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Physiology 1 > Mechanics of breathing II > Flashcards

Mechanics of breathing II Flashcards

1
Q

During inspiration/expiration, why doesn’t the movement of air instantaneously equalise the pressure gradient between the alveoli and the atmosphere?

A

There is a slight delay due to the time taken for air to move from the atmosphere to the alveoli and vice versa.

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2
Q

What are the two variables that determine airflow?

A

Pressure gradient

Airway resistance

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3
Q

Define “airway resistance?”

A

The forces generated when air flows through the airways that oppose airflow

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4
Q

What is the equation for airflow when the concept of ohm’s law is applied?

A

Airflow (V) = ∆Pressure (P)/Resistance (R)

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5
Q

What does ohm’s law suggest about the relationship between airflow, airway resistance and a pressure gradient?

A

Suggests that airflow is proportional to the pressure gradient and is inversely proportional to the airway resistance

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6
Q

What does the Hagen–Poiseuille equation state about the factors that affect airway resistance?

A

States that resistance is inversely proportional to the tube radius raised to the 4th power. Also states that resistance is directly proportional to both the the tube length and the air viscosity.

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7
Q

What is the Hagen–Poiseuille equation?

A

R = 8ηL/π r4

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8
Q

What do each of the variables in the Hagen–Poiseuille equation represent?

A 
R = Airway resistance 
η = Air viscosity 
L = Tube length 
r = Tube radius
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9
Q

What controls the lumen diameter of the airways?

A

Contraction/relaxation of the smooth muscle surrounding the airways

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10
Q

How does air normally flow through the airways?

A

Air floes in a laminar manner

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11
Q

Why does turbulent flow generate more air resistance than laminar flow?

A

During turbulent flow the air does not flow linearly and smoothly in adjacent layers like it does during laminar flow. This creates greater amounts of friction between the air and the surrounding lumen which increases resistance.

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12
Q

What are the 2 situations in which air flows turbulently through airways?

A
  1. When an individual breathes extremely hard - increased velocity causes air to move with greater turbulence
  2. When there are areas of obstruction within the airways
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13
Q

What is airway patency?

A

The state of the airways being open

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14
Q

How may airway patency be lost within an airway?

A

Inflammatory processes degrade some of the proteins that contribute to structural integrity of airway.
This means that the airways collapse when put under pressure

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15
Q

What is the effect of reduced patency of an airway on airflow?

A

Less air is able to flow through due to the radius of the lumen being a lot smaller

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16
Q

How can airway obstruction be measured in a person?

A

By using spirometry

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17
Q

Explain how a spirometry test is carried out?

A

Breathing through a spirometer the person takes the biggest breath in they can and then breathes out as fast and for as long as they can. This gives a measurement for the maximum expiration for the person.

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18
Q

What are the 2 measurements produced from a spirometer test?

A 
FVC = Forced vital capacity 
FEV1 = Forced expiratory volume in 1 second
19
Q

What calculation can b done with these 2 measurements and what does it show?

A

FEV1/FVC x 100 = % of total lung capacity an individual can exhale in the first second

20
Q

Why is the FEV1/FVC ratio used to calculate the level of airway obstruction rather than just the FEV1?

A

Because somebody with a larger lung capacity would be able to get more air of their lungs within the first second or vice versa

21
Q

What is meant by obstructive lung disease?

A

Diseases that cause narrowing (obstruction) of the smaller bronchi and larger bronchioles, often due to excessive contraction of the smooth muscle of the airways.

22
Q

What is meant by restrictive lung disease?

A

Diseases that restrict lung expansion resulting in a decreased lung volume.

23
Q

How do both obstructive and restrictive lung diseases affect speed of airflow through the airways and lung volume?

A

With obstructive lung disease the speed at which air can flow out of the lungs is reduced but overall lung capacity isn’t while with restrictive lung disease the speed of airflow through the airways isn’t affected but lung volume is reduced.

24
Q

How does an obstructive lung disease affect FVC and the FEV1/FVC ratio?

A

FEV1/FVC decreases to <70%

FVC unaffected so > 80%

25
Q

How does a restrictive lung disease affect FVC and the FEV1/FVC ratio?

