Lecture 38: Gas Transport: Oxygen and Carbon Dioxide Transport Flashcards
A woman has low hemoglobin because she has a heavy period, what is expected to decrease? A.Arterial PaO2 B: Arterial Hb saturation C. Dissolved O2 D. Total O2 content
D= that is the only thing that changes with anemia
what are the two states in which oxygen is transported ?
1- In a dissolved state in plasma:
solubility of oxygen is 0.003 ml O2 per dl/plasma
Dissolved O2=PO2* solubility
100X.003= 0.3 ml/dl
O2 consumption is over 250 ml and pumping 83 L of blood per min is not realistic.
2- Bound form in plasma to hemoglobin in RBCs.
binding reversibly to oxygen
Calculate the max amount of oxygen that can be bound to hemoglobin.
1 gm of hemoglobin can bind 1.36 ml O2
if blood has 15g
1.36*15= 20.4ml O2 is they carrying
Calculate the max amount of oxygen that can be bound to hemoglobin, carrying capacity…
1 gm of hemoglobin can bind 1.36 ml O2
if blood has 15g
1.36*15= 20.4ml O2 is they carrying capacity
What is the equation for saturation of oxygen?
SO2= HbO2 content/ HbO2 capacity *100
content= actual capacity= what it can
hemoglobin needs to be in ____ state to bind to oxygen
relaxed
what is the shape of the saturation curve ?
sigmoidal
slide 13
As you increase the PO2 of oxygen Hb saturation _____ and O2 content _____
increases, increases
the graph then plateaus at 100ml… Once all Hb are filled the hb cannot bind oxygens
What occurs at the plateu phase of the curve? where does it occur? what phase?
at Alveolar PO2 you can get over 90% saturation… this occurs at the loading phase in the lungs…
( same graphs) What occurs at the steep portion of the curve ( box)? where does it occur? what phase is it?
small changes of partial pressure O2 cause large changes in HB saturation and content. this usually occurs in the tissues….
this phase is considered the unloading phase
what does P50 tell you?
when 50% of hemoglobin binding sites are full
look at pic
ex look at y axis get half then track down to x axis
what occurs if you have an increase in P50?
O2 dissociation curve shifts right. it means that hemoglobin has a lower binding affinity for oxygen.. theres a lot more oxygen
If you have decreased P50 what occurs?
Shift left….you have smaller P50, the hemoglobin has a higher affinity
what 4 things increase P50?
aka shifts right/ easier unloading lower affinity
- increase in temperature
- decrease PH
- increase CO2
- high 2,3 bisphosphoglycerate
what is the Bohr effect?
when there is an increase in PCO2 increase in acid then it shifts right, less affinity for oxygen
what is the affect of alkalinity in the blood?
then the graph shifts left causing more affinity to oxygen
also low temperature and low CO2 will do this
what occurs in the O2 saturation curve if you have anemia? what causes the symptoms
Saturation will not fall because all of the available O2 binding sites are full, (SaO2 is normal)
PaO2 is normal
Saturation is normal.
less binding sites exist in total so the O2 content is decreased, hypoxia causes their symptoms…
Its like having less hemoglobin molecules available to bind the oxygens.
if me and someone else have 100% oxygen saturation all the sites are filled even if I have 2 hemoglobin and them 1
What occurs if you have polycythemia? what happens to viscosity ?
- you have increased RBCs, and carrying capacity but you have no change in affinity, only more binding sites for O2.
- increased blood viscosity
- bleed them is better
what occurs in CO poisoning? to affinity? graph shift where? P50 increases or decreases? oxygen content? phenotype of blood? what are the physical symptoms?
- Increased affinity for CO
- shifts left from normal Oxygen binding
- decreases P50 and oxygen has a hard time unbinding to get released to the tissues
arterial pressure and dissolved oxygen the same
oxygen content decreases
CHERRY RED
brain affected first, slow rxn time, blurred vision, coma..
how do you treat a carbon monoxide poisoning?
remove person from the source, add 100% oxyge, mix with 5% CO2 to improve alveolar ventilation.
Review: what is bulk flow?
