Ventilation and Mechanics of the Lungs (S2)

Question 1

What is the Resting Expiratory Level?

Answer 1

The equilibrium position when the inward force of the elastic recoil of the lungs is balanced by the outward recoil of the chest wall. This corresponds to the state of the lungs as the end of normal quiet expiration.

Question 2

What does the pleural seal ensure?

Answer 2

Holds the outer surface of the lungs to the inner surface of the chest wall. This seal ensures that the chest wall and lungs move together.

Question 3

What is the functional residual capacity?

Answer 3

The lung volume that still exists at the end of expiration, at resting expiratory level.
At FRC the elastic forces of the lung and chest wall are balanced.

Question 4

What muscles are involved in breathing in from the equilibrium position?

Answer 4

Contraction of the diaphragm and the external intercostal muscles

Question 5

What muscles are involved in breathing out during quiet expiration?

Answer 5

None, passive recoil of the lungs

Question 6

What muscles are involved in breathing out during forced expiration?

Answer 6

Contraction of the abdominal muscles and the internal/inner intercostal muscles

Question 7

Describe the steps to breathing in and out?

Answer 7

Inspiratory muscles contract –> thoracic cavity expands –> pleural pressure becomes more negative (increase in Vol) –>transpulmonary pressure increases –> lungs inflate –> alveolar pressure becomes sub-atmospheric –> air flows into the lungs until alveolar pressure= atmospheric pressure

Question 8

What is Boyle’s Law?

Answer 8

pressure of gas is inversely proportional to its volume

Question 9

Describe the process involved which leads to the expiration of air out of the lungs (involving Boyle’s Law)

Answer 9

in quiet expiration, when muscle contraction ceases, the elastic recoil of the lung, results in a decrease in volume of the thorax and lung. The decrease in volume leads to and increase in pressure in the terminal and respiratory bronchioles to above atmospheric pressure so air flows back out again.

Question 10

How far does fresh atmospheric air reach and what does this maintain?

Answer 10

Only reaches as far as the terminal and respiratory bronchioles. Exchange of O2 and CO2 occurs by diffusion between atmospheric air in the terminal and respiratory bronchioles and alveolar gas. Maintaining the composition of alveolar gas

Question 11

What is the pressure within the pleural cavity and why?

Answer 11

Slightly less than atomospheric pressure, because the lungs and chest wall recoil in opposing directions

Question 12

Describe the pleural pressure during the respiratory cycle

Answer 12

In quiet expiration the pressure in the pleural cavity remains negative relative to atmospheric pressure, through out the respiratory cycle. In inspiration, as the chest wall expands outwards, the pleural pressure becomes more negative and returns to the original negative pressure as the lungs retunrs to the resting expiratory level.

Question 13

Describe the affect of diaphragm and ex. IC muscle contraction

Answer 13

The diaphragm moves down to increase the vertical dimensions and the External intercostal muscles move in a ‘bucket handle movement’ to increase the antero-posterior and transverse diameters of the thorax

Question 14

What muscles are used in force inspiration?

Answer 14

The sternocleidomastoid and scalene muscles of the neck and the serratus anterior and pectoralis major muscles

Question 15

What forces does the diaphragm have to go against during inspiration?

Answer 15

Stretching of the elastic tissue of the lung and the stretch the film of fluid lining the alveoli (surfactant)

Question 16

What is compliance?

Answer 16

The volume change per unit pressure change

The stretchiness of the lungs

Question 17

In terms of stetch, what does higher compliance mean?

Answer 17

The higher the compliance the easier it is to stretch

Question 18

What two properties determine the elasticity of the lungs?

Answer 18

Elastic tissue in the lungs (primarily elastin fibres)
and
The surface tension forces of the fluid lining the alveoli

Question 19

What cells produce surfactant?

Describe the constituents or surfactant

Answer 19

Type II pneumocytes (10%)
90% phopholipids 10% protein
important protein = protein A

Question 20

What is the orientation of the phospholipids in the surfactant?

Answer 20

The hydrophillic ends of the molecules lie in the alveolar fluid and the hydrophobic ends project into the alveolar gas

Question 21

How does surfactant reduce surface tension?

Answer 21

The phospholipids float on the surface of the lining fluid, interspersed between fluid molecules disrupting the interaction between the surface molecules thereby reducing tension
Essentially breaks up H-bonds

Question 22

How does surface tension alter the ability to stretch the lung?

Answer 22

the higher the surface tension the harder it is to stretch the lungs
need to exceed elastic recoil

Question 23

Describe the changes in surface tension as the alveoli expand?

Answer 23

as the alveolus expands its surface area increases and the surfactant molecules are spread further apart, making them less efficient in reducing surface tension.
As the alveolus expands the surface tension of the fluid increases

Question 24

Why is the force required to expand small alveoli less than that required to expand large ones?

Answer 24

The surfactant molecules are closer together, therefore more efficient in smaller alveoli.

Question 25

How do the properties of surfactant serve to stabilse the lungs (bubbles)?

Answer 25

Prevents small alveoli collapsing into big ones.
Alveoli vary in size, if the surface tension was constant the alveoli would collapse to form few huge air spaces. this would drastically reduce SA available for GE.
As the alveolus expands increasing its radius, the surfactant molecules are spread out therefore increasing surface tension.
Pressure = 2X surface tension/ Radius
As alveoli increase: T and R both increase
As alveoli shrinks: T and R both decrease
Pressure within small and large alveoli are the same, this stabilises the lung and prevents small alveoli collapsing into big ones.

Question 26

What are the 3 functions of surfactant?

Answer 26

1. increases lung compliance by reducing surface tension
2. Stabilises the lungs, by preventing small alveoli collapsing into big ones
3. Prevents the surface tension in alveoli creating a suction force tending to cause transduction fluid from pulmonary capillaries

Question 27

What is respiratory distress syndrome of the newborn?

symptoms and treatment

Answer 27

Lung surfactant is absent from alveoli of a fetus younger than 25 weeks. RDs syndrome usually seen in those less than 30 weeks
symptoms: cyanosis, grunting, intercostal and subcostal recession
Treatment: surfactant replacement via endotracheal tube and supportive treatment with oxygen and assisted ventilation

Question 28

What is the Law of Laplace?

Answer 28

Pressure= 2 X surface tension/ radius

bubbles

Question 29

Why does most of the resisance to breathing in the URT?

except when the small airways are compressed in forced expiration

Answer 29

Poiseulle’s Law (when flow is laminar): resistance increases with decreasing radius. however the combined resistance of the small airways is normally low because they are connected in parallel over a branching structure.

Question 30

What is asthma caused by?

Answer 30

Inflammatory mediators released as result of hypersensitivity reactions causing contraction of the bronchial smooth muscles and inflammatory swelling of the mucosa leading to narrowing of the small airways

Question 31

what are the airways narrowed by in COPD?

Answer 31

The host response to inhaled cigarette smoke and other toxins causes chronic inflammation and oxidative injury. the airways are narrowed by:

1. Excessive mucous in the lumen (the combined result of increased mucous production and reduced mucus clearing due to ciliary dysfunction)
2. Breakdown of elastin leading to destruction of alevolar walls which cause a loss of ‘radial traction’ - the outward tugging action for the alveolar walls on the small bronchioles- which hold them open.

Question 32

At rest how much oxygen does breathing consume (energy used)?

Answer 32

0.1%