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56 Cards in this Set
- Front
- Back
what does hte O2/Hb disassociation curve do to change affinity
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shift left
shift right |
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where does gas exchange occur
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Lungs: O2 from alv gas into pulm capillary. CO2 from pulm capillary into alv gas
Tissue: O2 from blood to cells, CO2 from tissues into pulm blood |
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Fick does what?
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diffusion
V = D A P/X *the volume of gas transferred is equal to the diffusion coef times area times pressure/thickness |
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so diffusion is proportional to...
inversely proportional to... |
Directly: Pressure, SA, Dif coef (vaires with gas)
Inverse: membrance thickness |
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when does membrane thickness really affect diffusion
what about SA |
not normally an issue except in fibrosis when thickness increases
** V= D A P/X SA increased with exercise, decreased with emphysema |
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what does emphysema do to diffusion, how
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it decreased it by decreaseing SA
V = D A P/X |
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what is the friving force for diffusion
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PRESSURE GRADIENT
V = D A P/X FICK |
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what is the diffusion coeffecient of a gas. what determines it
what gas has a higher D |
its the ability of it to diffuse. MW and solubility
changes with gasses CO2 is WAY more soluble thatn O2 so CO2 has a higher diffusion coef |
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for a given P what diffeses faster CO2 or O2, why
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CO2. it has a higher D (MW and solubility, CO2 solubility > O2 solubility)
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what is lung diffusing capacity
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A single term that combines these:
1. D (MW/SOlubility) 2. SA 3. THickness 4. Time required for gas & protein to combine **measured with CO |
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why do we use CO to measure the lung diffusing capacity
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its limited only by diffusion in the lungs
**Dl is proportional to the rate of disappearance of CO from a mixed gas while the pt breathes this gas in Dl: SA, Dif, Thick, Time to combine with protein |
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how does Dl change in emphysema
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decreases
Alv destruction decreases SA Dl: SA, Thick, Dif, Time to combine |
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what does Dl do in fibrosis or pulm edem
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decrease
**increased thickness, this makes diffusion limited transport. The membranes are SO thick there is not enough time to get all of the O2 transported Dl: thickness, SA, diffusion, time to combine with protein |
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how does Dl change with anemia
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decreased Dl
((decreased Hg so increased time to combine) Dl: SA, D, thick, time to combine |
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how does Dl change with exercise
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increases
Increased SA for gas exchange **Dl: SA, Diffusion, Thick, time to combine |
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how is Dl measured
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with CO, its diffusion limited
*CO moves from alv to blood, as soon as the CO enters blood it binds to Hg. we know that when the CO is bound it no longer exerts a partial pressure. In this manner the PCO is always kept low and there is a constant driving force to move CO into the blood. diffusion limited *contrast to the process of N20, this gas is always dissolved so the partial pressures (only contributed by dissolved blood) equilibrate quickly and transport is perfusion limited |
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where is CO solubility low, high
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low: capillary membrane
high: blood Dl= diffusion/delta P |
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why is it a good idea to know the Dl
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tells us about diffusion across the alv/pulm cap
1. ability of gas to move 2. Dx obstructive/restrictive disease 3. general assessment of how healthy |
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what is the method employed to measure Dl
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single breath method
Pt breathes a mixture of gases, incldugin a small amt of CO, the Dl is proportional to the disappearance of CO **Pt exhales and then inhales max (RV to TLC is breathed of the mixed gas) **wait to allow diffusion to occur **breath out first part of air (conducting), measure the second part of breath (respiratory zone) |
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what is the formula for Dl
what is a normal value |
DL = VCO/Delta PCO
OR Vent rate of CO/PACO 20-30 |
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what is the diffision capacity for CO if PCO=0.1 and 0.25 ml CO was taken up
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0.25 x 6 / 0.1
**multiply 0.25 by 6 to get the diffusion for a full minute (we held breath for 10 sec) |
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what decreases Dl
increases |
1. increased thickness (fibrosis)
2. decrease SA (emphysema) 3. loss of lung tissue (pulm resection) 4. anemia, increased time for gas combining with protein (?????) Dl is increased by exercise which increases the SA |
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Is Dl the same for everyone
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nope:
large young men have the highest Dl age decreased Dl size increased Dl males have larger Dl |
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where are gasses found in soln
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the blood
**alv air has one gas and is expressed at a partial pressure **blood has a muxture (dissolved, modified, bound) |
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how are gasses carried in the blood
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blood, soln of gasses
gasses are: 1. bound: ex O2/ HG 2. Dissolved: 3. Modified: CO2 --> HCO3 |
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what gas in the blood is never bound or modified, what is it
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nitrogen, dissolved
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where is CO2 converted to HCO3
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RBC
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what is henrys law
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C= P x Solubility
