Alveolar ventilation and gas diffusion (physiology)

Question 1

What is the volume of total lung capacity?

Answer 1

3L

Question 2

What is tidal volume and the exact volume?

Answer 2

Air we breath in/out when rested (1/2 total lung capacity)
500ml

Question 3

What is the volume of residual

Answer 3

1L - 1.2L
Cannot be exhaled, keeps alveoli open

Question 4

What is the volume of inspiratory reserve volume?

Answer 4

3L

Question 5

What is the volume of expiratory reserve volume?

Answer 5

1.1L

Question 6

Volume of anatomical dead space?

Answer 6

150 ml

Question 7

Define pulmonary ventilation

Answer 7

Total movement of air in/out of lungs
(relatively insignificant in functional terms)

Question 8

Define alveolar ventilation

Answer 8

Volume of fresh air getting to alveoli ad therefore available for gas exchange
(functionally more significant)

Question 9

What is the impact dead space has on alveolar ventilation

Answer 9

Dead space volume doesn’t change (always 150ml of dead space)

(from google)
Dead space is the volume not taking part in gas exchange and, if increased, could affect alveolar ventilation if there is too low a delivered volume.

Question 10

What are the normal values for alveolar and systemic arterial gas partial pressure?
(O2 and CO2)

Answer 10

In normal ventilation alveolar pp = systemic pp at 4.2L/min
Normal alveolar partial pressure of O2 = 100mmHg (13.3 kPa) = systemic arterial PO2
Normal alveolar partial pressure of CO2 = 40mmHg (5.3 kPa) = systemic arterial PCO2

Question 11

What vessels carries blood to the lungs and away?

Answer 11

Heart to lungs = pulmonary artery (deoxygenated blood)
Lungs to heart = pulmonary vein (oxygenated blood)

Question 12

Define pulmonary circulation (in sense of gas exchange)

Answer 12

Pulmonary circulation supplies dense capillary network surrounding alveoli.
Returns oxygenated blood to the left atrium and receives deoxygenated blood from tissues.

Question 13

What factors influence rate of diffusion of gasses across the alveoli?

Answer 13

Partial pressure of gases
Gas solubility
Surface area
Thickness of membrane
Distance between alveoli and capillary

Question 14

What does the a in PaO2 mean?

Answer 14

Arterial blood
(partial pressure of oxygen in arterial blood)

Question 15

What does the A in PAO2 mean?

Answer 15

Alveolar
(partial pressure of oxygen in alveolar air)

Question 16

What does the v in PvO2 mean?

Answer 16

Mixed venous blood
(partial pressure of oxygen in mixed venous blood)

Question 17

Values for partial pressures?

Answer 17

See sheet :)

Question 18

Describe emphysema?
(what causes it, effect on gas exchange, effect on lung compliance)

Answer 18

Main cause = smoking

Causes a reduction in surface area of alveoli meaning less diffusion. Less O2 enters blood so lower PO2 in blood.

Increased compliance making inspiration really easy but expiration is a struggle. Due to a breakdown in elastic fibres and thus lack of contraction/elastic recoil to aid expiration.

Question 19

Describe fibrotic lung disease?
(what causes it, impact on diffusion, effect on lung compliance)

Answer 19

Thickening of the alveolar membrane.

Less O2 can diffuse across thick mem so lower PO2 in blood.

Decreased lung compliance as fibrous tissue resists stretch so inspiration is a struggle (trying to inflate the alveoli/overcome that resistance)

Question 20

Describe asthma?
(affect on ventilation, what is overall effect)

Answer 20

Increases airway resistance and decreases airway ventilation

Smooth muscle in airways overly contracts making it harder to expire.
(since during expiration airways contract even further).

Less O2 in alveoli so low PO2 in alveoli and in blood.

Question 21

Describe pulmonary oedema?
(Causes, impact on diffusion)

Answer 21

Fluid builds up between alveoli and capillaries increasing diffusion distance.

This reduces PO2 in blood (O2 is insoluble so struggles to diffuse across fluid)

Question 22

Outline the basic characteristics of obstructive lung disease?

Answer 22

Obstruction of airflow
Affects expiration (where airways constrict)

Question 23

Outline the basic characteristics of restrictive lung disease?

Answer 23

Restriction of lung expansion
Affects inspiration
Gives loss of lung compliance

Question 24

Give examples of obstructive lung diseases (2)

Answer 24

Asthma:
- Reduces airway radius meaning greater constriction during expiration
COPD: (also reduces airway radius)
- Chronic bronchitis - inflamed bronchi
- Emphysema - destruction alveoli, loss elasticity (no elastic recoil)

Question 25

Give examples of restrictive lung diseases (4)

Answer 25

Fibrosis
- Resists stretch during inspiration
- Idiopathic or asbestosis
IRDS
- Babies born premature <36 weeks
- Insufficient surfactant produced so surface tension of alveoli is too great and they collapse
- Increases the work of inspiration
Oedema
- Fluid resists alveoli inflation
Pneumothorax
- Air in pleural cavity
- Visceral and parietal membrane pulled apart so lung no longer attached to chest wall
- Complete loss of lung expansion

Question 26

What does spirometry measure?

Answer 26

Measures the volume of air we exhale

Question 27

How can spirometry be used to measure normal lung function?

Answer 27

FEV1/FVC test:

Forced expiratory volume in 1s/ Forced vital capacity

Normal value = 4.0L/5.0L = 80%

Question 28

What results of a lung function test would you expect to see in a patient with obstructive lung disease?

Answer 28

LOWER ratio
FEV1/FVC = 1.3/3.1 = 42%

Takes longer to get air out of lungs so big reduction in FEV1 but less of an effect on FVC

Question 29

What results of a lung function test would you expect to see in a patient with restrictive lung disease?

Answer 29

SAME/HIGHER ratio
FEV1/FVC = 2.8/3.1 = 90%

Absolute air flow rate is reduced
Total volume reduced due to limited lung expansion.