33 terms

# Oxygen Transport

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How much oxygen can 1g of Hb carry?
1.34mL.
What is CaO2?
Ratio of oxygen volume to arterial blood volume =
(A) Hb X 1.34mL/g * SaO2 +
(B) PaO2 * 0.003.
What is DO2?
Oxygen delivery in L/min = CO * CaO2
What is VO2?
Oxygen consumption in L/min = CO * (CaO2 - CvO2)
What is the O2 extraction ratio?
VO2/DO2.
How long does it take for oxygen to diffuse into capillaries across alveoli epithelial lining?
1/4 second, with 3/4 second of contact time at rest and 1/4 during vigorous exercise.
What is a normal CaO2?
20mL/100mL.
What is normal VO2?
250 mL/min.
What is normal DO2?
1000 mL/min.
What is a normal ER?
25%.
What is normal PaO2?
100.
How much oxygen is dissolved in arterial blood?
0.3 mL O2 / dL arterial blood, so if CO is 5 L/min, that would lead to a normal DO2 of 15 mL/min.
Why is the oyxgen carrying capacity of Hb 1.34?
Because of non-functional or met-hemoglobin, not all hemoglobin can carry all four molecules of oxygen, so even though 4mol O2/mol Hb 22.4L O2/mol O2 mol Hb / 64,500g = 1.39, we use 1.34.
What is the normal CaO2?
20mL/dL, assuming an oxygen saturation of 100.
What is normal CvO2?
15mL/dL, assuming an oxygen saturation of 75.
How does the sigmoidal shape for Hb-O2 binding help?
Flat upper portion leads to tight binding across a range of PAO2, and steep lower portion leads to easy disassociation in tissues.
What causes left-shift?
Decrease in temperature, [H+], 2-3DPG, as well as CO.
What causes right-shift?
Increases in temperature, [H+], 2-3DPG.
Why is it great that low [H+]/high pH causes left-shift?
If you start hyperventilating because of low air O2 content, such as on Mt. Everest, you will cause respiratory alkalosis that left shifts the curve and makes it easier for Hb to bind O2.
Does CvO2 go down in exercise?
Yes, extraction ratio changes from 25% to 50%.
Doe extraction ratio go up in exercise?
Yes, CvO2 goes down from 15 to 10.
Does reduction in oxygen delivery change oxygen consumption?
Yes, at a certain point, anaerobic metabolism takes over and oxygen consumption decreases.
Why does oxygen consumption not drop before the threshold as delivery drops?
(1) that increase ER,
(2) that maintain DO2 despite fall in CaO2.
What factors influence ER?
(1) Distribution of CO to higher-uptake tissues,
(2) Increase in capillary perfusion,
(3) Shortening capillary-cell diffusion distance,
(4) Metabolic demand!
How does sepsis influence ER?
Sepsis interferes with body's ability to modulate ER:
(1) Vasodilation creates shunting.
(3) Edema leads to decreased cell O2 uptake,
(4) Mitochondria become decoupled, leading to inefficient use of O2.
In sepsis, is O2 consumption high or low?
It can be high, but as delivery falls, consumption falls because vascular changes cannot compensate to increase ER.
What travels faster through tissue, O2 or CO2?
CO2 travels 20x faster.
What causes a normal A-a gradient?
5 mmHg due to shunting from alveoli to pulmonary capillaries and from capillaries to arterioles.
What tissue PO2 is safe?
25 mmHg is normal between two adjacent capillaries, 3-4 is all that is necessary, but 0 would be quite bad!
What are the types of hypoxia?
(1) Hypoxic,
(2) Hypoxemia,
(3) Circulatory,
(4) Histotoxic.
How does CO interfere with DO2?
Lowers CaO2, but also shifts the curve to the left, leading to low-release.
Does SaO2 measure only oxyhemoglobin?
No, it also falsely measures carboxyhemoglobin.
Does CO also interfere with VO2?
Yes, it blocks cytochrome oxidase.