Ventilation: Physics of Breathing

Question 1

What are the non-respiratory functions of ventilation?

Answer 1

• expulsion of foreign bodies

- defence against infection/disease

Question 2

What is alveolar ventilation

Answer 2

the rate at which new air reaches the areas of gas exchange

Question 3

What is dead space air?

Answer 3

• air that is breathed in but never reaches gas exchange areas
• fills respiratory passages
• nose
• pharynx
• trachea

Question 4

What are the ways that the lungs can be expanded and contracted?

Answer 4

• downward and upward movement of the diaphragm to lengthen/shorten chest cavity (quiet breathing)
• elevation and depression of the ribs to increase/decrease anteroposterior diameter of chest cavity

Question 5

What are the important muscles that raise the rib cage?

Answer 5

• external intercostals
• sternocleidomastoid (life sternum upwards)
• anterior serrati (lift many ribs)
• scaleni (lift first 2 ribs)

Question 6

What are the important muscles that lower the rib cage?

Answer 6

• abdominal recti

- internal intercostals

Question 7

What creates the suction effect in the lungs?

Answer 7

• lymph drainage of excess fluid between the lung pleural membrane and pleural surface of thoracic wall
• lungs held against the thoracic wall

Question 8

What is intrapleural pressure?

Answer 8

• pressure of fluid in the thin space between lung pleura and chest wall pleura
• usually slightly negative pressure
• varies over length of lungs

Question 9

Explain how intrapleural pressure changes during respiration

Answer 9

• inspiration: expansion of chest cage pulls lungs outward
• negative pressure increases to about -7.5cm H2O
• air sucked into lungs
• expiration is opposite

Question 10

What is alveolar pressure?

Answer 10

pressure of air inside lung alveoli

Question 11

Explain how alveolar pressure changes during respiration?

Answer 11

• when glottis is open and no air flowing, pressure in all parts of respiratory tree is equal to atmospheric pressure
• inspiration: chest wall expansion, alveolar pressure decreases to about -1cm H2O
• pulls 0.5L into lungs
• expiration: opposite occurs

Question 12

What is transpulmonary pressure?

Answer 12

• pressure difference between that in the alveoli and that on the outer surfaces of the lungs
• measure of elastic forces that tend to collapse lungs

Question 13

What processes in respiration is energy needed for?

Answer 13

• contracting muscles for inspiration (in quiet breathing diaphragm comprises 75% of energy expenditure)
• stretch elastic elements
• overcome airway resistance
• overcome frictional forces arising from viscosity of the lung and chest wall
• overcome intertia of air and tissues

Question 14

What has the greatest effect on airway resistance?

Answer 14

airway radius

Question 15

In what conditions is turbulent flow more likely?

Answer 15

high velocities and large diameter airways

Question 16

What is static compliance?

Answer 16

• the extent to which the lungs will expand for each unit increase in transpulmonary pressure

Determined by :

• elastic forces of lung tissue itself (determined by elastin and collagen fibres among lung parenchyma)
• elastic forces caused by surface tension of fluid that lines alveoli

Question 17

What is the correlation between elastic recoil and compliance?

Answer 17

high compliance means low elastic recoil

Question 18

Describe the composition of lung tissue when inflated/deflated?

Answer 18

• deflated: fibres are contracted and kinked

- inflated: fibres stretched and unkinked

Question 19

Describe the changes to the lung in pulmonary fibrosis

Answer 19

• deposition of fibrous tissue making lung stiff
• lung compliance decreased
• smaller changes in lung volume for small changes in transpulmonary pressure
• patients breathe more shallowly and rapidly
• decreases in RV, FRC and TLC

Question 20

Describe the changes to the lung in emphysema (COPD)

Answer 20

• alveolar and capillary walls progressively destroyed, elastic tissue
• lung compliance increased
• larger changes in lung volume for smaller changes in transpulmonary pressure
• airway resistance increased
• patients breathe more slowly and deeply
• increases in RV, FRC and TLC

Question 21

Describe the lung changes in chronic bronchitis (COPD)

Answer 21

• mucus and airway inflammation produce an increase in airway resistance
• increases in RV, FRC and TLC
• compliance is normal

Question 22

What is surface tension?

Answer 22

measure of the force acting to pull a liquid’s surface molecules together at an air-liquid interface

Question 23

Describe the production of surfactant

Answer 23

• lipid components enter type II cell from bloodstream
• secreted by type II alveolar epithelial cells
• alveolar macrophages help in degrading surfactant
• type II cells take up rest and recycle/destroy it

Question 24

What makes up surfactant mixture?

Answer 24

• DPPC

- proteins: surfactant apoproteins (SP-A/B/C/D)

Question 25

Describe the role of surfactant

Answer 25

• reduces surface tension of H2O minimising fluid accumulation in alveolus
• increases compliance to it is easier to inflate the lungs
• reduces pressure 4.5 times
• helps keep alveolus size relatively uniform during respiratory cycle

Question 26

What is the method for studying pulmonary ventilation?

Answer 26

spirometry

Question 27

What is tidal volume?

Answer 27

volume of air inspired or expired with each normal breath

Question 28

What is inspiratory/expiratory reserve volume?

Answer 28

• inspiratory reserve volume: extra volume of air that can be inspired over and above normal tidal volume
• expiratory reserve volume: max extra volume of air that can be expired by forceful expiration after end of normal tidal expiration

Question 29

What is residual volume?

Answer 29

volume of air remaining in lungs after most forceful expiration