Ventilation

Question 1

True or False: Ultimately, what is important is the amount of air-flow, which is affected by compliance and resistance.

Answer 1

True

Question 2

What is ventilation?

Answer 2

Airflow in the lung

Question 3

What is minute ventilation (VE)?

Answer 3

Volume of air-flow through the lung in one minute Minute ventilation = Tidal Volume (TV) x Breathing Rate

Question 4

What is average minute ventilation in an adult?

Answer 4

6 L 0.5 L/breath x 12 breaths/min = 6 L

Question 5

What is alveolar ventilation (VA)?

Answer 5

Volume of air-flow in alveolar space in one minute

Question 6

What is average alveolar ventilation in an adult?

Answer 6

~4.2 L

Question 7

True or False: Alveolar ventilation is the most important parameter when considering gas exchange.

Answer 7

True

Question 8

What are factors that affect alveolar ventilation (VA)?

Answer 8

1. Obstructive disease (e.g. COPD) 2. Compliance problems 3. Exercise (ventilation can increase up to 10x) 4. High altitude 5. Gravity (introduces regional variations in ventilation) Note: Generally, total alveolar ventilation (VA) is affected only by severe disease conditions.

Question 9

How does gravity cause regional variations in ventilation?

Answer 9

Alveoli near the top of the lung are weighted down by the remainder of the lung below it. So, if you have three alveoli, the top one has the greatest volume while the bottom has the smallest volume. The top alveoli is being pulled open by the weight. Vol-top-alveolus is greater than Vol-bottom-alveolus However, counterintuitively, the alveoli closer to the bottom of the lung have more ventilation than the alveoli that are near the top. This is because ventilation depends on the change in volume during breathing. Even though the alveoli near the top have a greater volume, the alveoli near the bottom have a greater change in volume during breathing. Vent-top-alveolus is less than Vent-bottom-alveolus

Question 10

About how many times more ventilation is there at the bottom of the lung than at the top?

Answer 10

2.5 times. Ventbottom / Venttop = 2.5

Question 11

How can you use the compliance curve to analyze the difference in ventilation between bottom and top alveoli?

Answer 11

In the diagram, you can see that the bottom alveolus has greater compliance than the top alveolus. The top alveolus is already at a greater volume and is less compliant because there is only so much that you can inflate an alveolus. The bottom alveoli has greater compliance and has a greater change in volume when breathing resulting in greater ventilation.

Question 12

What are the axis on the compliance curve and what does the slope stand for?

Answer 12

X axis - Transpulmonary pressure

Y axis - Alveolar/Lung volume

Slope - Compliance ( = delta V/ delta P)

Question 13

True or False: Compliance and resistance problems can also affect HOW we breathe.

Answer 13

True

Question 14

A 6 L minute ventilation can be achieved by:

Taking 5 breaths/minute with a tidal volume of 1.2 L each.

Taking 30 breaths/minute with a tidal volume of 0.2 L each

Which one of these scenarios would spend more joules of work going against resistance?

Answer 14

Taking 30 breaths/minute with a tidal volume of 0.2 L each would spend more joules of work going against resistance. At lower tidal volumes, the airways are smaller. The smaller radius of the airways results in higher resistances to overcome.

Question 15

A 6 L minute ventilation can be achieved by:

Taking 5 breaths/minute with a tidal volume of 1.2 L each.

Taking 30 breaths/minute with a tidal volume of 0.2 L each

Which one of these scenarios would spend more joules of work going against elastance?

Answer 15

Taking 5 breaths/minute with a tidal volume of 1.2 L each would spend more joules of work going against elastance. As you reach higher lung volumes, you are getting further and further away from the lung’s resting state and it takes increasingly more work to cause a change (compliance decreases at higher volumes).

Question 16

Explain this diagram

Answer 16

On the left, you have the work vs. freq-TV curves of a healthy person. You can see that the least total work can be found at about 12 breaths/min at 0.5 L tidal volume per breath. People naturally breathe at a rate that uses least work.

In an obstructive disease, the resistances in the airways are higher across the board. This makes the freq-TV of least total work around 6 breaths/min at 1 L tidal volume per breath. This means that compared to a healthy individual, an individual with bronchitis will be breathing at a slower rate with higher lung volumes. This is to compensate for the obstruction because increasing lung volume will decrease the resistance in the airways. While 6 breaths/min at 1 L tidal volume per breath is the most energy efficient point for a patient with obstructive disease to breathe at, it is still more total work than if the patient was healthy.

Question 17

True or False: Not all of the ventilated air contributes to gas exchange

Answer 17

True

Question 18

What is dead-space?

Answer 18

Volume of lung that does not engage in gas exchange

Question 19

What is anatomical dead-space? How much (%) of total lung volume is anatomical dead-space?

