4-Gas Exchange Flashcards
atmospheric pressure
weight of gas molecules from gravity pulling towards earth
-dec as go higher, inc as closer to earth
-density of air less higher in atmos
760 mmHg
partial pressures
calculate by multiplying fractional concentration x atmos P
air is mostly nitrogren + some oxygen + others
daltons law
total P of a mixture of gases = sum of partial pressures of component gases
effect of water vapor on partial pressure
subtract water vapor P from total atmos P THEN multiply by fractional concentration
PH20 = 47 mmHg so 760-47
primary driving force of diffusion
pressure gradient
rate of diff = (cross section area x diffusion coefficient x pressure gradient) / thickness of membrane
partial pressure trends
O2 and CO2 diffuse downhill along gradients
-CO2 in oppo direction tho
henry’s law
solubility of gas in a liquid (oxy in blood) directly proportional to partial P of gas above liquid
-higher PP in lungs then higher in blood
aqeous gas = partial pressure gas x constant
gas exchange driven by what
diffusion and perfusion
pressures in dry inspired air
O2 = 160
CO2 = 0
pressures in humidified air trachea
O2 = 150
CO2 = 0
pressures of alveolar air
O2 = 100
CO2 = 40
alveolar capillary membrane
blood PCO2 equil rapidly unless heavy exercise so venous PO2 lower and blood flow faster
O2 diffusion to tissues
@ arterial capillary = 95/100
@ venous end = 40 mmg
tissue PO2 balanced by
oxygen consumption and delivery
-if inc consumption then dec PO2 if delivery not inc proportionally (exercise)
CO2 diffusion
arterial end capillary = 40 mmHg
tissue = 45 mmHg
venous end = 45 mmHg
CO2 balance
CO2 production = tissue metabolism
CO2 removal = blood flow to tissue and uptake by blood
if inc oxy consumption may inc in PCO2 if removal CO2 not inc proportionally
atelectasis
collapse of alveoli = affect P gradient
dec cross sectional area for diffusion = dec rate
pneumonia
inc diffusion distance/thickness bc inflammation or bacteria
pulmonary edema
inc diffusion distance/thickenss
inc fluid in intersitial space
pulmonary fibrosis
inc diffusion distance/thickness
simplified alveolar gas equation
based on arterial PO2 then compare to calculated value
prediction of gas exchange status (tells quality of respir membrane and therapeutic decision)
normal ranges of PaO2
5-20mmHg for person up to middle age
diffusing capacity DLCO
measure lung ability to transfer gas
-dep on both diffusion of gas and interaction with Hb
admin known amount of CO to see how much consumed by Hb
factors that affect DLCO
anything that affects membrane
-thicken membrane = dec DLCO
-emphysema, fibrosis, interstitial lung dz, pulm hypertension
anemia and polycythemia = inc DLCO
