pulmonary diffusion Flashcards
describe henry’s law for equilibrium gas solubility
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
describe fink’s law for diffusion of gases
it describes the rate of movement of gas between two compartments containing gases of differing partial pressures
what is the aprox pressure of oxygen in dry inspired air?
160 mmHg
what is the aprox pressure of oxygen wet tracheal air?
150 mmHg
what is the aprox pressure of oxygen in steady state venous blood?
40 mmHg
what is the aprox pressure of CO2 in steady state venous blood?
46 mmHg
what is the aprox pressure of oxygen in steady state alveolar air?
100 mmHg
what is the aprox pressure of CO2 in steady state alveolar air?
40 mmHg
what is the aprox pressure of oxygen in steady state arterial blood?
100 mmHg
what is the aprox pressure of CO2 in steady state arterial blood?
40 mmHg
does CO2 or O2 have a higher solubility constant?
CO2
when is the dry gas fraction used?
when is the concentration used?
when is the partial pressure used?
(regarding gas vs liquid state)
dry gas fraction-only for gases
concentration-only for solution phase
partial pressure-used for both gaseous and liquid phase
describe the relationship of flow of gases across a membrane and area of the membrane, difference in partial pressure, and thickness of the membrane
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
relate the diffusion coefficient of a gas with its solubility and its molecular weight
diffusion coefficient is directly proportional to the solubility
and inversely proportional to the square root of molecular weight
if a patient develops a diffusion impairment, will they develop hypoxemia or arterial hypercapnia first?
they will develope hypoxemia first because the diffusion constant for O2 is much lower than that of CO2
what is the equation for transit time?
t= V/Q
is the transfer for the following gases perfusion or diffusion limited?
N2O
O2
CO
N2O- perfusion limited
O2-perfusion limited
CO-diffusion limited
what substance prevents CO from reaching equilibrium of partial pressures between alveolar gas and capillary plasma?
hemoglobin
hemoglobin affinity for CO is VERY high
if CO2 is so much more diffusible than O2, why doesn’t it reach equilibrium fast?
due to its chemical reaction in the blood (converting to bicarbonate) which slows down the rate of equilibrium
when would exercise induced hpoxemia occur?
in a person with a diffusion problem
when would exercise induced hpoxemia occur?
in a person with a diffusion problem
why is CO used rather than O2 to determine the diffusion capacity of the lungs?
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
why is CO used rather than O2 to determine the diffusion capacity of the lungs?
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
what is the conversion of the D(L)O2 to D(L)CO?
DLo2=1.23DLco?
what is the conversion of the D(L)O2 to D(L)CO?
DLo2=1.23DLco?
when supine compared to upright, which position will have a greater diffusion constant of CO? why?
supine will because there is distention of the pulmonary vasculature (due to increased pulmonary blood volume) which increases the area available for diffusion
when supine compared to upright, which position will have a greater diffusion constant of CO? why?
supine will because there is distention of the pulmonary vasculature (due to increased pulmonary blood volume) which increases the area available for diffusion
does exercise increase or decrease diffusion constant for CO? why?
increases it because there is recruitment of capillaries and increased distention of pulmonary vasculature
does exercise increase or decrease diffusion constant for CO? why?
increases it because there is recruitment of capillaries and increased distention of pulmonary vasculature
would pulmonary diseases increase or decrease diffusion constant? why?
decrease it because there is decrease pulmonary surface area
give some examples of how diffusion constant could be decreased due to increased diffusion distance
- Thickened alveolar membrane (like pulmonary fibrosis)
- Accumulation of fluids (pulmonary edema)
- Pulmonary inflammatory or allergic responses
the difference in the effect of diffusional barriers on O2 and CO2 equilibration is due to what?
the high solubility of CO2 in tissues and fluids