A

FEV1/FVC unaffected so > 70%

FVC decreases to < 80%

26
Q

What is transpulmonary pressure and how can you calculate it?

A

The level of force acting to expand the lung.

Transpulmonary pressure (Ptp) = Alveolar pressure (Palv) – Intrapleural pressure (Pip)

27
Q

What is lung compliance and how can you calculate it?

A

𝐶𝑜𝑚𝑝𝑙𝑖𝑎𝑛𝑐𝑒 (𝐶𝐿)= Δ𝑉𝑜𝑙𝑢𝑚𝑒/Δ𝑃𝑟𝑒𝑠𝑠𝑢𝑟𝑒

28
Q

What is lung compliance actually a measure of?

A

How much expansionary force do you need to apply to the lung tissue in order to produce a certain volume change.

29
Q

Give some examples of diseases that decrease lung compliance?

A

Pulmonary fibrosis
Scoliosis
Muscular dystrophy

30
Q

Give some examples of diseases that increase lung compliance?

A

COPD (Emphysema)

31
Q

Why are the alveoli lined with fluid?

A

Allows the gas molecules to dissolve in the fluid before dissolving which increases diffusion rate

32
Q

Explain how the alveoli being lined with fluid contributes to the generation of surface tension within the alveoli?

A

Within the bubble formed by the water-air interface, the attractive force that create Hydrogen bonds between the water molecules is stronger than the attractive force between the water molecules and the air molecules. This exerts a collapsing force toward the centre of the bubble (Surface tension).

33
Q

How does the generation of surface tension within the alveoli affect alveolar pressure?

A

Causes an increase in alveolar pressure as surface tension causes area of alveoli to decrease.

34
Q

What is Laplace’s law used to calculate?

A

Calculates the amount of pressure generated by the surface tension within a bubble with a depending on its radius.

35
Q

What is the equation for Laplace’s law and what do each of the variables in the equation represent?

A 
P = 2T/R 
P = Pressure 
T = Surface tension 
R = Radius of bubble
36
Q

What would occur if you had 2 alveoli of with different radii connected to each other? Why is this the case?

A

A Pressure gradient would be created between the 2 different sized alveoli, resulting in smaller alveoli emptying into the larger one.
This occurs because the smaller alveoli will generate a greater collapsing force (surface tension) and as a result more pressure meaning the air from the smaller alveoli gets pushed out into the larger one.

37
Q

How is the respiratory system adapted to ensure that all the alveoli get filled with air despite the fact that different sized alveoli are connected to each other?

A

Alveoli contain something called pulmonary surfactant. This is a lipoprotein complex which has both both hydrophobic and hydrophilic regions.

38
Q

Explain the mechanism that allows for pulmonary surfactant to reduce surface tension within the alveoli?

A

Fact that pulmonary surfactant has both hydrophobic and hydrophilic regions means it adsorbs to the water-air interface within the alveoli. By sitting inbetween some of the water molecules it disrupts the attractive forces that causes hydrogen bonds to form between them thus reducing surface tension preventing alveoli from collapsing.

39
Q

Where is pulmonary surfactant secreted from within the alveoli?

A

Secreted by type II pneumocytes

40
Q

What other role does pulmonary surfactant have within the alveoli apart from reducing surface tension?

A

It acts to equalise pressure and volume across different alveoli.

41
Q

How does pulmonary surfactant act to equalise pressure and volume across different alveoli?

A

It does this because as the alveoli expand, the concentration of pulmonary surfactant molecules decreases, increasing surface tension. This causes the larger alveoli to collapse into smaller ones, helping consistent inflation of the lungs.

42
Q

How does pulmonary surfactant help to prevent pulmonary oedema?

A

Surface tension produced at the air-liquid interface increases hydrostatic pressure increasing filtration (fluid is pulled out of surrounding capillaries and into the alveoli).

By reducing surface tension, pulmonary surfactant helps to prevent alveolar oedema as it means a reduction in hydrostatic pressure and so less fluid entering alveoli from capillaries.

43
Q

What can occur as a result of low levels of pulmonary surfactant within the alveoli?

A

Stiff (low compliance) lungs, alveolar collapse, oedema

Physiology 1 (31 decks)

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