Ventilation And Lung Mechanics

Question 1

What is Venilation?

Answer 1

The process of inspiration and expiration

Question 2

What neurons are responsible for normal involuntary breathing? How?

Answer 2

Neurons in respiratory centres of brain generate automatic rhythmic impulses, which travel via spinal cord and peripheral nerves to the inspiratory muscles

Question 3

What is the Tidal Volume?

How much in most people?

Answer 3

Volume of air which enters and leaves lungs with each breath

400-500ml

Question 4

What is the IRV? (Inspiratory Reserve Volume)

Answer 4

Additional amount of air that can be inhaled after a normal inhalation

Question 5

What is the ERV? (Expiratory Reserve Volume)

Answer 5

Additional amount of air that can be exhaled after a normal exhalation

Question 6

What is the Residual Volume?

Answer 6

The amount of air left in lungs, even after a forced expiration (cannot be breathed out)

Question 7

Lung capacities are defined relative to 3 points in the breathing cycle;

• Maximum inspiration
• Maximum expiration
• End of quiet expiration

What is the Inspiratory Capacity?

Answer 7

• From end of quiet expiration to maximum volume

IRV + Tidal Volume

Question 8

Lung capacities are defined relative to 3 points in the breathing cycle;

• Maximum inspiration
• Maximum expiration
• End of quiet expiration

What is the Functional Residual Capacity?

Answer 8

• Volume of air in lungs at end of quiet expiration

ERV + RV

Question 9

Lung capacities are defined relative to 3 points in the breathing cycle;

• Maximum inspiration
• Maximum expiration
• End of quiet expiration

What is the Vital Capacity?

Answer 9

• Inspiratory capacity (TV + IRV) + ERV

Amount of air you can forcefully breath in and expire
(Returns you to Residual Volume)

Question 10

What is the total lung capacity?

Answer 10

Vital capacity + Residual Volume

Question 11

Only part of the Tidal Volume is available for gas exchange, the rest fills the anatomical dead space

What is the Anatomical Dead Space?

Answer 11

The volume of the conducting airways that does not take part in gas exchange

Question 12

What is the Alveolar Dead Space?

Answer 12

The alveoli that do not take part in gas exchange (may be due to damage/ lack of perfusion)

Question 13

What is Physiological Dead Space?

Answer 13

Anatomical Dead Space + Alveolar Dead Space

Question 14

How do you calculate Tidal Volume using anatomical dead space and air in alveoli?

Answer 14

Air in alveoli + air in anatomical dead space

Question 15

How do you calculate total pulmonary ventilation/ minute volume?

Answer 15

Tidal Volume * Respiratory rate

Question 16

How do you calculate alveolar ventilation?

Answer 16

(TV- Dead Space)* respiratory rate

Question 17

Of Inspiration and Expiration, which is passive and active?

Answer 17

Inspiration- Active (Muscles contact)

Expiration- Passive (Muscles relax, lung’s elastic recoil returns thoracic cavity to original position)

Question 18

At rest, at the end of quiet expiration describe the 2 forces acting on the lungs

What is the net effect?

Answer 18

• Inward: Lung’s elasticity and surface tension generate an inwardly directed force
• Outward: Elasticity of rib cage’s muscles and connective tissues generate in outwardly directed force
• Balance each other out, creating a negative pressure within Intrapleural space (visceral pleura pulled inwards and parietal pulled outwards)

Question 19

How much pleural fluid is there normally?

Answer 19

10ml

Question 20

Briefly describe the intrapleural pressure changes During the breathing cycle

Answer 20

• Negative pressure at rest
• Becomes more negative during inspiration
• Returns to resting negative pressure at end of quiet expiration

Question 21

What are 2 sources of the Elastic Recoil of the lungs?

Answer 21

• Elastic tissue in lungs

- Surface tension forces of fluid lining alveoli?

Question 22

What if the pleural seal was broken?

