Respiration VII

Question 1

During inspiration, what happens to the diaphragm, the chest wall, the lungs, and the pleural space pressure?

Answer 1

The diaphragm contracts, the chest wall is pulled open, and this creates a more negative pleural pressure that causes expansion of the lungs.

Question 2

How does the alveolar pressure compare to atmospheric pressure during inspiration? How does this affect air flow?

Answer 2

When the lungs get pulled open, the alveolus gets larger and the pressure inside decreases. The alveolar pressure is now lower than atmospheric pressure. This pressure gradient causes air to flow from outside to inside the alveolus.

Question 3

How does the alveolar pressure compare to atmospheric pressure during expiration? How does this affect air flow?

Answer 3

During expiration, the brain tells the muscles to stop contraction. They relax and ribcage recoils downwards, which increases the pleural pressure (becomes less negative). This will allow the lungs to recoil down. This will increase the alveolar pressure above atmospheric pressure. Air will therefore flow outwards.

Question 4

What is the formula for air flow during respiration?

Answer 4

Flow = (Palv - Patm)/R

Question 5

Is the flow of air coming into the lungs positive or negative? And for air leaving the lungs?

Answer 5

The air going in is a negative flow and the air going out is a positive flow (because of the formula).

Question 6

Describe how the following vary over the course of inspiration:
a) Intrapleural pressure
b) Lung volume
c) Alveolar pressure
d) Air flow

Answer 6

a) As inspiration proceeds, the lungs fill with air, increasing the tidal volume. The increase gradually drops off as the pressure gradient between atmopsheric and alveolar air decreases.
b) Intrapleural pressure decreases as the thoracic cage moves out.
c) Alveolar pressure decreases initially due to the increase in volume of the lungs, then increases again as they fill with air.
d) Air flow is negative as it flows into the alveoli and comes back up as they fill and the pressure gradient decreases.

Question 7

Describe how the following vary over the course of expiration:
a) Intrapleural pressure
b) Lung volume
c) Alveolar pressure
d) Air flow

Answer 7

a) Intrapleural pressure climbs back up as the thoracic cage comes back down.
b) Lung volume drops as air leaves the lungs due to the compression of air in the alveoli.
c) Alveolar pressure decreases due to the drop in intrapleural pressure, as the lungs can recoil and the volume of the alveoli decreases.
d) Air flow is positive and climbs up, peaks, and comes back down to zero as the lungs empty.

Question 8

At the end of inspiration, how does Palv compare to Patm?

Answer 8

They are equal to one another (there is no pressure gradient), which is why air flow stops.

Question 9

At the end of expiration, what is the value of air flow, Palv, and Ppl?

Answer 9

Air flow is 0, Palv is 0, and Ppl is back to its resting pressure of -5 cm H2O.

Question 10

Changes in pleural pressure during inspiration and expiration depend on what two factors?

Answer 10

1. Contractions of the respiratory muscles
2. Airway resistance

Question 11

How does airway resistance affect the pleural pressure change during inspiration?

Answer 11

During inspiration, the real intrapleural pressure is lower than the theoretical one to counteract airway resistance. The opposite is true of expiration.

Question 12

How does airway resistance affect the pleural pressure change during expiration?

Answer 12

The real intrapleural pressure is higher (less negative) and greater in magnitude than the theoretical intrapleural pressure in order to counteract airway resistance.

Question 13

What is the formula for the resistance of the airways to gas flow?

Answer 13

Raw = (Palv - Pao) / Flow

Question 14

How does airway diameter affect resistance?

Answer 14

A large diameter airway can carry a large flow for a given pressure difference and so has a smaller resistance than a small diameter airway

Question 15

How does asthma affect respiration?

Answer 15

In asthma, airway resistance increases because it causes the constriction of smooth msucle, which prevents the movement of air. Sometimes, there can be mucous that further decreases the lumen of the airway as well.

Question 16

Describe the graph showing the flow-volume curve of air for varying levels of respiration effort.

Answer 16

The ascending portion varies depending on the level of effort put in, but the descending portion is independent of effort because of the compression of the airways by intrathoracic pressure.

Question 17

Explain why the descending portion of the flow-volume curve is always the same no matter the respiration effort.

Answer 17

During forced expiration, the pressure in the pleural space goes positive and is greater than the pressure in the airways. This creates a negative transmural pressure in airways. So, the airways collapse. This means that no matter how hard you try, you can’t breathe out air any faster.

Question 18

True or false? Pleural pressure is always negative. Explain.

Answer 18

False. It is always negative EXCEPT during forced expiration, where it goes as positive as +30 because of the effort of the expiratory muscles.

