Physiology: ventilation and compliance

Question 1

Which cells produce surfactant?

Answer 1

Type 2 pneumocytes

Question 2

What is the main action of surfactant?

Answer 2

To reduce surface tension in the alveoli. Most effective in the small alveoli as surfactant molecules are more concentrated.

Question 3

What would happen if there was no surfactant?

Answer 3

Inwardly directed pressure would cause small alveolar collapse and air would collect in the large alveoli. Law of La Place.

Question 4

List the 3 main actions of surfactant.

Answer 4

Reduces the tendency of the lungs to recoil, increases compliance and makes the work of breathing easier.

Question 5

What is IRDS and what causes this?

Answer 5

Infant respiratory distress syndrome. Caused by no surfactant due to premature birth.

Question 6

Define compliance.

Answer 6

Change in volume relative to change in pressure. A measure of how stretchy (not elastic) the lungs are.

Question 7

Describe high vs low compliance.

Answer 7

High compliance means there can be high volume changes with low pressure changes. Low compliance means that low volume changes cause high pressure changes.

Question 8

Define functional residual capacity (FRC).

Answer 8

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

Question 9

Which requires most effort, inspiration or expiration?

Answer 9

Inspiration as elastic recoil and surface tension need to be overcome,

Question 10

At which part of the lungs is compliance best?

Answer 10

Base and least at the apex as alveoli are more inflated at the FRC. Alveolar ventilation also declines from base to apex.

Question 11

Why is compliance least at the apex?

Answer 11

At the base of the lungs, alveoli are squashed between the weight of the lung and the diaphragm, therefore they have more opportunity to expand during respiration. Small changes in intrapleural pressure bring about a larger volume change at the base compared to the apex. Patient turned of their side? Compliance best on the side they are lying on.

Question 12

Define Pt (transpulmonary pressure).

Answer 12

Difference between PA (alveolar pressure) and Pip (intrapleural pressure). Always positive.

Question 13

What is the difference between an obstructive or restrictive lung disease?

Answer 13

In obstructive lung diseases there is an obstruction of airflow, especially on expiration. In restrictive lung diseases there is a loss of lung compliance, lung stiffness and incomplete lung expansion.

Question 14

Give 2 examples of obstructive lung diseases.

Answer 14

Asthma and COPD (chronic bronchitis and emphysema).

Question 15

Give 4 examples of restrictive lung diseases.

Answer 15

Fibrosis, IRDS, oedema and pneumothorax.

Question 16

Define spirometry.

Answer 16

Static is when the only consideration is the volume of air exhaled. Dynamic is when the volume of air exhaled is measured against a certain time.

Question 17

What is FEV1:FVC?

Answer 17

Forced expiratory volume in 1 second vs forced vital capacity. The amount of air expired in 1 second vs the total amount of air expired. This should be 80% or 4L:5L in fit, healthy males. This tests elasticity of lungs.

Question 18

How would FEV1:FVC change in obstructive lung disease?

Answer 18

Problem is air getting out of the lungs, so FEV1 would be low. This would mean the ratio would be low.

Question 19

How would FEV1:FVC change in restrictive lung disease?

Answer 19

No real problem getting air out, just not much air in the lungs to begin with. Ratio can be around 90% but volumes will be lower. This can seem normal so need other tests.

Question 20

What is FEF?

Answer 20

Forced expiratory flow. Average expired flow over the middle of a FVC.

Question 21

What is anatomical dead space?

Answer 21

Air in the conducting airways that cannot participate in gas exchange.

Question 22

Define tidal volume.

Answer 22

Volume of air breathed in and out of the lungs, 500ml in 500ml out.

Question 23

Define IRV and ERV.

Answer 23

IRV is the maximal amount of air than can be drawn in to the lungs - 3L. ERV is the maximal amount of air that can be pushed out from the lungs - 1L.

Question 24

Define RV.

Answer 24

Residual volume. The amount of air in the lungs at the end of a maximal expiration - 1.2L. Allows gas exchange to occur between breaths.

Question 25

Define VC.

Answer 25

Maximal amount of air a person can expire at the end of a maximal inspiration (TV + ERV + IRV).

Question 26

Define TLC.

Answer 26

VC + RV.

Question 27

Define inspiratory capacity (IC).

Answer 27

IRV + TV.

Question 28

What are the 2 types of ventilation?

Answer 28

Pulmonary and alveolar.

Question 29

Describe the breathing cycle.

Answer 29

500ml of air is expired - 350ml of this is coming from the lungs and 150ml is coming from anatomical dead space (stale air). On inhalation, 150ml of stale air from dead space is taken into the lungs and 350ml of fresh air is taken into the lungs. For every 500ml breathed in, 150ml never reaches the alveoli - breathing is only 70% efficient.

Question 30

What is alveolar ventilation?

Answer 30

(TV - dead space) x respiratory rate

Question 31

Describe difference between a normal, anxious and relaxed patient.

Answer 31

Normal: TV 500ml, RR 12 breaths/min, total pulmonary ventilation 6L/min, alveolar ventilation 4.2L. Anxious: TV 300ml, RR 20, pulmonary 6L, alveolar is 3L (hypoventilation). Relaxed: TV 750ml, RR 8, pulmonary 6L, alveolar 5.8L (hyperventilation).

Question 32

Define partial pressure.

Answer 32

The pressure of a gas in a mixture of gases is equivalent to the percentage of that gas in the mixture X by pressure of the whole mixture.

Question 33

What is atmospheric pressure?

Answer 33

101 kPa (760 mmHg).

Question 34

What is the partial pressure of O2 in the air?

Answer 34

21 kPa (160 mmHg).

Question 35

What are PO2 and PCO2 in the alveoli?

Answer 35

PO2 is 100 mmHg and PCO2 is 40 mmHg. Hypoventilation: PO2 decreases and PCO2 increases. Hyperventilation: PO2 increases and PCO2 decreases.