Lecture 1 - Lung Mechanics + Ventilation

Question 1

What 2 portions is the respiratory tract split into?

Answer 1

1) Conducting Portion - the anatomical dead space, conducts air to the alveoli and bronchioles.
2) Respiratory Portion - involving the bronchioles and alveolus where gas exchange occurs.

Question 2

What is the difference between ventilation and respiration?

Answer 2

• Ventilation is the movement of gas into and out of the lungs.
• Respiration is exchange of O2 + CO2 across a membrane either in the lungs or at the cellular level.
• Ventilation must occur for respiration to occur.

Question 3

Define “tidal volume”

By what principle does air move in and out of the body?

Answer 3

• Volume of air being moved during ‘quiet’ inspiration and expiration.
• Gas moves from greater to lower pressure areas so air moves into the lungs by changing lung pressure.

Question 4

What is Boyle’s Law?

How does Boyle’s Law allow quiet inspiration and expiration to occur? (describe the processes)

Answer 4

• Inverse relationship between pressure of gas and the volume it occupies.
• Inspiration = expansion of thoracic cavity & lungs, increases volume which decreases intrapulmonary (in the lungs) pressure, atmospheric air moves in.
• Expiration = air expelled passively by relaxing muscles used in inspiration, reduced thoracic cavity volume, increased intrapulmonary pressure, air moves to atmosphere.

Question 5

The pleura connect the lungs to the chest wall, what are the 3 components of the pleura?
How does the pleura allow the lung to move with the chest wall?

Answer 5

Pleura is a pair of serious membranes:

1) Parietal Pleura = lines inside of each hemi-thorax
2) Visceral Pleura = lines outside of each lung
3) Intrapleural space = potential space between the two pleuras containing about 15mL of fluid

Pleural fluid creates surface tension, allows lung to move with chest wall

Question 6

What factor in the lungs keeps alveoli/lungs from fully collapsing with each expiration?

Answer 6

• Lungs have natural inward elastic recoil, chest wall has natural outward recoil.
• Two opposing forces creates negative intrapleural pressure, which stays negative throughout respiration
• Pressure is negative so prevents alveoli/lungs from fully collapsing in expiration

Question 7

What is transpulmonary pressure?

Answer 7

The difference between intrapulmonary and intrapleural pressure.

Question 8

Define compliance and elastance
How are these properties related?
How is compliance related to alveolar fluid tension?

Answer 8

• Compliance is a measure of distensibility, i.e.: how well the lungs will expand
• Elastance is a measure of elastic recoil, how well the lungs will return to its original size.
• The two are inversely proportional, in tissues with high compliance, the elastic recoil is less (and vice versa)
• Inversely proportional, surface tension too high = compliance decreased

Question 9

What 2 things are lung elastic recoil directly related to?

What 1 thing is lung elastic recoil inversely related to\?

Answer 9

1) Connective tissue surrounding alveoli - containing elastin and collagen.
2) Alveolar fluid surface tenions

1) Lung compliance

Question 10

What is the resting expiratory level & why does this occur?

What is the volume of air at REL also known as?

Answer 10

• When we have just expired just before inspiring again. Equal elastic recoil force between lungs (inwards) and chest wall (outwards) so there is no net movement of chest wall.
• Functional Residual Capacity (FRC)

Question 11

What would happen to the position of resting expiratory level when the elastic recoil is weaker and when the elastic recoil is stronger in pathological states? & what would happen to FRC?

Answer 11

• If recoil is weaker, chest wall would be further away from lungs, therefore FRC would increase.
• If recoil is stronger, chest wall would be closer to lungs, therefore FRC would decrease.

Question 12

What is the effect of surface tension created by fluid on alveoli on compliance and elastance?
What product of type ll pneumocytes counteracts surface tension & how?

Answer 12

• Surface tension limits expansion of alveoli, decreasing compliance and increasing recoil.
• Surfactant, disrupts interaction between fluid molecules on alveolus surface via detergent properties.

Question 13

Is surfactant more or less effective on larger alveoli compared to smaller & why?

Answer 13

• Less effective, surfactant molecules are further apart, xo less effective at disrupting surface tension. Surface tension therefore increases as the alveoli size increases.
• Smaller alveoli = more surfactant per surface area = less surface tension = better compliance.

Question 14

Ventilation needs to overcome airways resistance to flow. What 2 things does this resistance depend on & which one is more important?

Answer 14

1) Surface tension

2) Airway diameter - most important (Poiseuille’s Law)

Question 15

Forced inspiration and expiration require more effect and recruit more muscles, what are these accessory muscles recruited for each?

When are these muscles used?

Answer 15

Expiration accessories = SCM, scalene muscles, serratus anterior & pec major

Inspiration accessories = internal intercostals + abdominal wall muscles.

• In exercise and in diseases affecting the lung.

Question 16

Define:

1) Inspiratory reserve volume (IRV)
2) Expiratory reserve volume (ERV)
3) Tidal volume
4) Functional residual capacity (FRC)

And give their normal values.

Answer 16

1) Amount of air that can be forcibly inhaled after tidal volume (1900-3300mL)
2) Amount of air that can be forcibly exhaled after tidal volume (800-1200mL)
3) Amount of air moving in and out of lungs during 1 respiratory cycle (350-500mL)
4) Volume remaining in the lungs after passive expiration (3000mL)