Answer 19

Anatomical dead-space is the airways. This makes up about 30% of the total lung volume and does not engage in gas exchange.

Question 20

What is alveolar dead-space? Give one example that could cause this

Answer 20

Alveolar dead-space is when an alveolus that normally engages in gas exchange isn’t able to. This can happen if there is an occlusion in pulmonary capillary that’s next to the alveolus (e.g. pulmonary embolism). The alveolus is still ventilated but that ventilation doesn’t participate in useful gas exchange.

Question 21

What is physiologic dead-space? Why is this important?

Answer 21

Physiological dead-space = Anatomical dead-space + alveolar dead-space

Physiological dead-space is measurable with pulmonary function tests while the individual parameters (anatomical and alveolar dead-space) are not. In real situations, you measure the physiological dead-space, make an assumption about how mcuh anatomical dead-space is present, and then you can make a decent assumption about how much alveolar dead-space is present.

Question 22

What does deadspace do to efficiency of breathing?

Answer 22

Deadspace reduces the efficiency of breathing since there is more wasted ventilation. This increases the work required to breathe.

The example used in class was that when snorkling, more deliberate breathing is necessary because the snorkel is essentially increasing the airway/anatomical dead-space. You have to breathe in more deliberately to get the ventilation down to the alveoli.

Question 23

What is total lung capacity?

Answer 23

Total lung capacity: the volume in the lungs at maximal inflation, the sum of VC (vital capacity) and RV (residual volume).

Question 24

What is vital capacity?

Answer 24

Vital capacity: the volume of air breathed out after the deepest inhalation.

Question 25

What is residual volume?

Answer 25

Residual volume: the volume of air remaining in the lungs after a maximal exhalation

Question 26

What is functional residual capacity?

Answer 26

Functional residual capacity: the volume in the lungs at the end-expiratory position

Question 27

What is tidal volume?

Answer 27

Tidal volume: that volume of air moved into or out of the lungs during quiet breathing (VT indicates a subdivision of the lung; when tidal volume is precisely measured, as in gas exchange calculation, the symbol VT or VT is used.)

Question 28

What is the average tidal volume for an adult?

Answer 28

0.5 L

(Note: at 12 breaths/min, a tidal volume of 0.5 L per breath puts you at 6L per minute which is average)

Question 29

What is forced vital capacity (FVC)?

Answer 29

Forced vital capacity: the determination of the vital capacity from a maximally forced expiratory effort

Question 30

What is FEV1.0?

Answer 30

Forced expiratory volume after 1 second (Volume that has been exhaled at the end of the first second of forced expiration)

Question 31

What calculation is used to determine the rate of airflow during expiration?

Answer 31

FEV1.0/FVC

This is a ratio between the amount of volume exhaled in one second over the total amount of volume exhaled from a maximally forced expiratory effort.

A typical value for this measurement is 0.8. This means that after 1 second of expiration, 80% of the forced vital capacity has been expelled from the lungs.

Question 32

What is a typical value for FEV1.0/FVC in a healthy person?

Answer 32

0.8

Question 33

Pulmonary fibrosis is associated with a large decrease in lung compliance. What does this do to the following factors:

1. RV
2. FRC
3. TLC
4. VC
5. FEV1.0/FVC

Answer 33

1. RV is slightly decreased
2. FRC is slightly decreased
3. TLC is decreased
4. VC is decreased
5. FEV1.0/FVC is not changed or possible slightly increased

Remember, elastance is the reciprocal of compliance. In pulmonary fibrosis, lung compliance is decreased which means elastance is increased. The forces bringing the lung back to its intrinsic equilibrium position are greater because of the increased elastance/decreased compliance.

Question 34

Bronchitis is a resistance problem (rate of airflow is decreased).

What does this do to the following factors:

1. RV
2. FRC
3. TLC
4. VC
5. FEV1.0/FVC

Answer 34

1. RV is increased
2. FRC is increased
3. TLC is unchanged
4. VC is decreased
5. FEV1.0/FVC is decreased

Remember, patients with bronchitis try to compensate for the increased resistance by breathing at higher lung volumes. At higher lung volumes, their airways are opened up which decreases the resistance. RV and FRC are increased as a result of breathing at higher lung volumes and the TLC stays the same because even though the rate is slowed down in patients with bronchitis, their total lung capacity is not changed. Another reason that TLC can stay the same is because as you increase lung volume, the resistance in the airways is decreased and the patient with bronchitis can still reach their normal TLC. The vital capacity is decreased because the total lung capacity stays the same and the residual volume is increased (TLC = VC + RV). The FEV1.0/FVC is decreased because there is increased resistance in bronchitis so expiration of volume is slowed.