent large changes to the alveolar gases

Also staying constant meanst hat there is relatively constant/large pressure gradient

Question 37

What does Dl measure?

Answer 37

How well diffusion it occurring b/w alevolar air and the blood

Its the rate that a lung takes up O2 corrected for driving force.

Question 38

Equation for Dl

Answer 38

Dl= Flow of O2/ (PAo2-PvO2)

The driving force DOESN”T determine/change the DL. If you half the gradient then the Flow halves and the DL is constant

Question 39

Why is CO ideal for testing of how well diffusion is working>

Answer 39

It transfer from air to blood. venous CO is generally zero because it immediately binds to Hb.

Bad for a patient because it has higher affinity than O2 but good for test because nothing is the way of duiffusion

Question 40

Name a couple things that DON”T affect Dl

Answer 40

breathing faster
Larger tidal volumes
HIgher FiO2
The pressure gradient

Question 41

Alevolar Gas Equation

Answer 41

PAO2= Pinspired airO2- (Parterial CO2/RQ) + Correction factor

Question 42

What determines alveolar gas content

Answer 42

1. Ventilation (increase O2 and decrease CO2)
2. Metabolim (decrease O2 and add CO2)

Balance results in alveolar PO2=100 and PCO2= 40

Question 43

What determines Dl

Answer 43

Everything in Ficks except the driving force

Question 44

Why does increasing ventilation affect CO2 more? (metabolism is constant)

Answer 44

Alveolar O2 starts at 100 and CO2 starts at 40. Atms O2 is 150 and CO2 is 0.

When you double ventilation you can half CO2 but it’s impossible to double O2 becuase you’re starting at 100 and the air is only 150.

Question 45

What does alveolar PO2 fluctuate between

Answer 45

98-100. Very small changes because of FRC