7. Alveolar ventilation & pulmonary gas exchange

Question 1

Which alveoli are suspended?

Answer 1

Apical alveoli - top ones

Question 2

Which alveoli are smaller? Effect on Pleural Pressure?

Answer 2

Lower alveoli less –ve Ppl

Question 3

Which alveoli are bigger? Effect on Pleural Pressure?

Answer 3

Top alveoli more –ve Ppl

Question 4

Where is ventilation greatest in the lung?

Answer 4

bottom of lung

Question 5

How is regional ventilation measured?

Answer 5

Upright individual Inhales radioactive Xenon gas Radiation recorded from ventilated areas

Question 6

Gas transfer between alveoli and blood: the barrier

Answer 6

3 layers: Alveolar epithelium Capillary endothelium Interstitium (sometimes absent)

Question 7

Thin portions of barrier

Answer 7

Gas exchange takes place

Question 8

Thick portions of barrier

Answer 8

Fluid exchange takes place

Question 9

Dalton’s law of partial pressures

Answer 9

Total pressure x Fractional concn in mixture

Question 10

Henry’s law

Answer 10

The concentration of gas in a liquid is proportional to its partial pressure

Question 11

Fick’s law: diffusion is proportional to

Answer 11

1) Area 2)Partial pressure gradient 3)Diffusion constant

Question 12

Fick’s law: diffusion is Inversely proportional to

Answer 12

1) Barrier thickness

Question 13

How long does blood take to traverse a pulmonary capillary at rest?

Answer 13

0.75 seconds

Question 14

Effects of reduced transit time?

Answer 14

Strenuous exercise increases cardiac output May not have time for complete equilibrium to occur

Question 15

Effects of increased barrier?

Answer 15

Pulmonary oedema Fibrosis

Question 16

What limits the amount of gas we can get into the blood?

Answer 16

1) CO 2) Nitrous Oxide 3) O2 uptake

Question 17

CO bound avidly by Hb

Answer 17

Little in solution

not much rise in PCO

Still diffusing at end of capillary

DIFFUSION LIMITED

Question 18

N2O just stays in solution

Answer 18

No binding

rapid rise in PN2O in blood

partial pressure gradient lost

Net diffusion stopped before end of capillary

FLOW LIMITED

Question 19

O2 intermediate: lots bound

Answer 19

Normally FLOW LIMITED

Can be diffusion limited in disease

Question 20

Diffusion in the lung is decreased by:

Answer 20

1) Decreased SA (emphysema) 2) Increased membrane thickness (pulmonary fibrosis) 3) Pulmonary hypertension 4) Anaemia

Question 21

Diffusion in the lung is increased by:

Answer 21

1) Exercise just before the test 2) Supine position 3) Asthma 4) Pulmonary haemorrhage 5) Polycythaemia (too many rbcs) 6) Mild left heart failure