2. Alveolar Gas Exchange Flashcards
when air flows thru a tube, the air resistance makes —
airflow more difficult
if airway resistance is high, what is needed from Ms
more effort to produce air flow
(overall airflow is slower)
what is the equation for resistance
& what changes resistance the most
radius change = greatest impact on resistance
what controls the bronchiole diameter
Sm. M
- change airway resistance
why do you need to change airway resistance
send air to right places & away from areas w/o oxygenations
(right places = alveoli that have good supply & good oxygenation)
what is alveolar ventilation
volume of air reaching the alveoli
what is VA(dot) & what is the average value
ventilation per min –> VA * F
4 L/min
What is perfusion
similar to cardiac output
normal vol = 5 L/min
what is the equation that helps you determine rate of diffusion
what are the normal J-values for O2 & CO2?
O2 = 250 mL exchanged every min
CO2 = 200 mL exchanged every min
(Rmr each are evaluated differently)
which factors influence diffusion rate and depend directly on the structure of the alveolus
SA = # of alveoli in lung (specifically # of caps available
& distance: diffusion distance
how does SA vary
& what happens if it increases
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
what happens to alveoli in COPD and emphysema
lost alveoli –> decreased SA –> decrease ability to get O2 in (decreased diffusion rate)
what affects the distance btn alveoli and caps?
what is the avg
fluid layer, alveolar epithelium, interstitial space, blood vessel wall
avg = 0.6 micron
what happens when you have deposition of collagen w/i interstitial spaces
increase diffusion distance –> decreases diffusion rate
-happens in interstitial lung disease-
What does the diffusion coefficient depend on
- solubility of the gas in h2o (CO2 more soluble = advantage)
- molecular weight of gas (O2 = lighter = advantage)
what is the difference of diffusion constant for CO2 and O2
DCO2 (20x) DO2
- which means CO2 will cross even if O2 has difficulty crossing
where is the P gradient for O2 the highest
at start of cap
PcapO2 = 40 mmHg & PalvO2 = 104 mmHg
gradient = 60 mmHg & O2 flows into caps
when is the pressure gradient for CO2 the highest
PcapCO2 = 45 mmHg & PalvCO2 = 40 mmHg
gradient = -5 mmHg; so CO2 flows out of cap
how long does it take O2 to equilibrate as the RBC flows thru pul caps?
What does it depend on
0.25 sec ==> perfusion limited
depends on perfusion
what happens to RBC movement thru pul cap during exercise
how can this be a prob
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*
what is DLO2
diffusion capacity of lung for O2
= 21 mL O2/min/mmHg at rest
how do you measure DLO2
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*
what is the average amount of time a RBC spends in a pul cap
0.75 secs
how fast does CO2 equilibrate as RBC flows thru cap
how is this affected in lung disease
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)
what is LaPlace’s Law
Pressure = 2T/r
P is dependent on r bc T is the constant surface tension
what happens if you dont have surfactant
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!
what does surfactant do
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
what are components of surfactant and where is it stored
phospholipid: DPPC & proteins (SPA, SPB SPC, SPD) –> SPB imp in fxn
stored in intracelluar lamellar bodies (granules w/ high [DPPC] & [SPB])
