B4.036 - Gas Exchange and Transport Flashcards
what is the equation for pressure of a gas
P = nTR/V
what do you need to calculated partial pressure
Total pressure and concentration of a gas species
what is FO2
fraction of O2
how do you calculate PIO2
PIO2 = (760-47) * .21
in kansas city what should the sum of partial pressures of all gases add up to
PB aka 747
how do you change partial pressure of a gas
changing the concentration or the total pressure
what is the physical solution of gas in the liquid
the fraction of gas molecules that enters the liquid and does not undergo any chemical combination
does O2 combined with Hb contribute to PO2?
No, any gas molecule that combines with a substance in the liquid does not contribute to the partial pressure of the gas
in order for partial pressures of gas not to fall what must occur
the gas molecules must be replaced by additional molecules entering the liquid from the gas phase
what does hyperventilation do
high PAO2, low PACO2
what does hypoventilation do
low PAO2, high PACO2
what is the alveolar gas
the result of a balance between the rate of delivery and the rate of removal of each individual gas
describe air in the conduction system and respiration system at the end of expiration
the alveoli and airways are filled with alveolar air, volume of air in the lungs at that time is FRC
how much air remains in dead space during inspiration
1/3
what does this graph represent
gas composition pattern during breathing
during expiration PCO2 initially is low because of O2 left in the dead space, then once the air from the alveoli is exhaled you see a rise in PCO2. The opposite is true for PO2 for the same reason
how do you calculate VD/VE
VD/VE = (FACO2 - FECO2)/FACO2
what key differences does this graph demonstrate
- in the physiologic range, the blood CO2 content is about 2x the blood O2 content
- the curve for CO2 is fairly linear (changes in CO2 yeild proportionate changes in blood CO2 over a wide range of PCO2)
- teh non linearity of the ODC means the changes in O2 content produced by a given change in PO2 will depend on the initial PO2 level
- the CO2 curve is much steeper, note the v-a difference and its implications on PCO2 and PO2
what is the alveolar gas equation
PAO2 = PIO2 - (PaCO2 x 1.2)
what is the alveolar gas equation used for
PAO2 = PIO2 - (PaCO2 x 1.2)
to compare the measured arterial blood PO2 and the calculated one. In the normal lung PaO2 should be only 5-10 mmHg lower than calculated PAO2
what is normal inspired PIO2?
147 (PB in kansas city)
what is inspired PCO2?
always 0
why is alveolar PO2 lower than PIO2?
because the second it hits the alveoli gas exchange happens
goes from 147-100
what is normal aveolar PCO2?
40
how do you get the PIO2
(760-47) * .21
760 - atmospheric P
47 - subract H20 Pressure
.21 - fraction of inhaled air that is PO2
= 147
what is the difference between arterial and venous PCO2 and PO2
PO2 - 100 in art, 40 in veins
PCO2 - 40 in art, 46 in veins
what is anatomical dead space
any air that doesnt make it to the alveoli, doest undergo gas exchange
what is physiological dead space
areas of alveoli that have a pathology preventing gas exchange
how do you calculate VD/VE
VD/VE = (FACO2-FECO2)/FACO2
Alveolar CO2 should be 40, so if you exhale and the Fraction of that is 30 (it will always be less because of the dilution with dead space air that has no CO2) subtract those and put it over the 40 that gives you the fraction of dead space
give an example with numbers of how the VD could increase (use VD/VE equation)
FACO2 - 40
FECO2 - 20 (theres more dead space aka more dilution)
VD/VE = (40-20)/40 = .5
what does this graph represent
effect of hyperventilation and hypoventilation on VA and PACO2
how do you calculate PAO2
PAO2 = PIO2 - PACO2
what is the alveolar gas equation and how do you use it
PAO2 = PIO2 - (PaCO2 * 1.2)
PIO2 - usually 147, comes from (atmospheric - H20) *FO2
PaCO2 - usually 40
1.2 - used to correct for the fact that O2 : CO2 isnt an exactly 1:1 ratio
its used to look at ventilation in the airways
what is PAO2 if PIO2 is 147
and theres a 25% increase in ventilation
111
what does it mean if calculated PAO2 is off from PaO2 by more than 5-10 mmHg?
