L15 Respiratory Physiology

Question 1

What are the physical; factors that influence pulmonary ventilation?

Answer 1

1) airway resistance - anything that impedes air flow through the respiratory tract
2)alveolar surface tension - alveoli are covered with a thin film of liquid composed mainly of water creating a gas-water boundary
3)lung compliance - the ability of the lungs and chest walls to stretch

Question 2

What is airway resistance?

Answer 2

• the opposition of flow caused by the forces of friction
• the ratio of driving pressure to the rate of air flow

Question 3

What is airway resistance determined by?

Answer 3

• length of system (constant)
• airway diameter -> wider airways have less resistance
• flow : laminar (low R) or turbulent (high R)
• viscosity of gas (usually constant)

Question 4

What is the equation for flow rate?

Answer 4

Driving pressure / r to the power of 4

Question 5

What factors affect gas exchange in the alveoli?

Answer 5

1) oxygen reaching the alveoli
2) gas diffusion between alveoli and the blood
3) adequate perfusion of alveoli

Question 6

Why do bronchi have the highest resistance?

Question 7

Under what conditions does resistance increase?

Answer 7

• Inflammation of airways
• Increased mucus secretion
• Presence of a tumour

Question 8

What is bronchodilation?

Answer 8

Airway resistance decreases as smooth muscle relaxes
-> increase in diameter of airway

Question 9

What is bronchoconstriction?

Answer 9

Airway resistance increases as smooth muscle contracts
-> decrease in diameter of airway

Question 10

What is central control in the bronchioles?

Answer 10

The parasympathetic innervation of airways
- bronchoconstriction increases resistance
There is NO sympathetic innervation of airways

Question 11

What is non-neural control in bronchioles?

Answer 11

Sympathetic beta2 receptors present on smooth muscled activated by circulating adrenergic agonists (adrenaline)
- bronchodilation decreases resistance

Question 12

How is surface tension formed in alveoli?

Answer 12

Alveoli are covered with a thin film of liquid (mainly water) which creates a gas-boundary
- Water molecules form hydrogen bonds
- Gases are nonpolar molecules and therefore do not form hydrogen bonds
This creates surface tension at the boundary

Question 13

When is the surface tension in alveoli the greatest?

Answer 13

When the alveoli are at their smallest diameter - during expiration

Question 14

When are alveoli hard to inflate?

Answer 14

When the surface tension is high therefore when alveoli are small

Question 15

What is the role of a surfactant?

Answer 15

Reduces surface tension

Question 16

How is the pressure equalized between small and large alveoli?

Answer 16

Small alveoli have more surfactant than large alveoli
- the more surfactant decreases the surface tension

Question 17

What happens to alveoli with surfactant?

Answer 17

The hydrogen bonds are disrupted and the alveolus remains inflated

Question 18

What happens to alveoli without surfactant?

Answer 18

Hydrogen bonds pull the water molecules together and the alveolus collapses

Question 19

Why can alveoli collapse during expiration?

Answer 19

There is a high amount of unopposed surface tension = atelectasis

Question 20

Why does the surfactant decrease the work of breathing?

Answer 20

• produced by type II alveolar cells
• mixture containing proteins and phospholipids
• similar chemical structure to detergent, with both polar and nonpolar end
• distrusts cohesive force of hydrogen bonding of water
• allows alveolus to remain partially open even during expiration
• more concentration in smaller alveoli therefore increased stability

Question 21

Why does infant respiratory distress syndrome occur?

Answer 21

Surfactant is not produced significantly until the last 10-12 weeks of gestation so premature newborns may suffer

Question 22

What is lung compliance?

Answer 22

The ability of lungs and the chest wall to stretch/distend
The ability of tissue to return to its original state when stretched

Question 23

What is compliance defined as?

Answer 23

The change in volume produced by a change in pressure

Question 24

What is lung compliance affected by?

Answer 24

• Alveolar surface tension : surfactant increases compliance
• Distensibility of elastic tissue of lung : during inflation
• Ability of the chest wall to move or stretch during inspiration

Question 25

What is the tidal volume, TV?

Answer 25

The volume inspired or expired with each normal breath = 500ml

Question 26

What is expiratory Reserve Volume, ERV?

Answer 26

The maximal volume that can be expired after the expiration of a tidal volume/normal breath = 1200ml

Question 27

What is the inspiratory reserve volume, IRV?

Answer 27

The maximum volume that can be inspired over the inspiration of a tidal volume/normal breath = 3100ml
Used during exercise

Question 28

What is residual volume, RV?

Answer 28

The volume that remains in the lungs after a maximal expiration = 1200ml

Question 29

How can pulmonary volumes be measured?

Answer 29

they can be measured using spirometry apart from RV which needs a whole body plethysmography to be measured

Question 30

What is the inspiratory capacity?

Answer 30

The volume of maximal inspiration
TV + IRV = 3600ml

Question 31

What is functional residual capacity, FRC?

Answer 31

The volume of gas remaining in lung after normal expiration
ERV + EV = 2400ml
Cannot be measured by spirometry because it includes RV

Question 32

What is vital capacity?

Answer 32

The volume of maximal inspiration and expiration

Question 33

What is total lung capacity?

Answer 33

The volume of the lung after maximal inspiration

Question 34

What is forced vital capacity, FVC?

Answer 34

A test to assess respiratory function
- Maximum inspiration followed by maximum expiration as fast as possible
- Measure volume of air expired and time
- Normal FEV1/FVC = 80%

Question 35

What is FEV1?

Answer 35

The forced expiratory volume in 1 second

Question 36

Why does restrictive lung disease occur?

Answer 36

FVC is reduced
FEV1 is close to normal

Question 37

Why does obstructive lung disease occur?

Answer 37

FVC is close to normal
FEV1 is reduced

Question 38

What is dead space?

Answer 38

When the conducting airways are ventilated but do not contribute to gas exchange

Question 39

Equation for total pulmonary ventilation?

Answer 39

Ventilation rate X tidal volume

Question 40

Why is TPV greater than alveolar ventilation?

Answer 40

Dead space

Question 41

Equation for alveolar ventilation?

Answer 41

Ventilation rate X Vt - dead space volume

Question 42

What does alveolar ventilation indicate?

Answer 42

How much fresh air reaches the alveoli