Question 19

Compare the pressure of the pleural space, alveoli, and transmural pressure during:
a) Pre-inspiration
b) During inspiration
c) End of inspiration
d) Forced expiration

Answer 19

a) Before inspiration, Paw = 0, Ppl = -5 cm H2o
b) During inspiration, Ppl = -7 cm, Paw = -2
c) At the end of inspiration, Paw = 0 and Ppl = -8. Intramural pressure = +8
d) During forced expiration, Ppl = +30, Plv = +38, transmural pressure = -11. This causes the airways to close.

Question 20

Describe the lung volume-flow curve for normal individuals (incl. highs and lows)

Answer 20

Range: volume of 2.5 - 7, peaks high at around 7 and falls sharply.

Question 21

Describe the lung volume-flow curve for individuals with restrictive diseases (incl. highs and lows). Explain why it looks this way.

Answer 21

A subject with a disease like pulmonary fibrosis, which is a restrictive disease, causes stiff alveoli, making it harder to inflate the lungs (recall). If a subject with fibrosis breathes in to max capacity, the compliance of the lungs is low so the total lung capacity is low. Then, if they breathe out as hard as they can, the maximum flow is low compared to a normal subject. This is because the max flow is low, so there’s less driving pressure.

Question 22

Give an example of a restrictive pulmonary disease and how it affects the lungs.

Answer 22

Pulmonary fibrosis. It causes stiff alveoli, making it harder to inflate the lungs.

Question 23

For the same lung volume how does expiratory flow compare between normal individuals and individuals with a restrictive lung disease?

Answer 23

For the same lung volume, the subject with fibrosis has a higher flow than a normal subject. This is because their lungs naturally want to collapse, meaning that air will leave faster.

Question 24

Describe the lung volume-flow curve for individuals with obstructive diseases (incl. highs and lows). Explain why it looks this way.

Answer 24

Here, the lungs are very compliant. The total lung volume is extremely high compared to normal subjects. When they are asked to breathe out as hard as they can, the increase in flow is very slow as a function of the expired flow and the maximum flow is low compared to the normal subject. Because these lungs have no recoil, it is much harder to breathe out. When they breathe out to their residual volume, there is much more left over than in normal subject.

Also note the little scoop on the emphysema patient curve.

Question 25

Give an example of an obstructive pulmonary disease and explain how it affects the lungs.

Answer 25

Emphysema is an obstructive pulmonary disease. It causes the lungs to be very compliant, so the total lung volume is high and the lungs have on recoil. They therefore are left with a lot of air in their lungs after expiration and they can’t breathe in very much air.

Question 26

Name the 7 steps of inspiration in order.

Answer 26

1. Diaphragm and intercostal muscles contract
2. Thoracic cage expands
3. Intrapleural pressure becomes more negative
4. Transpulmonary pressure increases
5. Lungs expands
6. Alveolar pressure becomes subatmospheric
7. Air flows into the alveoli

Question 27

Name the 8 steps of expiration.

Answer 27

1. Diaphragm and external intercostal muscles stop contracting
2. Chest wall moves inwards
3. Intrapleural pressure goes back towards preinspiratory value
4. Transpulmonary pressure goes back towards preinspiratory value
5. Lung recoil towards preinspiratory volume
6. Air in lungs is compressed
7. Alveolar pressure becomes greater than atmospheric pressure
8. Air flows out of the lungs

Question 28

How does exercise affect tidal volume and breathing frequency?

Answer 28

• When exercise starts, both tidal volume and frequency increase proportionally.
• However, at some point tidal volume plateaus.

Question 29

Explain why tidal volume and breathing frequency change the way they do during exercise.

Answer 29

Tidal volume plateaus eventually because lung compliance decreases at very high lung volumes.

Thus, high ventilatory rates during hard exercise are due to incremental increases in breathing frequency.

Question 30

How does exercise affect inspiratory and expiratory times?

Answer 30

Because of the increased breathing frequency, inspiratory and expiratory times decrease during progressive exercise, but expiratory times fall relatively more than inspiratory time.

Question 31

How do peak inspiratory flow rate and peak expiratory flow rate change during exercise? Explain why.

Answer 31

Peak expiratory flow rate increases more than peak inspiratory flow rate. This is because the time of inspiration at rest is already slower than the time of expiration at rest, so expiration will increase faster.

Question 32

Is minute ventilation believed to limit aerobic performance? Explain why or why not.

Answer 32

No, because since tidal volume can increase more then perfusion during exercise, Ve/Q will always be more than 1.

Question 33

Is alveolar surface area believed to be a limiting factor in aerobic performance? Explain why.

Answer 33

Not, because the alveolar surface area only holds around 4% of our 5L of blood during maximal exercise, but it has the capacity to hold all of it.