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PHSL232 > Lecture 14 - Lung mechanics and lung volumes > Flashcards

Lecture 14 - Lung mechanics and lung volumes Flashcards

1
Q

What is occuring if Patm= 0 mmHg and Palv = 4 mmHg?

A

Air is flowing out of the lung

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2
Q

What work needs to be done in breathing?

A

Overcome elastic properties (or stiffness) of lung
Overcome airway resistance

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3
Q

What factors effect how hard is it to expand lungs?

A

• Compliance of lung
• Surfactant

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4
Q

What is lung compliance?

A

A measure of elastic property of the lung, compliance is the
inverse of stiffness

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5
Q

What is lung compliance defined by?

A

Defined as the magnitude of the change in the lung volume (ΔVL) produced by the given change in the transpulmonary pressure (ΔPtp)
CL = ΔVL ⁄ ΔPtp

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6
Q

What are the determinants of lung compliance?

A

1.Stiffness / elasticity of lung
2.Also need to overcome SURFACE TENSION at
the fluid gas interface - surfactant

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7
Q

What happens during emphysema?

A

Alveoli wall damage - big air pocket, smaller SA
“Floppy” lungs
High compliance (very stretchy)
- No effect on inspiration
Low elastic
recoil
- Requires more Energy During expiration

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8
Q

What happens during fibrosis?

A

“Stiff” lungs
Low compliance - more energy
for inspiration
High elastic recoil - No additional
energy required for expiration

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9
Q

Why is surfactant important?

A

Hydrogen/fluid attracted to each other so wants to come together. Bigger problem in smaller alveoli where things are closer.
Surfactant – reduces surface tension in alveoli

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10
Q

Where is surfactant produced?

A

alveolar type II cells

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11
Q

What is the major constituent of surfactant?

A

phospholipids

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12
Q

How does surfactant lower surface tension?

A

Reduces attractive forces between
fluid molecules lining alveoli - hydrophobic phospholipids

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13
Q

What occurs when there is a lack of surfactant/failure to produce adequate surfactant?

A

“stiff” lungs

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14
Q

Why do premature infants develop respiratory distress syndrome (RDS)?

A

Surfactant is absent in premature infants - Type II cells don’t differentiate until 34 weeks

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15
Q

In new-born RDS what happens to alveoli?

A

They become collapsed

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16
Q

Surfactant:

A

Lowers surface tension at the fluid-gas interface of the alveoli
Stabilizes the smaller alveoli, thereby preventing them from collapsing due to high pressure.

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17
Q

How is resistance to flow determined by?

A

Poiseuille’s Law
R = 8nl / πr4

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18
Q

What are important elements in airway resistance?

A

Bronchoconstriction / bronchodilation

19
Q

Where is the main area of airway resistance?

A

BRONCHI
Most of the resistance to airflow arises in the the first 6 generations of the airway. Trachea - early bronchioles

20
Q

Whys is resistance is higher in larger airways?

A

Resistance to air flow depends on the number of parallel pathways present - larger airways are are in parallel (bronchi)

21
Q

What normal condition factors affect airway resistance?

A

Lung volume
Radial traction

22
Q

How does lung volume effect airway resistance?

A

Lung volume:
- increases during inspiration (due to increase in transpulmonary pressure)
- airway radius becomes larger
- airway resistance lower
- lung expands

23
Q

How does radial traction effect airway resistance?

A

Radial traction:
Pulling of adjacent alveoli – reduces airway resistance

24
Q

What diseases affect airway resistance?

A

Asthma
Chronic obstructive pulmonary disease (COPD)
• Emphysema
• Chronic Bronchitis

25
Q

What does the pressure-volume loop tell you?

A

information on compliance of lung

26
Q

What happens during restrictive lung disease?

A

No change in airway resistance
•Lung compliance decreased, pressure-volume curve shifted to the right
• More work to overcome elastic resistance
• A more negative Pip required to move the same amount of air, increases the work of breathing

27
Q

What is an example of a restrictive lung disease?

A

Asthma

28
Q

What happens during obstructive lung disease?

A

No change in lung compliance
• Airway resistance has increased
Intra pleural pressure (mmHg) Intra pleural pressure (mmHg)
• More work to overcome non-elastic resistance, inspiration
• Similar work to overcome elastic resistance
• More work to overcome non-elastic resistance, expiration, a more positive expiratory pressure is required, expiration becomes active process
• A more negative intra pleural pressure (Pip) required to move the same amount of
air

29
Q

What are examples of obstructive lung diseases?

A

Chronic obstructive pulmonary disease (COPD)
• Emphysema
• Chronic Bronchitis

30
Q

Assertion question: Lung compliance is increased in emphysema BECAUSE
chronic emphysema increases airway resistance.

A

B. Both statements are true but are not causally related

31
Q

How can we measure lung function?

A

Spirometry
Peak Expiratory Flow Rates (PEFR)

32
Q

What is tidal volume?

A

~ 500 ml (VT or TV).
Volume of air moved in and out during normal quiet breath

33
Q

What is inspiratory reserve volume?

A

~ 3 L (IRV).
Extra volume that can be inspired with maximal inhalation - external intercostal muscles.

34
Q

What is expiratory reserve volume?

A

~ 1.2 L (ERV).
Extra volume that can be exhaled with maximal effort - internal intercostal and abdominal muscles.

35
Q

What is residual volume?

A

~ 1.2 L (RV).
Volume remaining in lungs after maximal exhalation.

36
Q

What are the different lung volumes?

A

Tidal
Inspiratory reserve
Expiratory reserve
Residual

37
Q

What are the lung capacities?

A

The lung capacities are made up of lung volumes and they are:
Inspiratory
Vital
Functional residual
Total lung

38
Q

What is inspiratory capacity?

A

maximal breath in (Vt + IRV)

39
Q

What is vital capacity?

A

~5L.
Maximal breath into out Volume of air can shift
in/out of lungs (IC +ERV)

40
Q

What is Functional residual capacity?

A

~2.4L.
Remaining volume at end of normal breath
out (ERV +RV)
Lung volume at the end of a normal expiration when there is no inspiratory or expiratory muscle contractions

41
Q

What is total lung capacity?

A

~6L.
Total volume in lungs when maximally full
= (VC + RV)

42
Q

Why is a large FRC important?

A

At all times during the breath cycle O2 and CO2 exchange can occur between alveolar gas and the pulmonary capillaries.
Prevents large fluctuations in the composition of alveolar gas

43
Q

What happens to lung volumes/capacities during restrictive diseases?

A

VC decrease
IRV decrease
ERV decrease
RV decrease
FRC decrease
TLC decrease

44
Q

What happens to lung volumes/capacities during obstructive diseases?

A

VC constant
IRV constant
ERV constant
RV increase
FRC increase
TLC increase

PHSL232 (31 decks)

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