GMS6402 CORE EXAM MANUAL 2025/2026 QUESTIONS
AND SOLUTIONS GRADED A+ TIP
✔✔rate of diffusion of a gas is proportional to what and inversely proportional to what -
✔✔proportional to area of membrane
inversely to thickness
✔✔what is Fick's law of diffusion for the lung - ✔✔Dl x deltaP
Dl = diffusion capacity of lung for a gas (includes surface area, thickness, solubility, and
weight)
deltaP = pressure gradient
✔✔how do we measure Dl in the clinic - ✔✔use CO, diffusion limited
= V. / deltaP
✔✔where is most of the surface area of the lungs located - ✔✔alveoli air spaces
bc surface area is large and walls are thin
✔✔what governs the movement of gases across the pulmonary membrane - ✔✔Fick's
Law
✔✔perfusion limited - ✔✔gas is limited by pulmonary blood flow
reaches equil. when leaves pulmonary capillaries, so very quickly
example: N2O (nitrous oxide)
✔✔diffusion limited - ✔✔gas is limited by properties of the blood-gas barrier or the gas
itself
never reaches equilibrium
when Dl is low
example: CO, carbon monoxide
✔✔how to fix perfusion limited - ✔✔increase number of RBCs/ increase blood flow
✔✔is oxygen perfusion or diffusion limited - ✔✔perfusion
, depends on blood flow
reaches equilibrium when 1/3 way through capillary bed
✔✔what is the capillary reserve time (CRT) - ✔✔the portion of the erythrocyte transit
time in which no further diffusion of oxygen occurs
✔✔when does diffusion limitation of oxygen happen - ✔✔when Dl is reduced in disease
with exercise, bc RBC time in pulmonary capillary is reduced
✔✔what affects the Dl - ✔✔changes in Hb content
rate at which O2 combines with Hgb
✔✔what diseases decrease Dl - ✔✔pulmonary fibrosis (thicker barrier, less SA)
loss of functional lung tissue (tumor) (less SA)
emphysema (less SA)
anemia (less Hb content)
pulmonary edema (thicker barrier)
✔✔is the Dl of CO2 greater or less than that of O2 - ✔✔greater (5x)
✔✔is CO2 usually perfusion or diffusion limited - ✔✔perfusion
✔✔is oxygen diffusion limited before or after CO2 - ✔✔before
✔✔what is the formula for the total amount of O2 in the blood - ✔✔dissolved O2 +
HbO2
usually around 20 mls O mls of blood
✔✔what is the value for the solubility of O2 (constant) - ✔✔0.003 mls O2 / mm Hg / 100
mls blood
✔✔what is the value for the amount of O2 in the blood - ✔✔3.0 mls O2/ L blood
✔✔how much O2 do we consume each minute - ✔✔250 mls O2/ min
✔✔what is the carrying capacity of hemglobin - ✔✔1.34 mls of O2
AND SOLUTIONS GRADED A+ TIP
✔✔rate of diffusion of a gas is proportional to what and inversely proportional to what -
✔✔proportional to area of membrane
inversely to thickness
✔✔what is Fick's law of diffusion for the lung - ✔✔Dl x deltaP
Dl = diffusion capacity of lung for a gas (includes surface area, thickness, solubility, and
weight)
deltaP = pressure gradient
✔✔how do we measure Dl in the clinic - ✔✔use CO, diffusion limited
= V. / deltaP
✔✔where is most of the surface area of the lungs located - ✔✔alveoli air spaces
bc surface area is large and walls are thin
✔✔what governs the movement of gases across the pulmonary membrane - ✔✔Fick's
Law
✔✔perfusion limited - ✔✔gas is limited by pulmonary blood flow
reaches equil. when leaves pulmonary capillaries, so very quickly
example: N2O (nitrous oxide)
✔✔diffusion limited - ✔✔gas is limited by properties of the blood-gas barrier or the gas
itself
never reaches equilibrium
when Dl is low
example: CO, carbon monoxide
✔✔how to fix perfusion limited - ✔✔increase number of RBCs/ increase blood flow
✔✔is oxygen perfusion or diffusion limited - ✔✔perfusion
, depends on blood flow
reaches equilibrium when 1/3 way through capillary bed
✔✔what is the capillary reserve time (CRT) - ✔✔the portion of the erythrocyte transit
time in which no further diffusion of oxygen occurs
✔✔when does diffusion limitation of oxygen happen - ✔✔when Dl is reduced in disease
with exercise, bc RBC time in pulmonary capillary is reduced
✔✔what affects the Dl - ✔✔changes in Hb content
rate at which O2 combines with Hgb
✔✔what diseases decrease Dl - ✔✔pulmonary fibrosis (thicker barrier, less SA)
loss of functional lung tissue (tumor) (less SA)
emphysema (less SA)
anemia (less Hb content)
pulmonary edema (thicker barrier)
✔✔is the Dl of CO2 greater or less than that of O2 - ✔✔greater (5x)
✔✔is CO2 usually perfusion or diffusion limited - ✔✔perfusion
✔✔is oxygen diffusion limited before or after CO2 - ✔✔before
✔✔what is the formula for the total amount of O2 in the blood - ✔✔dissolved O2 +
HbO2
usually around 20 mls O mls of blood
✔✔what is the value for the solubility of O2 (constant) - ✔✔0.003 mls O2 / mm Hg / 100
mls blood
✔✔what is the value for the amount of O2 in the blood - ✔✔3.0 mls O2/ L blood
✔✔how much O2 do we consume each minute - ✔✔250 mls O2/ min
✔✔what is the carrying capacity of hemglobin - ✔✔1.34 mls of O2
