physical principles of gas exchange Flashcards
air is composed of
79% nitrogen, 21% oxygen
total pressure of air mixture -
760 mmHg
1 atm
760
nitrogen partial pressure is
79% of 760= 600
oxygen partial pressure is
21% of 760 = 160
henrys law
the solubility of a gas in a liquid depends on temp, the nature of the solvent, and the nature of the gas.
the colder, the ___ gas is dissolved
more
gas is ____ soluble at high temps
less
gas is ___ soluble at low temps
more
net diffusion of gases is determined by
differences in partial pressures
if pp of gas in alveoli > blood,
gas moves into blood
if pp of gas in blood > alveoli,
gas moves into alveoli
vapor pressure is ___ mmHg when gas mixture is fully humidified at 37degrees
47
factors that affect gas diffusion rates
pressure, gas solubility, distance, molecular weight, temp
diffusion coefficient is dependent on
solubility and molecular weight
if a gas is highly soluble, it has a ___ diffusion coefficient
high. direct relationship
if a gas is less soluble, it has a ___ diffusion coefficient
low
heavier gases move
more slowly
D is ____ to the square root of the gas’ molecular weight
inversely proportional
rate of gas movement into tissues is limited by diffusion rate of gas through
tissue water
alveolar air is ___ replaced by atmospheric air during each breath
partially. protects you and acts as a buffer from sudden changes.
each breath replaces ___ of FRC
1/7th
normal alveolar ventilation removes 1/2 of gas in ___ seconds
17
half normal ventilation removes 1/2 of gas in __ seconds
34
twice normal removes half of gas in
8 seconds
normal alveolar PO2 is ___ mmHg
100
how much o2 do you need to consume at rest a minute
250ml
normal alveolar PCO2 Is ___ mmHg
40
alveolar PCO2 ___ in proportion to CO2 excretion
increases
PCO2 ___ in inverse to alveolar ventilation
decreases
alveolar air is expired at
end of exhalation
overall thickness @ ___ mm
.6
total surface area
70 sq meteres
RBC squeeze through __ mm diameter capillaries
5
ficks law tells you about
diffusion of gas thru a tissue membrane
if the resp membrane is thicker, the rate of diffusion will be ____
slower
increasing thickness by ___ times interferes significantly with normal resp exchange
2-3
decreasing surface area ____ gas exchange
decreases
decreasing by ___ normal impedes gas exchange significantly
1/4
emphysema
dissolution of many alveolar walls to collapse alveoli into larger chambers. (surface area decreased as much as 5-fold)
oxygen diffusion compared to nitrogen
o2 is twice as fast
CO2 diffusion compared to oxygen
co2 is 20 times faster
CO2 diffusion compared to oxygen
co2 is 20 times faster
diffusing capacity definition
the volume of a gas that will diffuse through the resp membrane each minute for a pressure diff of 1 mmHg
the pressure difference multiplied by the diffusing capacity =
the total quantity of O2
diffusing across the membrane per minute
with exercise diffusing capacity increases three fold to max at
65
during exercise the lung is in zone
3
diffusing capacity of CO2 at rest
400
diffusing capacity of CO2 during exercise
1200
the more soluble in water,
the faster diffusion
which gas is the least soluble
nitrogen
pressure difference affects gas diffusion how
difference in partial pressures of gas in alveoli and pulmonary blood
CO2 is highly
soluble. diffuses rapidly thru resp membrane
if v/q ratio is either zero or infinity
there is no exchange of gases
if ventilation is present but no perfusion then v/q =
infinity
if ventilation = zero but perfusion is present, the v/q is
zero (complete airway obstruction) like mucus plug
if v/q is zero, alveolar concentration will equal
venous blood. air in alveoli reaches equilibrium with deoxygenated blood returning to lungs in pulm arteries
in normal deoxygenated blood the PO2 is
40
in normal deoxygenated blood the PCO2 is
45
when v/q equals infinity, the alveolar air..
becomes equal with humidified inspired air. no loss of oxygen into blood. no gain of co2 from blood
when v/q equals infinity, P02 is
150
when v/q equals infinity, pco@
0
normal alveolar po2
100
normal alveolar pco2
40
pulm embolus
infinity
if v/q is below normal
perfusion but no ventilation. blood is being shunted from PA to pulm vein without participating in gas exchange
the greater the shunt, the greater the amount of blood that
fails to be oxygenated in lungs
dead space
vent but no perfusion. ventilation to alveoli is good but blood flow is low
physiologic dead space includes
wasted ventilation, anatomical dead space
v/q ration greater than normal
dead space. PE and what else?
the more rapidly o2 is absorbed, the ____ its concentration in the alveoli becomes,
lower
the more rapidly new o2 is breathed into the alveoli from the atmosphere, the ___ the concentration becomes
higher
the greater the physiologic shunt, the greater the
amount of blood that fails to be oxygenated as it passes thru the lungs
ficks law
(a x pp x d) / thickness
diffusion coefficient depends on
solubility + .. and weight -
normal CO2 production at rest
200ml/min
PO2 100 when leaving pulm but LA blood is ___ because of?
95 because of bronchial circulation blood.
why is pp of o2 in upper airway 150
water vapor.. 713 + 47
frc is roughly
2500ml
___ ml air per breah
330
during exercise, dead space is ___
reduced