Answer 22

During expansion of rib cage, lungs would not expand but would collapse inwards on themselves

Question 23

In forced inspiration (exercise/ disease affecting lungs), accessory muscles are used

Name the 4 of them

Answer 23

• SCM
• Scalene muscles
• Serratus Anterior
• Pec Major

Question 24

Name 2 groups of Accessory muscles used in Forced Expiration

Answer 24

• Internal Intercostal muscles

- Abdominal Wall Muscles (RA, EO and IO)

Question 25

What are 2 ways energy is expended during breathing

Answer 25

- To stretch the lungs | - To overcome airway resistance

Question 26

What is the Compliance of the lungs? How is it defined?

Answer 26

- Distensibility (stretchiness) of the lungs Volume change per pressure change

Question 27

Describe the effect of the film of fluid lining the alveoli

Answer 27

- The fluid’s Surface Tension opposes any increases in alveolar surface area (Decreased compliance makes it difficult for alveoli and therefore lungs to expand)

Question 28

Describe the substance we use to counter the Surface Tension of the fluid lining the alveoli? Why do they float on the surface of the lining fluid? (It has detergent properties)

Answer 28

- Surfactant (mix of phospholipids and proteins) secreted by Type II Pneumocytes - Hydrophilic ends lie in alveolar fluid, Hydrophobic ends project into alveolar gas

Question 29

How does Surfactant act to reduce the effect of the fluid lining the alveoli?

Answer 29

- Interspersed between fluid molecules - Distrupting interaction between them - Thus reducing surface tension

Question 30

Explain why less force is needed to expand smaller alveoli

Answer 30

- In larger alveoli, surfactant molecules are further apart so are less efficient, so surface tension is greater - In smaller ones, surfactant molecules are closer so more efficient, so surface tension is weaker (Also applies to when alveoli expand)

Question 31

Alveoli are basically a series of interconnected bubbles, the pressure of which is determined by the Law of Laplace. LoL: Pressure =2T/r (T is Surface tension, r is radius) What 3 things would happen if T was constant in all alveoli?

Answer 31

- Smaller alveoli would have higher pressures so would empty into large alveoli with lower pressures - Thus, smaller alveoli would collapse into larger ones to form a few huge air filled spaces (Bullae) - This significantly reduces surface area for gas exchange

Question 32

How does Surfactant prevent Bullae forming and reducing SA for gas exchange?

Answer 32

- As alveolus expands, surfactant is less effective, so Surface Tension increases, increasing pressure inside it - Therefore different sized alveoli can have same pressure preventing Bullae formation (Pressure= 2T/r)

Question 33

Other than Increasing Lung compliance and Preventing small alveoli collapse into larger ones, what 3rd thing does surfactant do?

Answer 33

Prevents surface tension in alveoli creating a suction force which can cause transudation of fluid from pulmonary capillaries into alveoli

Question 34

Why is the resistance of the small airway tubes low? Which part of the RT has the most resistance to breathing (At rest work of breathing only consumes 0.1% of total O2 consumption)

Answer 34

Connected in parallel hence very large effective diameter Therefore most of resistance to breathing is in Upper RT

Question 35

How are Elastance and Compliance related?

Answer 35

Inversely proportional

Question 36

Diameter is the main factor affecting airway resistance What are 3 things that affect the diameter?

Answer 36

- Mucus in airways - Pulmonary pressure gradients (High intrapulmonary pressures increase diameter) - Radial Traction

Question 37

What is Radial Traction? How is it affected in expiration?

Answer 37

Outward pulling on bronchiole from Alveolar walls (Prevents bronchiole collapse) In expiration, alveolar walls are less effective (due to low alveolar pressure) at keeping bronchioles open so their diameter reduces to an extent

Question 38

Why is there increased airway resistance in expiration

Answer 38

Increased intrapulmonary pressure compresses airways, decreasing their diameter