Nunn's Chapter 3

Question 1

What causes respiratory system volume to decrease

Answer 1

Elastic forces of lung cause resp system to want to collapse. An isolated lung prep will collapse til all air is expelled

Question 2

What causes respiratory system volume to decrease

Answer 2

Thoracic cage wants to expand. Will expand to 1 litre above FRC if chest is opened. This force counteracts the lungs desire to colpse

Question 3

5 factors that impede CHANGES in lung volume

Answer 3

1-elastic resistance of lung and chest wall

Question 4

What are the “frictional resistances”? (3)

Answer 4

frictional resistance to gas flow

Question 5

What are the “elastic resistances”?

Answer 5

elastic resistace of lung and chest wall (“elastance”)

Question 6

Define lung compliance

Answer 6

change in lung volume per unit change in transmural pressure gradient (diff between alveolar and pleural pressures)

Question 7

normal values of lung compliance

Answer 7

150 ml/cmH2O

Question 8

difference between static and dynamic compliance

Answer 8

static - measured when volume held fixed (no flow)

Question 9

How do we show that surfactant improves compliance?

Answer 9

immersion in saline decreases elastance

Question 10

What is Law of Laplace, how does surfactant alter this?

Answer 10

P = 2T/R

Question 11

Why is surfactant important for alveolar stability

Answer 11

Decreases tendency of small alveoli to get smaller and decreases tendency of big alveoli to get bigger (which is what Law of Laplace predicts. Surfactant modifies it’s own surface tension to counteract this

Question 12

What is surfactant made of, and made where?

Answer 12

80% dipalmitoyl phosphatidylcholine (hydrophobic)

Question 13

Problems with bubble model of surfactant?

Answer 13

i) if liquid layer in alveoli is contiguous and continuous, how can tension vary?

Question 14

Alternates to bubble model of surfactant?

Answer 14

Hill’s morpological model - discontinuous, and forms wet and dry areas

Question 15

Draw transmural pressure gradient t different lung volumes

Answer 15

…

Question 16

What are the differences in alveolar size and transmural pressures at different heights in the lung? What is the gradient in TMP (amount).

Answer 16

upper lung alvoli are larger and have a higher transmural pressure gradient than lower ones, as pleural pressure is less. Grient in TMP, and peural pressure, is about 1cm per 3cm of depth n healthy lung.

Question 17

what does “time dependence of pulmonary elastic behavior” mean?

Answer 17

when a lung is inflated, pressure drops initially, due to gas flow and viscoelastic energy redistribution. Essentially it is the difference between dynamic and static compliance. This is effected by respiratory rate

Question 18

What is hysteresis? Effect of tidal volume size on hysteresis?

Answer 18

P-V curves between inflation and deflation are different. Imply that it takes slightly more energy than expected to inflate lungs, and slightly less energy is released during expiration than is expected.

Question 19

Causes of time dependence of pulmonary elastic behavior?

Answer 19

1) Surfactant activity - surface tension is greater at lrger lung volumes

Question 20

List 8 factors that effect LUNG compliance

Answer 20

1 - lung volume. Can make constant by expressing as “specific compliance” (compliance/FRC)

Question 21

3) What are normal values?

Answer 21

1) need all muscles to be relaxed - difficult to acheive with diaphragm, as it has some resting tone. Therefore paralysis is best option

Question 22

Factors that alter thoracic cage compliance

Answer 22

Ribs - ossification

Question 23

Formula for total compliance of resp system. Values in paralysed patient?

Answer 23

1/Ctotal = 1/Clung + 1/Cthoracic cage

Question 24

Formula for resp system elastance? Normal values?

Answer 24

Etotal = Elung + Ethoracic cage

Question 25

2) Residual Volume

Answer 25

1) TLC = volume of gas at end of maximal voluntary inspiration. Balance of forces. At end-insp., expiratory musces are contracting strongly

Question 26

2) Factors effecting FRC?

Answer 26

1 - lung vol at end of normal expiration

Question 27

Draw diagram of static lung volumes

Answer 27

…

Question 28

Define closing capacity

Answer 28

reduction in lung volume below a

Question 29

Relationship between FRC and closing capacity and age and body position

Answer 29

FRC decreases with supine position, while CC doesn’t, therefore CC will exceed FRC in some pts - causing shunt during normal breathing and therefore hypoxia. Seen in anesthesia and ICU

Question 30

Effect of age on FRC and CC relationship.

Answer 30

CC increases with age and can eventually equal FRC. In upright position, this occurs at 66 years, in supine at 44 years. Causes decrease on arterial PaO2 with normal aging.

Question 31

How is compliance calculated? What pressure values are used for transpulmonary and chest wall compliances?

Answer 31

Change in volume divided by change in pressure gradient.

Question 32

How is pleural pressure measured?

Answer 32

Assumed to be equivalent to esophageal pressure. By convention, 32-35cm beyond nares.

Question 33

Best subject positions for measuring lung and total compliance?

Answer 33

upright is best for lung compliance. Supine and paralysed for total compliance.