Session 2 - Ventilation & Lung Mechanics

Question 1

What are normal blood gas values?

Answer 1

pO2= 9.3-13.3 kPa

pCO2= 4.7-6 kPa

Question 2

What is parenchyma?

Answer 2

The functional tissue of an organ (to distinguish between connective tissue etc)

Question 3

What is the functional residual capacity?

Answer 3

The volume of air left in the lungs at the end of a passive exhalation.

Question 4

Which factors determine the value of functional residual capacity?

Answer 4

The balance of elastic outward, expansive forces of the chest wall, against the elasticity and surface tension of the lung (Favouring smaller lung volume)

Question 5

What is a pneumothorax?

Answer 5

Air in the pleural cavity causing a collapsed lung.

Question 6

Why can a lung not properly expand in a pneumothorax?

Answer 6

The high pressure in the pleural space means the lung cannot expand against this increased force.

Question 7

What is the function of a spirometer?

Answer 7

Measures the total volume of air that can be exhaled or inhaled, and the rate at which a certain volume if expelled from the lungs.

Question 8

Name the accessory muscles of inspiration.

Answer 8

Sternocleidomastoid
Scalene
Pectoral is major & minor
Trapezius

Question 9

What is compliance of the lung?

Answer 9

Compliance is the relationship between pressure and volume.

C= change in volume / change in pressure.

e.g. higher compliance = small change in pressure giving high change in volume (slack lung) like in emphysema.

Question 10

Why do older adults have a higher Functional Residual Capacity (FRC) than young adults?

Answer 10

The lungs are less elastic, meaning the balance between the chest wall and lung tension (inward) has changed (meaning there is a higher FRC)

Question 11

Which condition is commonly seen with low compliance in the lungs?

Answer 11

Fibrosis of lungs

Question 12

How does surface tension affect alveoli of different size?

Answer 12

Surface tension wants to achieve minimum surface area.

Smaller alveoli have > S. tension.
They want to collapse into larger alvoli.

Question 13

How does surfactant affect alveoli?

Answer 13

Surfactant reduces surface tension of alveoli.

Therefore allows easier inflation of lungs (>compliance).
And regulates alveolar size.

Question 14

What is in surfactant?

Answer 14

Complex mixture of lipids secreted by alveolar wall.

Question 15

How does surfactant work?

Answer 15

As alveoli expand, the surfactant molecules spread more thinly over the surface, making it less effective and increasing surface tension in larger alveoli.

Overall ensures the pressure in the large alveoli is the same as in the small, allowing inflation of them all.

Question 16

How is ventilation measured?

Answer 16

Minute ventilation.
In L/min.

Worked out by tidal volume multiplied by breaths per minute.

Question 17

What is dead space?

Answer 17

Volume of air in the lungs which is not available for gas exchange.

Anatomic dead space = Upper Respiratory tract, bronchioles (150ml)

Alveolar dead space = Where alveoli are ventilated but no perfused. (E.g. disease)

Question 18

What is alveolar ventilation?

Answer 18

The volume of air filling the alveoli in Litres per minute.

Question 19

What is the normal amount of anatomical dead space in adults?

Answer 19

About 150ml

Question 20

Why is alveolar ventilation relevant?

Answer 20

Alveolar respiration can be different in two people with the same minute ventilation! (See notes)

Question 21

Where is the main site of airways resistance? Why?

Answer 21

Upper Respiratory tract

Smallest cross sectional area!

Cross sectional area in bronchioles is much higher, as there are so many of them, giving lower resistance.

(Even though an individual bronchioles has a small cross section)

Question 22

Which conditions can cause increased airways resistance?

Answer 22

Increased mucus. (e.g. asthma/ CF)

Hypertrophy of smooth muscles/ oedema.

Loss of radial traction (attachments of bronchioles to alveoli (parenchyma) which holds them open)