Flashcards in Gas Transport Deck (41):
Solubility of O2= .3 ml O2/dL blood/100 mmHg
-So, if the PaO2 is 100 mmHg, each dL of blood will carry?
.3 ml O2
In order to meet our metabolic demands our hearts would have to?
Pump an impossible amount of blood
When we refer to Pa O2 (the partial pressure of Oxygen in the arterial blood) what form is the oxygen in that we are actually referring to?
Obviously we have found a better solution?
At any PO2 > 60 mmHg, O2 saturation of Hb is at least (%)?
-What does this mean?
-At any PO2 > 60 mmHg, O2 saturation of Hb is at least 85%
20.1 ml O2/dL blood x .85
=17 ml O2/dL blood-Readily supplies us with enough oxygen to meet metabolic demand
Solubility of O2?
.3 ml O2/dL blood/100mmHg
Hb-O2 curve-What does a "Left Shift" represent?
A left shift represents an increase in the affinity of Hb for O2
(right shift is the opposite)
Factors which produce shifts in the Hb-O2 curve?
-CO2 and/or pH
-The Bohr effect
Factors that induce a right shift?
-High CO2 or low pH
-Increased 2,3 DPG
PaO2=95 mmHg and PvO2=40 mmHg
What do these numbers indicate?
These numbers indicate that not all of the oxygen is taken up by the tissue, as indicated by the venous PO2 of 40 mmHg
The O2 saturation of venous blood is about?
75%-->20.1 ml O2/dL blood x .75 = 15.2 ml O2/dL blood
a-v O2 difference
-Why is it important?
-The difference between the arterial O2 content and the venous O2 content
-Represents how much oxygen was USED by the tissue being perfused
a-v O2 difference
-variation from tissue to tissue?
-The a-v O2 difference varies substantially from tissue to tissue
-Adipose tissue removes very little O2 from the blood
-Skeletal muscle removes much more O2
-The reason is because the oxygen utilization by the two tissues is very different
There is a consistent relationship between the amount of O2 consumed and the CO2 produced
-The relationship/ratio is determined by?
The fuel being utilized by the cells
If the cells are using carbohydrates as fuel the ratio is?
there is a 1:1 ratio
-1 CO2 produced for every O2 consumed
If the fuel is fats the ratio is?
7 CO2 : 10 O2 (.7)
Usually, however, there is a mix fuels-ratio?
.8 (8 CO2 : 10 O2)
The Respiratory Quotient (RQ)
-What is it?
-***How is it calculated?***
-The ratio between CO2 produced and the O2 consumed
RQ= (vol. CO2 produced)/(vol. O2 consumed)
So, how much CO2 can dissolve in the plasma?
-Compared to that of oxygen?
CO2 has much greater solubility in water (therefore plasma) than O2
-The solubility of CO2 is 6 mlCO2/ dL blood/ 100 mmHg
Since the PCO2 of the venous blood is 45 mmHg, there is about 2.7 ml CO2 dissolved in each dL of blood
Once again we would need an impossible cardiac output to deal with this volume of CO2 produced every minute
-So, how do we deal with it?
CO2 can combine with plasma proteins or Hb to form carbamino compounds
What ACTUALLY happens when CO2 binds to Hb?
-How much of CO2 is carried this way?
-CO2 actually binds to the amine groups of the chains (not the heme)
-Haldane shift-the presence of O2 on the heme reduces the affinity of the Hb chain for the CO2
-About 7% of the total CO2 is carried this way
What is the main way CO2 is carried through the body?
Most of the CO2 in the blood is carried as bicarbonate (HCO3)
-86% of the total (44 ml of CO2)
Explain this whole reaction
-H2O diffuses across RBC membrane and coupled with CO2-->H2CO3
-H2CO3-->(H+) + (HCO3)
-HCO3 leaves cell and Cl- comes in the cell
What enzyme couples CO2 and H2O?
HCO3 leaves cell and Cl- comes in the cell
-What is this called?
-This process is occurring in the venous blood so venous blood has a lower plasma chloride (it's inside the cells)
What happens to HCO3 after it leaves the RBC?
It is converted back to CO2 and goes to the lungs
Benefits of altering the Hb-O2 curve?
-When do we see increases in CO2, temperature, and/or 2,3 DPG?
IN THE TISSUE
Compare and contrast O2 and CO2 transport
-O2 transport-volume carried in blood?
About 20 mL O2/dL blood
-O2 transport-major form of transportation?
Via heme in hemoglobin
-O2 transport-volume dissolved?
.3 mL O2/dL blood
-CO2 transport-Volume carried in the blood?
About 50 mL CO2/dL blood
-CO2 transport-Major form of transportation?
-CO2 transport-Volume dissolved?
About 3 mL CO2/dL blood
-CO2 transport-Other form of transportation?
Alveolar gas equation
-used to calculate?
-Used to calculate what inspired O2 needs to be to produce a desired alveolar (and therefore arterial) O2 level
What happens to the CO2 when it gets back to the lungs?
The CO2 moves into the alveoli
Alveolar gas equation
PAO2 = PIO2 - (PaCO2/R)
PAO2-alveolar partial pressure of oxygen
PIO2-inspired partial pressure of oxygen
(760-47) x oxygen %
On its own, being able to estimate the PAO2 is nice but not terribly useful
-However, it does allow us to calculate?
-Why is this useful?
the A-a O2 gradient-useful number for determining the health of the alveoli
-Normal is around 20 mmHg
-An increase in the A-a O2 gradient indicates a diffusion impairment (something is wrong with the alveoli)
Summary of the alveolar gas equation
-Allows us to predict?
-Allows us to predict the oxygen concentration in the alveoli (helpful since it is non-invasive)
-Once you have the alveolar concentration of oxygen (and you know the arterial concentration)- you can calculate the A-a O2 gradient
-If the A-a gradient is greater than normal you know there is a problem with the alveoli
-If the A-a gradient is normal, but the PaO2 and the PAO2 are both low, the problem is elsewhere (e.g. the patient may be hypoventilating)