Ventilation and Mechanics

Question 1

Define tidal breathing

Answer 1

Inhalation and exhalation during restful breathing

Question 2

How do we breath in?

Answer 2

Active

Diaphragm contract = down

Rib cage expands by external intercostal muscles

Pressure falls below atmospheric pressure = air inflow until equal pressure

Question 3

How do we breath out?

Answer 3

Passive

Muscle contraction ceases, muscles relax

Elastic recoil = return to resting end-expiratory level = exhalation

Question 4

Define inspiratory reserve volume (IRV)

Answer 4

Amount you can breathe in over you tidal volume

Maximal amount of additional air that can be drawn into the lungs by determined effort after normal inspiration

Question 5

Define tidal volume (TV)

Answer 5

Amount of air entering the ling during a normal inhalation at rest

Question 6

Define expiratory reserve volume (ERV)

Answer 6

Maximal volume of air that can be expelled from the lungs after normal expiration

Question 7

Define residual volume (RV)

Answer 7

Volume of air still remaining in the lungs after the most forcible expiration possible

Question 8

Define total lung capacity (TLC)

Answer 8

Volume of air contained in the lungs at the end of maximal inspiration

Question 9

Define vital capacity (VC)

Answer 9

Volume of air that can be expelled from the lungs after taking the deepest possible breath

Question 10

Define inspiratory capacity (IC)

Answer 10

Total amount of air that can be drawn into the lungs after normal expiration

Question 11

Define functional residual Capacity (FRC)

Answer 11

Volume of air remaining in the at the end of a passive expiration

Determined by = balance of elastic forces of the chest wall, favouring outward expansion, and the elasticity and surface tension of the lung, favouring a smaller lung vol

Question 12

Explain what is meant by the resting end-expiratory level

Answer 12

volume at which the elastic forces acting to make the rib cage spring out are balanced by the elastic recoil of the lung

Question 13

At end-expiration what is the pressure in the pleural space?

Answer 13

Slightly -ve

Due to pull outward by chest wanting to expand and lungs pulling inward wanting to collapse

Question 14

What are the accessory muscles of inspiration and expiration

Answer 14

Inspiration = SCM, scalene, pect major/minor/trapz

Expiration = internal intercostals, muscles of abdo wall

Question 15

Explain the importance of the pleural seal in respiration

Answer 15

~10ml pleural fluid

Seal the lungs to the chest wall

At end-expiration pleural space pressure is slightly -ve

Question 16

What happens when the pleural seal is broken?

Answer 16

Lung can collapse

Question 17

Outline the pleural pressure changes during respiratory cycle

Answer 17

Inhalation = pressure falls

Exhalation = pressure raises

Question 18

Explain how a pneumothorax occurs and why this results in collapse of the lung

Answer 18

Broken pleural seal

Air fills the pleural cavity

-ve pressure lost

Lung able to collapse

Question 19

Define the term ‘compliance’ of the lungs

Answer 19

Measure of the lungs ability to stretch and expand

C = Δvolume/Δpressure

Stiff = low compliance (fibrosis)

Slack = high compliance (emphysema)

Question 20

Describe the factors which affect the compliance of the lungs

Answer 20

age = lungs less elastic

Fibrosis = stiffer

Surface tension

Question 21

Explain the effect of surface tension in the alveoli

Answer 21

Water surface tension wants to collapse the alveoli

Question 22

Outline the role of surfactant

Answer 22

acts to reduce surface tension by breaking up H-bonds

Preventing the collapse of alveoli

Question 23

What is surfactant and when is produced?

Answer 23

Mixture of lipids and proteins

Secreted by alveolar cells

Prod begins 25-28

Adequate levels at about 35 weeks GA

Question 24

What is the net effect of surfactant in a small bubble vs a big one?

Answer 24

Surfactant spread more thinly as bubble expands, so surfactant is less effective and surface tension increases in the bigger bubble

= same in bigger and smaller bubble so overall structure remains the same

Question 25

Explain the altered lung-mechanics in respiratory distress of the newborn

Answer 25

Reduced surfactant levels

Higher risk of alveoli collapse = reduced ventilation

Question 26

How does lung fibrosis affect lung-mechanics?

Answer 26

stiff lung = smaller vol

Require a bigger pressure change to change the volume

Question 27

How does emphysema change the normal lung-mechanics?

Answer 27

Increased amounts of elastase = destruction of elastin and breakdown of alveolar walls = larger airspaces

Lung compliance increased = slack lung

Question 28

Explain how asthma affects lung-mechanics

Answer 28

Sustained breathing at high lung volume is known to cause stress relaxation of the lung

Slack lung = increased compliance

Question 29

Describe how COPD changes lung-mechanics

Answer 29

Increase in pulmonary compliance due to the loss of alveolar and elastic tissue

Air sacs no longer bounce back to their original shape

Airways can also become swollen or thicker than normal, and mucus production might increase

The floppy airways are blocked, or obstructed, making it even harder to get air out of the lungs

Question 30

How does a pneumothorax change normal lung-mechanics?

Answer 30

Lower lung compliance as lung cant inflate against air in the pleural cavity

Question 31

What is minute ventilation?

Answer 31

Volume inhaled/exhaled from the lungs per minute

Resp frequency x tidal vol = L/min

Question 32

Define anatomical (serial) dead space

Answer 32

Upper resp tract between mouth and resp bronchioles, about 150ml in adults

Question 33

Define alveolar (distributive) dead space

Answer 33

Where alveoli are ventilated but not perfused, or very poorly perfused

Question 34

Define physiological dead space

Answer 34

Combination of alveolar and anatomic dead space

Question 35

At what division in the bronchial tree do we move from the conducting zone to the respiratory zone?

Answer 35

After 14-15 divisions

Question 36

Where in the bronchial tree is the main site of airway resistance?

Answer 36

Upper respiratory tract due to turbulent air flow

Question 37

Outline the different mechanisms of increased airway resistance

Answer 37

Increased mucus

Hypertrophy of the smooth muscle and/or oedema

Loss of radial traction = lung not able to hold the airway open

Question 38

How is resistance of the airway calculated?

Answer 38

Res = pressure / flow

Question 39

How is airway function assessed?

Answer 39

spirometry