Something is wrong with ventilation
what is the equation for diffusion across a membrane
M = (C1-C2) * A * D/ X
what is the main driver of diffusion across a membrane
concentration gradient
what is the equation for diffusion of gases in the lung
DLx = Vx / (PA - Pa) x
DLx - diffusion capacity
what gas is perfusion limited and what does that mean
N2O
It does not combine readily with anything in the blood, this means its limited unless theres a constant supply of new blood with no N2O
what are the characteristics of CO as far as diffusion capacity
has a much higher diffusion capacity because its able to combine readily with Hb, this means that when its bound to a protien it does not contribute to the partial pressure so more can diffuse across
what relationship is being demonstrated here
N2O is perfusion limited, concentration goes up really quickly because it does not readily combine with anything in the blood
CO - is diffusion limited because it does combine readily with Hb
how long does it take for PO2 to go from 40 -100 when it reaches the alveoli
.25 seconds
how long does it take for CO2 to diffuse out of blood into alveoli
.25 s
why is it that the diffusion time of CO2 and O2 are roughly the same even though the gradient for O2 is so much higher than CO2?
the diffusion capacity of CO2 is a lot higher than O2
what lung properties can change the surface area available for diffusion
pulmonary edema
Fibrosis
inflammation
what effect does inflammation have on diffusion
increased thickness of membrane leading to lower diffusion capacity of O2
what does the red B line represent in these graphs
mild/moderate reduction in DLO2
what does the blue line C represent in these graphs
severe reduction in DLO2, low PaO2 beacuse of this
Compensatory hyperventilation may lower PaCO2
desribe the use of CO for finding the diffusion capacity for lung O2
CO diffuses accross so readily that if theres any diffusion limitation it will be easy to tell
DLCO = VCO/PACO
how do you calculated O2 saturation of Hb (%)
O2 sat of Hb = (HbO2/Hb*1.34) X 100
how do you calculate blood O2 content
Blood O2 content = (dissolved portion) + (amount bound to Hb)
Blood O2 content = (.003 x PO2) + ([Hb] x 1.34 x %O2 sat)
what does this curve domonstrate
Its the O2 dissociation curve of Hb (ODC)
Arterial PO2 at 100% saturation is about 100
the venous PO2 (40) still has a Hb% saturation of about 75%
what kinds of things can cause a right shift of the ODC
High PCO2
Low pH
High Temperature
High 2,3, DPG
excersizing muscle
what kinds of conditions can cause a left shift in the ODC
Low PCO2
High pH
Low temperature
low 2,3, DPG
what does this graph demonstrate
what is a
what is the blue line
what is v
this is a graph demostrting blood O2 content (dissolved + bound)
a - arterial
v - veins
blue line - low Hb
what kind of pathologies can account for the blue line
anemia
what does this graph demonstrate
how does it change during exercise?
the metabolism of O2 in the body
the difference between a and v is how much oxygen is used by the body
the a-v ration can change so that the body is extracting more oxygen making the veinous O2 lower than normal
where is bicarb produced more in the RBC or the plasma? Why?
RBC
the enzyme Carbonic anhydrase (CA) catalyzes the reaction
where does the bicarb made by the RBC go and why
goes to the plasma because of the Cl- exchange, bicarb diffuses out easily but H+ does not so Cl - goes in in exchange
what is the haldane effect
Deoxygenated Hb is a better carrier for CO2
When Hb is not bound to O2 its more likely to pick up Hydrogen ions, this drives the equation to the right producing more HCO3-
what does this graph demonstrate
why are there 2 lines and why are they straight
haldane effect
Increase in O2 means a decrease in blood CO2 concentration
CO2 and Hb has a linear relationship
what does this graph demonstrate
You can see the differences in a-v between CO2 and O2
PO2 drops much from arterial to veinous than PCO2
