Gaseous Diffusion & Transport I #1 Flashcards
What is FO2 + PO2?
- FO2: franctional conc/% of O2 = 0.21/21%
- PO2 = partial P of O2
What is PB?
Barometric (atmospheric) P
What is PIO2 + FIO2?
- PIO2: PO2 in inspired gas (usually in trachea)
- FIO2: FO2 in inspired gas
What is PAO2 + FAO2?
- PAO2: PO2 in alveoli
- FAO2: FO2 in alveoli
What is PaO2 + FaO2?
- PaO2: PO2 in arteries
- FaO2: FO2 in arteries
List the common P + SI units
- common P: mmHg
- SI: kPa
What is dead space?
airway vol with no gas exchange
What is anatomic dead space?
all resp tract except alveoli + resp bronchioles
What is physiologic dead space?
all anatomical areas + areas where gas exchange dysfunctional
What is Dalton’s law?
PP of gas in mix is P it would exert if occupied the vol alone
What is the total P of air?
- is gas mix
- total P of all gases in it = PB
What is PB made up of?
PO2 + PCO2 + PN2 (includes all inert gases) + PH2O
How can calc PP of a gas?
fractional conc x PB
What is PB at sea level?
101 kPa (760mmHg)
What is FO2 (in dry air)?
- all H2O vapour removed
- 0.209 / 21%
How do you calc dry PO2?
FO2 = 0.209 x PB = 101
= 21kPa (159mmHg)
How does PB change at altitude?
red e.g. to 33kPa on top of Everest
How does FO2 change at altitude?
unchanged but P it exerts changes
How does PIO2 change at altitude + consequence?
- PIO2 (= FIO2 X PB) falls progressively with inc altitude when breathing air
- need supplemental O2 to inc FIO2 to compensate for dec PB
What happens as PP of gas e.g. CO2 above liquid is increased?
- the more the gas will dissolve in the liquid
- so need to inc PP of gas to get it to dissolve
What happens when P released from liquid?
- less gas held in sol
- bubbles of gas will rise from liquid bc they’re no longer dissolved
What does the amount if gas dissolved in liquid depend on when given PP applied?
sol of gas in liquid
What happens to gas in a flask filled partially with liquid?
- if gas dissolved in liquid - exerts PP + so leave surface of liquid until PP of gas in liquid = P of gas in gas phase
- if gas was already in gas phase, move into liquid in same way until both P are equal + reach P equ
What is the PP of X gas in gas equal to in the flask?
PP of X gas in liquid
At equ, how much gas is in liquid in the flask?
- depends on sol of gas in liquid
- gas with low sol dissolve poorly in liquid even at high PP
- content of gas in liquid low even though PP might be high
How can you inc content of gas in liquid?
- need to inc sol (can’t bc its constant) so need to inc PP
What is gas transfer between diff phases e.g. gas + liquid, blood + fat, alv + cap etc determined by?
PP gradient not conc gradient
What does the PP of gas in liquid depend on?
- conc of gas mol in liquid (ml/ml or mmol/l)
- sol of gas in liquid
What is Henry’s law?
content of gas (ml/l) in liquid = sol (ml/l/kPa) x PP (kPa)
What is difference between high + low sol gas in liquid?
- high sol: not going to exert much PP
- low sol: need high PP as its fighting to escape
- less sol gas has high PP, more sol gas has low PP
What does H2O vapour P (PH2O) depend on?
- temp
- sat
How does sat H2O vapour P change?
rises with inc temp
What does % sat H2O vapour depend on?
how much H2O air has been in contact with
What happens to air as it enters the lungs?
passes over moist surfaces + becomes 100% sat
Why is H2O vapour P in lungs constant?
Alveolar temp constant bc body temp constant (37 degrees) + H2O vapour P depends on temp
What is PIO2 + how is it calc?
= PO2 of moistened inspired air at end of trachea
= (PB - 6.3) x 0.209 kPa or (PB - 47) x 0.209 mmHg
Why can’t measure PAO2 directly?
- CO2 diffuses into alveolus to replace O2 diffusing into pul cap
- if 1 mol of CO2 prod for each mol of CO2 used then PAO2 = PIO2 - PACO2
What is the alveolar gas equation?
PAO2 approx PIO2 - PACO2/R bc more O2 used than CO2 prod
What is resp quotient?
- CO2 prod/O2 consumption
- usually 0.8
What inc diff between alveolar + inspired O2?
inc CO2
Why does PO2 inc when overbreathe?
PACO2 dec