For Dissolved gasses AMt of gas in a liquid is equal to the partial pressure of the gas times its solubility |
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what 3 circumstances give diffusion limited transport, what gas is diffusion limited
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1. exercise
2. fibrosis 3. emphysema CO **diffusion limited, pressure differnece is maintained |
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where is Henrys Law applicable
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blood, with dissolved gas
**only dissolved gas contributes to partial pressure of a gas Amt of gas= PP x Solubility **N2 is the ONLY gas that is found ONLY in its dissolved form (used to measure respiratory Fx) |
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what are the levels of CO2 and O2 in:
dry inspired air humidified air Alv air Blood Mixed venous blood systemic arterial blood |
Dry Inspired: O2 160, CO2 0
Humidified Air: O2 150, CO2 0 Alv Air: O2 100, CO2 40 Venous blood: O2 40, CO2 46 Arterial Blood: O2 100, 40 |
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what is the CO2/O2 of blood that entert the lung, what about when it leaves
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Venous (enter): O2 40, CO2 46
Arterial (exit): O2 100, CO2 40 **The arterial and alveolar levels will equilibrate |
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the levels of CO2/O2 in what two areas equilibrate
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Alv Air
Arterial Blood CO2 40 O2 100 |
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what happens to air as it is inhaled
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dry: O2 160
humidified: O2 150 Alv: O2 100 **CO2 is 0 until the alv where it is 40 |
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what is daltons law of partial pressures
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the pp of a gas in a mixture of gasses is the pressure that gas would exert if it were the only gas present
partial Pressure = total pressure x fractional gas [conc] Px- pp of gas Pb- barometric pressure (constant) F- fraction of gas (in ATM wont change) |
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calc the pp of O2 in dry inspired air
ATM: 760 fractional is 21% |
Pp=total P x fractional gas conc
PP= 760 x 0.21 pp=160mmHg **Daltons law |
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what is the pp of humidified tracheal air
37* C PP H20= 47 |
PO2 = 760-47 x 0.21
PO2=150 Daltons Law |
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the amt of gas dissolved in blood is proportional to what
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the partial pressure of the gas
Dissolved [O2] = PO2 X solubility of O2 in blood |
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in perfusion limited gas exchange what will increase diffusion
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increased BF
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what is the difference in equliibration in perfusion and diffusion gas exchange
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1. Perfusion: equilibrates early along the pulm cap, pp of alv gas = pp of gas in blood
2. Diffusion: equilibration does NOT occur by the time blood passes through the pulm cap. Usually the PP in the alv = alv blood but not in diffusion limited cases |
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what is daltons law
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PARTIAL PRESSURE
*PP of gas = barometric P x fraction of gas (O2 is 0.21) |
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how does daltons law change for humidified air
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PP= Baromet - 47 x 0.21
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what is the pp of O2, and what is the pp of humidified O2
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PP= 760 x .21
PP humidified= 760-47 x .21 |
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what is the fractional concentration of O2 in air
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0.21
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whats the ppO2 of dry inspired air?
humidified? alveolar? **what formula allows us to calc thses |
dry: 160
humidified: 150 alveolar: 100 **Daltons Law PO2 = Pbar x 0.21 PO2= Pbar - 47 x 0.21 |
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what is the PaO2 and PaCO2 of mixed venous blood? what is the PaO2 and PaCO2 after this blood leaves the alv
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O2 40
CO2 46 After Gas exchange PaO2 100 PaCO2 40 |
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why is the PaO2/CO2 the same as PAO2/CO2 (arteriolar, not venous)
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equilibration of diffusion
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what are the 2 ways gas exchange can be limited
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1. diffusion: equilibration wont occur, gases always have driving force for diffusion
2. perfusion: pressures equalize, the only way to increase gas transport is by increaseing BF |
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what kinds of gases exert a pp
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the kind that are directly disolved in the blood
**bound gases wont exert a pp |
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is O2 usually diffusion or diffusion limited
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perfusion
*regulated bt BF |
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what would cause O2 transport to be diffusion limited rather than perfusion limited
What gas is diffusion limited, what gad is perfusion limited |
usually perfusion
**diffusion limited w/ fibrosis -decreased time for diffusion to take place -Dl is low -PAO2 is low **CO is diffusion limited (no equilibration) **N2O is perfusion limited (wquilibration) |
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what would decreased time for gas transport do to diffusion/perfusion limited gas exchange
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difusion limited
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if Dl is low how is diffusion/erfusion limited gas exchange affected
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diffision limited rather than perfusion
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if PAO2 is low will gas transport be diffsion or perfusion limited
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diffusion
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how do we know normally gas exchange is perfusion limited
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the PaO2 and PAO2 equilibrate at the first 1/3 of the capillary and then just float down the rest of teh blood river without transort
**only an increase on BF will increase transport |
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in diffusion limited gas exchange what happens to pp gradient
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maintained throughout the length of the vessel. anything that causes diffusion to decrease will maintain the dradient and become diffusion limited
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