Conducting system: many gas molecules moves from trachea to alveoli…
driving pressure is the pressure gradient
Review: what is diffusion?
that’s how gas moves from alveoli to blood or from blood to tissues
what does diffusion depend on?
pressure gradient, decreased thickness of membrane, increased surface area, diffusion coefficient
what are the barriers that the Oxygen and CO2 have to pass in the respiratory membrane to go from the alveolus to the RBC?
alveolar epithelium> Fused basement membranes of endothelial cells> capillary endothelium
( squamous epithelial cell nucleus)
AFC
what are the layers that oxygen and CO2 need to trespass to reach RBC? “diffusion barrier”
alveolar fluid—type 1 cell—-interstitium—- endothelial cell— plasma— RBC
atiep
what is transit time?
Getting oxygen from alveoli to blood.
the time required for a RBC to move in the alveolar capillary is 0.75 secs at rest. this is the time the blood or RBC has to equilibrate with alveolar gas tension.
what occurs to transit time with exercise?
it is decreased due to rapid blood flow
N2O; what is it for what is the limitation? How long does it take to equilibrate? At equilibration partial pressure= what?
Dental anesthetic
does not bind to Hb
it takes 0.10 seconds to equilibrate.
at equilibration partial pressure gradient=0 no more gas can diffuse unless there is new blood flow= perfusion limited
O2 How long does it take to equilibrate?
0.25 seconds to equilibrate
CO what is the limitation?
never equilibrates, gas continues diffusing and hemoglobin never saturates.
rate of diffusion though the capillary is slower..
it takes >0.75 seconds for Hb to be fully saturated.
- constant partial pressure gradient PACO, PaCO ( pulmonary capillaries,
DIFFUSION LIMITED GAS
under physiological conditions oxygen is a _____ limited gas?
perfusion limited gas
What conditions are oxygen diffusion limited?
Pulmonary edema, pulmonary fibrosis CO2 retention ( cannot blow off all CO2)
( look at graphs 40 up)
- increases barrier thickness reducing the rate of diffusion.
what does perfusion limited mean?
there is equilibration of gasses between alveolar and pulmonary capillary
what does diffusion limited mean?
there is no equilibration of gas between alveolar and pulmonary capillary.
What does diffusion limited mean?
there is no equilibration of gas between alveolar and pulmonary capillary
what do you use to measure diffusion capacity? AKA DL?
single breath test with carbon monoxide.
why is carbon monoxide used to measure diffusion capacity?
- PCO is diffusion limited only
- none in venous blood
- its avidity to binding Hb maintains PaCO near zero
how is DL assessed?
breath out residual volume
take the max inspiration with 0.3 CO
hold breath 10s
breath out and measure CO and He
Measure the diff between the concentration of He in inspired and expired air
Measure the difference between the concentration of CO in inspired and expired air (corrected for the He dilution)
Use equation DL=Vco/PACO
normal is 20-30 ml CO
what occurs to DL with pulmonary fibrosis, edema, or loss of alveolar membrane emphysema?
it is decreased less than 20 ml CO
a girl breaths fast and is anxious. she is hyperventilating. She had decreased P50 on her O2 hemoglobin dissociation curve. what is most likely this due to? A acidosis B hypocapnia C decreased PCO2 levels D decreased PaO2 levels E increased levels of 2,3 bpg
decreased PCO2 levels
what is the most predominant form of transporting CO2?
1- bicarbonate 60%
2: carbamino compounds 30%
3. dissolved CO2= 8-10%
minor carbonic acid and carbonate
CO2 has ___ solubility in water than O2
greater
What occurs when there is an increase in PCO2 in tissues?
- it drives CO2 into the blood
- small portion dissolves
- most of it diffuses into RBC
what is PCO2 converted into in the RBC? and by what enzyme?
into HCO3-
by carbonic anhydrase
What occurs to the majority of HCO3- formed in RBC?
it moves out of the cell
what is the purpose of CL- in RBC?
moves in to maintain the electrical neutrality, does a chloride shift
What occurs to H+ in RBC?
it remains in the cell and combines to O2m to make Hb-O2
HHb to be sent to tissue
CO2 binds with free amine groups NH2
forms carbamino ions Hb-NHCOO- and also makes HBH and HBO2 for tissue (20-30%)
what is the Haldane effect.
the inverse relationship between CO2 PO2 and CO2
For an increased os PO2 it shifts right
SEE PIC
Haldane effect allows more CO2 to load in tissues, and unload more CO2 in lungs.
For any given partial pressure, you can load _____ CO2 than O2
more
small changes affect CO2 more
GRAPH
