2. Alveolar Gas Exchange

Question 1

when air flows thru a tube, the air resistance makes —

Answer 1

airflow more difficult

Question 2

if airway resistance is high, what is needed from Ms

Answer 2

more effort to produce air flow

(overall airflow is slower)

Question 3

what is the equation for resistance

& what changes resistance the most

Answer 3

radius change = greatest impact on resistance

Question 4

what controls the bronchiole diameter

Answer 4

Sm. M

• change airway resistance

Question 5

why do you need to change airway resistance

Answer 5

send air to right places & away from areas w/o oxygenations

(right places = alveoli that have good supply & good oxygenation)

Question 6

what is alveolar ventilation

Answer 6

volume of air reaching the alveoli

Question 7

what is V_A(dot) & what is the average value

Answer 7

ventilation per min –> V_A * F

4 L/min

Question 8

What is perfusion

Answer 8

similar to cardiac output

normal vol = 5 L/min

Question 9

what is the equation that helps you determine rate of diffusion

Answer 9

Question 10

what are the normal J-values for O2 & CO2?

Answer 10

O2 = 250 mL exchanged every min

CO2 = 200 mL exchanged every min

(Rmr each are evaluated differently)

Question 11

which factors influence diffusion rate and depend directly on the structure of the alveolus

Answer 11

SA = # of alveoli in lung (specifically # of caps available

& distance: diffusion distance

Question 12

how does SA vary

& what happens if it increases

Answer 12

at rest = 70 mL in pul cap

during exercise = up to 200 mL of blood in caps

• ALL DEPENDS ON NUMBER OF OPEN PUL CAPS

–> if SA increases - J increases

Question 13

what happens to alveoli in COPD and emphysema

Answer 13

lost alveoli –> decreased SA –> decrease ability to get O2 in (decreased diffusion rate)

Question 14

what affects the distance btn alveoli and caps?

what is the avg

Answer 14

fluid layer, alveolar epithelium, interstitial space, blood vessel wall

avg = 0.6 micron

Question 15

what happens when you have deposition of collagen w/i interstitial spaces

Answer 15

increase diffusion distance –> decreases diffusion rate

-happens in interstitial lung disease-

Question 16

What does the diffusion coefficient depend on

Answer 16

1. solubility of the gas in h2o (CO2 more soluble = advantage)
2. molecular weight of gas (O2 = lighter = advantage)

Question 17

what is the difference of diffusion constant for CO2 and O2

Answer 17

D_CO2 (20x) D_O2

• which means CO2 will cross even if O2 has difficulty crossing

Question 18

where is the P gradient for O2 the highest

Answer 18

at start of cap

P_capO2 = 40 mmHg & P_alvO2 = 104 mmHg

gradient = 60 mmHg & O2 flows into caps

Question 19

when is the pressure gradient for CO2 the highest

Answer 19

P_capCO2 = 45 mmHg & P_alvCO2 = 40 mmHg

gradient = -5 mmHg; so CO2 flows out of cap

Question 20

how long does it take O2 to equilibrate as the RBC flows thru pul caps?

What does it depend on

Answer 20

0.25 sec ==> perfusion limited

depends on perfusion

Question 21

what happens to RBC movement thru pul cap during exercise

how can this be a prob

Answer 21

RBC spends just enough time to get to O2 equilibrium

if you have lung disease - you notice problems with exertion bc dont spend enough time to equilibrate –> becomes diffusion limited bc sending more blood doesn’t help

*1st sign of lung disease - difficulty w/ exercise*

Question 22

what is DL_O2

Answer 22

diffusion capacity of lung for O2

= 21 mL O2/min/mmHg at rest

Question 23

how do you measure DL_O2

Answer 23

use Carbon monoxide (CO)

-it binds to only Hb (none in plasma) so you can administer very small amount of CO and measure how much is exhaled –> then multiple by 1.23 (correction factor)

*cant measure O2 directly bc som bind to Hb and some dissolve in plasma*

Question 24

what is the average amount of time a RBC spends in a pul cap

Answer 24

0.75 secs

Question 25

how fast does CO2 equilibrate as RBC flows thru cap

how is this affected in lung disease

Answer 25

almost immediately (bc its so soluble) - thats why..

have to have very SEVERE case of lung disease for CO2 for be affected (have problems w/ O2 first)

Question 26

what is LaPlace’s Law

Answer 26

Pressure = 2T/r

P is dependent on r bc T is the constant surface tension

Question 27

what happens if you dont have surfactant

Answer 27

large alveoli have low P & small alveoli have high P

so you build a P gradient and air from the small alv flow into large ==> poor lung inflation & collapsed alveoli!

Question 28

what does surfactant do

Answer 28

it reduces the surface tension (T) in small alveoli

so the Ps of small and large alveoli match and small ones dont have collapse

*help maintain different sized alveoli

Question 29

what are components of surfactant and where is it stored

Answer 29

phospholipid: DPPC & proteins (SPA, SPB SPC, SPD) –> SPB imp in fxn

stored in intracelluar lamellar bodies (granules w/ high [DPPC] & [SPB])