pulmonary gas exchange

Question 1

what are the balues of PaO2 and CO2 in reso faikyre

Answer 1

type 1 - paO2 <8kPa and co2 is notmal or low

type 2 - PaCO2 >6.5 and o2 is usuallt low

Question 2

what mechanisms contribute to hypoxaemi

Answer 2

ventilation/perfusion imbalance - VQ
diffusion impairment
alveolar hupoventilation
shunt

Question 3

what is V/Q mismatch

Answer 3

commonest cause of hupoxaemia

low V/Q in some albeoli arises due to loval albeolar hupoventolation fue to some focal fisease

Question 4

what is shuny

Answer 4

blood passing from right to left side of heart without contacting ventikated alveoli
pathologicak shunt in AV malformations, congenital heart disease and pulmonary disease
large shunts respond poorly to increased in FIO2
blood leaving normal lung is alreaddy 98% sat

Question 5

why do patients have hypoxaemia in pneuominia

Answer 5

• vent/perf mismatch - bronchitis and bronchopneuomonia —— some vent of abnormal alveoli but not enough
• shint - sever bronchopneuomonia, lobar patter with large areas of consilidstion —- no vent of abnormal albeoli

Question 6

what is alveolar hypocentilation

Answer 6

amount of air moved in and out of lungs
it increases PACO2 and this increases PaCO2
decreases PAO2 and paO2 falls
this is corrected ny increaseing tje fraction of aur inspired whcih is oxygen

Question 7

what can leas to alveolar hypoventilation

Answer 7

chest wall damafe
muscle paralysis and diaphragmatic damage
neurological problems w breathing - peripheral nerve damage or loss of function
CNS malfunction - opiate poisoning, COPD

Question 8

why may u get hupocaemia in COPD

Answer 8

v/q mismatch: airway obstruction +/- bronchipneumonia
diffusion impairment: loss of alveolar surface area in emphysema
alveolar hypoventilation: reduced respuratory drive
shunt: only during acute exacerbation if pneumonia is extensive enough

Question 9

what does gas flow through a membrane depend on

Answer 9

thickness and surface areas of membtane and gas pressure across it

Question 10

does CO2 or O2 diffuse faster

Answer 10

CO2 diffuses 20 times faster than O2 due to greater solubility
diseases impairing gas diffusion usually do NOT change CO2 levels

Question 11

what does diffusion impairment mean

Answer 11

it takes longer for blood and alveolar air to ewuilibrate particularly for o2

Question 12

how long does equilibration normally take

Answer 12

0.25sevonds

capillary transit time normally 0.75 seconds at rest

Question 13

how may hypoxaemia be corrected

Answer 13

by increasing FIO2. this increased PAO2, this increasing rate of diffusion. rarely clinically the sole cause of hypoxaemia