4.4 Mechanisms of Ventilation

Question 1

Respiration involves which two processes?

Answer 1

• Ventilation (mechanical conduction of air; breathing)
• Gas exchange (diffusion)

Question 2

Which muscles are used in respiration?

Answer 2

• Diaphragm
• Intercostal muscles

Question 3

Which bones are involved in respiration?

Answer 3

• Ribs
• Sternum
• Vertebral column

Question 4

What are the two layers of the pleura?

Answer 4

• Visceral (inside; think of Bloodborne)
• Parietal (outside)

Question 5

Which extracellular structures are involved in respiration?

Answer 5

• Elastic fibres

Question 6

Which afferent nerves are involved in respiration?

Answer 6

Sensors and processors in:
- Blood vessels
- Lungs
- Brainstem

Question 7

Which efferent nerves are involved in respiration?

Answer 7

Phrenic (diaphragm) nerves and intercostal nerves

Question 8

What is the border between the upper and lower airways?

Answer 8

The larynx (it talks, after all)

Question 9

Why doesn’t gas exchange occur in our mouths?

Answer 9

Air must be modified before gas exchange

Question 10

What modifications are made to air before gas exchange?

Answer 10

• Humidification
• Warming
• Cleaning

Question 11

What is the anatomical dead space of the respiratory system?

Answer 11

Areas of no gas exchange

Question 12

What is the volume of the respiratory dead space?

Answer 12

150mL

Question 13

What is meant by alveolar dead space?

Answer 13

All alveoli that are not perfused with blood

Question 14

What makes up the physiological dead space of the respiratory system?

Answer 14

Anatomical dead space + alveolar dead space

Question 15

In which structures can gas exchange occur during respiration?

Answer 15

• Respiratory bronchioles
• Alveoli

Question 16

What is meant by compliance?

Answer 16

Distensibility/resistance against stretching; how much volume of air can be added per pressure? (higher, more compliance)

Question 17

What is meant by recoil?

Answer 17

The force that opposes stretching of the lungs

Question 18

What is the relationship between recoil and compliance?

Answer 18

Inversely proportional; the more force acts against stretching, the lower the compliance of the lung.

Question 19

What is the parietal pleura connected to?

Answer 19

The endothoracic fascia

Question 20

What is the relationship between the visceral and parietal pleura?

Answer 20

They are connected: think: fist and balloon.

Question 21

What is the purpose of the liquid between the visceral and parietal pleura?

Answer 21

Adhesion

Question 22

Why is it important that the visceral and parietal pleura are connected?

Answer 22

The visceral pleura is connected to the parietal pluera, which is connected to the endothoracic cavity. Therefore, when the thoracic cavity increases in volume, so too do the lungs.

Question 23

What structures must be able to move in order for the lungs to expand during ventilation? How do they do this?

Answer 23

• Diaphragm (contracts)
• Ribs (bucket handle and pump handle movement)

Question 24

What is Boyle’s Law?

Answer 24

V1 x P1 = V2 x P2 (before and after inspiration)

Question 25

What prevents alveoli from collapsing in on themselves, given that they want to?

Answer 25

Surfactant

Question 26

How is work of breathing calculated?

Answer 26

Work = Pressure x Volume

Question 27

What percentage of work is dedicated to quiet vs resistive work during quiet breathing?

Answer 27

• 65% elastic (expanding during inspiration)
• 35% resistive (overcome airway resistance etc.)

Question 28

Why does airway resistance increase during intubation?

Answer 28

• Intubation increases the length of the airway
• When you increase the length, you also increase the resistance to flow (the same as blood vessels)

Question 29

What two factors influence the simplified calculation of airway resistance?

Answer 29

• Pressure gradient
• Volumetric airflow

IT’S JUST OHM’S LAW (Poiseuille’s law also works)

Question 30

Why does it make sense that people with asthma have increased resistance to breathing?

Answer 30

As airways become inflamed, they reduce in radius. Since resistance is proportional to the fourth power of the radius, this can result in a radical increase in airway resistance.

Question 31

What are the four components of respiration?

Answer 31

• Ventilation
• Diffusion
• Gas Transport
• Gas Exchange

Question 32

Summarise Boyle’s Law in words

Answer 32

Pressure of gas is inversely proportional to its volume

Question 33

What mechanisms are involved in quiet inspiration and expiration?

Answer 33

INS: Diaphragm flattens, lungs lengthen
EXP: Diaphragm relaxes, elastic recoil of lungs and chest wall

Question 34

What additional mechanisms are involved in forced/effortful breathing?

Answer 34

INS: Intercostal muscles (mostly external) act to to raise rib cage
EXP: Abdominal recti and (mostly) internal intercostals

Question 35

What is transpulmonary pressure?

Answer 35

The gap between alveolar pressure and pleural pressure

Question 36

Recall the equation for compliance

Answer 36

C = deltaV/deltaP

Question 37

How does surface tension influence the collapse of alveoli?

Answer 37

The particles in the wall of the alveoli are attracted to one another, and so the lungs constantly want to collapse on themselves

Question 38

Recall the law of LaPlace

Answer 38

Pressure = 2T/r

T: Surface tension
r: Radius

Question 39

What air modification occurs during expiration?

Answer 39

1. Air is cooled, returning some of the heat into the upper airways
2. Some water is reclaimed through condensation

Question 40

What is the opposite of turbulent?

Answer 40

Laminar