Module 3 Section 4 (Lung Volumes)

Question 1

Describe the different lung volumes and why they are important.

Answer 1

Tidal volume (VT):
- The volume of air entering or leaving the lung during a single breath.
- At rest, this is
typically around 500 ml.

Inspiratory reserve volume (IRV):

• The extra volume of air that can be maximally inspired above the resting tidal volume.
• At rest, this is typically around 3000 ml.

Inspiratory capacity (IC):

• The maximal volume of air that can be inhaled starting from the end of a normal expiration at rest.
• This value is typically 3500 ml (VT + IRV).

Expiratory reserve volume (ERV):

• The maximal volume of air that can be expelled starting at the end of a typical tidal volume.
• At rest, this is typically around 1000 ml.

Residual volume (RV):
- The volume of air remaining in the lungs after maximal expiration.
- At rest, this is
typically around 1200 ml.
- This volume cannot be directly measured by spirometry, but rather indirectly by inspiration of a tracer gas such as helium.

Functional residual capacity (FRC):

• The volume of air in the lungs at the end of normal passive expiration.
• This value is typically around 2200 ml (FRC = ERV + RV).

Vital capacity (VC):

• The maximum volume of air that can be expelled during a single breath following a maximal inspiration.
• This value is typically around 4500 ml (VC = I RV + VT + ERV).

Total lung capacity (TLC):
- The maximum volume of air the lungs can hold.
- This value is typically
around 5700 ml (TLC = VC + RV).

Forced expiratory volume in one second (FEV1):

• This is similar to TLC but is derived from only the first second of expiratory effort.
• This value is normally expressed as a ratio (FEV1 / FVC) or converted to a percentage.
• At rest, this value is typically around 80%.

~Look at chart on slide 2~

Question 2

Describe how lung volumes are affected in obstructive and restrictive lung diseases.

Answer 2

Obstructive Lung Disease:
- Normally, FEV1 = 80%.
- In a person with an obstructive lung
disease, they cannot exhale as much so their FEV1 is lower.
- B/c of this, the FRC and RV are > but the VC is

Question 3

Using the formula for minute ventilation, make an argument as to whether it is better to increase frequency of breathing or tidal volume in order to increase ventilation.

Answer 3

In short: to have any ventilation of the alveoli, tidal volume has to be > than the anatomical dead space. B/c of this, ventilation is more efficient with “deeper” breaths than a faster
ventilation rate.

Some of the inspired air remains in the airways and never reaches the
alveoli due to the anatomic dead space.

The dead space volume has important consequences for alveolar ventilation.

• If the volume of gas a person breathes in with each breath (the tidal volume) is the same as the volume of the dead space, then the alveolar ventilation must be zero.
• In other words, all the inspired gas stays in the anatomic dead space.

To have an effective alveolar ventilation (in terms of gas exchange), tidal volume must exceed dead space volume.
- It would seem, therefore, that the ideal breathing pattern to
maximize alveolar minute ventilation is one in which an individual uses a slow deep breathing pattern, when tidal volume is much greater than dead space volume.

~Check chart on slide 9~

Question 4

Describe what is meant by the “work” of breathing.

Answer 4

Work of breathing is the energy expended to inhale and exhale a breathing gas.

During normal quiet breathing, the inspiratory muscles overcome the elastic recoil of the lung and
airway resistance.
- Expiration is passive using the lungs recoil.
- Normally the lung is compliant and airway resistance is low so very little energy, less than 3% of total body energy, is expended during quiet breathing.
- The tidal volume and respiratory rate are optimized to minimize the work of breathing.

Low respiratory rates:

• At lower respiratory rates, in order to maintain alveolar ventilation, the tidal volume must increase.
• Increasing the tidal volume means the inspiratory muscles are working harder, the elastic work of the lung is higher.

High respiratory rates:
- In contrast, when we increase respiratory rates, the tidal volume can decrease, which reduces the elastic work of the lung, but b/c you are now moving more air, the flow-resistive work of the lung increases.

Question 5

What is a spirometer?

Answer 5

A spirometer is a device that measures the volume of air breathed in and out, and records the readings as a spirogram.

Spirometry cannot determine all of the lung volumes and capacities (the sum of two or more lung volumes) but it can determine the following measurements:

• VT
• IR&V
• IC
• ERV
• RV
• FRC
• VC
• TLC
• FEV1

Question 6

What happens if a person is suspected of having pulmonary problems?

Answer 6

They will be sent for spirometry and an

assessment of dynamic lung function

Question 7

~Look at slide 4 chart~

While you match each acronym to its appropriate location on the graph, try to recall what each stands for
and its significance:
- ERV
- FRC
- IC
- IRV
- RV
- TLC
- VC
- VT

From left to right: 
1) 
2) 
3) 
4)
5)
6)
7) 
8)

Answer 7

From left to right:

1) VT
2) IRV
3) IC
4) ERV
5) RV
6) FRC
7) VC
8) TLC

Question 8

True or false: during pulmonary function testing, it is more common to use expiratory data than inspiratory data.

Answer 8

True

Question 9

What is anatomical dead space?

Answer 9

The volume of the airways that represents the inspired gas that is unavailable for exchange with pulmonary capillary blood.

Question 10

Discuss how the alveolus changes during inspiration and expiration.

Answer 10

The amount of gas breathed in 1 minute is called the minute ventilation and is calculated by the
following equation:
Tidal Volume (VT) x Respiratory Frequency (f) = Minute Ventilation (VE)

1) At rest, the tidal volume is 500 ml and ventilation rate is 12 breaths/minute, so the minute ventilation
is 6 L/min.
- However, this does not represent the amount of ventilation available for gas exchange b/c of anatomical dead space.

2) Now, when we exhale the tidal volume of 500 ml, only 350 ml of air is expelled and again 150 ml of
air is in the airways.

3) What you should be able to recognize is that with each breath you are re-breathing the air of the anatomical dead space.

Question 11

Using what you have learned so far regarding the work of breathing and pulmonary diseases, what do you think would happen to tidal volume and respiratory frequency in the case of COPD? What about exercise?

Answer 11

COPD = increased resistance

Exercise = increased need for ventilation

Question 12

The work of breathing is increased during four conditions. What are they?

Answer 12

Decreased Compliance:

• When pulmonary compliance is decreased, the tidal volume decreases and the respiratory rate
  increases.
• An example is pulmonary fibrosis, in which more work is required to expand the lungs due to scarring of lung tissues.

Increased Resistance:

• The work of breathing is also increased when airway resistance is increased.
• This is seen during COPD and asthma when more work is required to overcome the increased flow resistance.
• There is a decrease in respiratory frequency, however tidal volume remains roughly the same.

Decreased Elastic Recoil:
- There is a decrease in elastic recoil leads to an increase in the work of breathing.
- This is observed in emphysema when passive expiration alone cannot expel air from the lungs so the expiratory muscles
are recruited.
- There is a decreased in respiratory frequency, however tidal volume remains roughly the same.

Increased Demand for Ventilation:

• Lastly, the work of breathing is increased when there is an increased need for ventilation.
• This occurs during exercise when there are increases in both tidal volume and respiratory rate.