pulmonary diffusion

Question 1

describe henry’s law for equilibrium gas solubility

Answer 1

when a liquid and gas phase are in equilibrium at a given temperature, the concentration of gas in solution is directly proportional to the partial pressure of the gas

Question 2

describe fink’s law for diffusion of gases

Answer 2

it describes the rate of movement of gas between two compartments containing gases of differing partial pressures

Question 3

what is the aprox pressure of oxygen in dry inspired air?

Answer 3

160 mmHg

Question 4

what is the aprox pressure of oxygen wet tracheal air?

Answer 4

150 mmHg

Question 5

what is the aprox pressure of oxygen in steady state venous blood?

Answer 5

40 mmHg

Question 6

what is the aprox pressure of CO2 in steady state venous blood?

Answer 6

46 mmHg

Question 7

what is the aprox pressure of oxygen in steady state alveolar air?

Answer 7

100 mmHg

Question 8

what is the aprox pressure of CO2 in steady state alveolar air?

Answer 8

40 mmHg

Question 9

what is the aprox pressure of oxygen in steady state arterial blood?

Answer 9

100 mmHg

Question 10

what is the aprox pressure of CO2 in steady state arterial blood?

Answer 10

40 mmHg

Question 11

does CO2 or O2 have a higher solubility constant?

Answer 11

CO2

Question 12

when is the dry gas fraction used?
when is the concentration used?
when is the partial pressure used?

(regarding gas vs liquid state)

Answer 12

dry gas fraction-only for gases
concentration-only for solution phase
partial pressure-used for both gaseous and liquid phase

Question 13

describe the relationship of flow of gases across a membrane and area of the membrane, difference in partial pressure, and thickness of the membrane

Answer 13

flow of gas is directly proportional to the area of the membrane and the difference in partial pressure
flow of gas is inversely proportional to the thickness of the membrane

Question 14

relate the diffusion coefficient of a gas with its solubility and its molecular weight

Answer 14

diffusion coefficient is directly proportional to the solubility
and inversely proportional to the square root of molecular weight

Question 15

if a patient develops a diffusion impairment, will they develop hypoxemia or arterial hypercapnia first?

Answer 15

they will develope hypoxemia first because the diffusion constant for O2 is much lower than that of CO2

Question 16

what is the equation for transit time?

Answer 16

t= V/Q

Question 17

is the transfer for the following gases perfusion or diffusion limited?
N2O
O2
CO

Answer 17

N2O- perfusion limited
O2-perfusion limited
CO-diffusion limited

Question 18

what substance prevents CO from reaching equilibrium of partial pressures between alveolar gas and capillary plasma?

Answer 18

hemoglobin

hemoglobin affinity for CO is VERY high

Question 19

if CO2 is so much more diffusible than O2, why doesn’t it reach equilibrium fast?

Answer 19

due to its chemical reaction in the blood (converting to bicarbonate) which slows down the rate of equilibrium

Question 20

when would exercise induced hpoxemia occur?

Answer 20

in a person with a diffusion problem

Question 20

when would exercise induced hpoxemia occur?

Answer 20

in a person with a diffusion problem

Question 21

why is CO used rather than O2 to determine the diffusion capacity of the lungs?

Answer 21

because the binding of CO to hemoglobin maintains a virtually zero Pco in the pulmonary capillaries thus maintaining the partial pressure gradient between alveoli and capillaries

Question 21

why is CO used rather than O2 to determine the diffusion capacity of the lungs?

Answer 21

because the binding of CO to hemoglobin maintains a virtually zero Pco in the pulmonary capillaries thus maintaining the partial pressure gradient between alveoli and capillaries

Question 22

what is the conversion of the D(L)O2 to D(L)CO?

Answer 22

DLo2=1.23DLco?

Question 22

what is the conversion of the D(L)O2 to D(L)CO?

Answer 22

DLo2=1.23DLco?

Question 23

when supine compared to upright, which position will have a greater diffusion constant of CO? why?

Answer 23

supine will because there is distention of the pulmonary vasculature (due to increased pulmonary blood volume) which increases the area available for diffusion

Question 23

when supine compared to upright, which position will have a greater diffusion constant of CO? why?

Answer 23

supine will because there is distention of the pulmonary vasculature (due to increased pulmonary blood volume) which increases the area available for diffusion

Question 24

does exercise increase or decrease diffusion constant for CO? why?

Answer 24

increases it because there is recruitment of capillaries and increased distention of pulmonary vasculature

Question 24

does exercise increase or decrease diffusion constant for CO? why?

Answer 24

increases it because there is recruitment of capillaries and increased distention of pulmonary vasculature

Question 25

would pulmonary diseases increase or decrease diffusion constant? why?

Answer 25

decrease it because there is decrease pulmonary surface area

Question 26

give some examples of how diffusion constant could be decreased due to increased diffusion distance

Answer 26

• Thickened alveolar membrane (like pulmonary fibrosis)
• Accumulation of fluids (pulmonary edema)
• Pulmonary inflammatory or allergic responses

Question 27

the difference in the effect of diffusional barriers on O2 and CO2 equilibration is due to what?

Answer 27

the high solubility of CO2 in tissues and fluids