Oxygen Transport

Question 1

Describe the overall features of oxygen transport in the blood:

1) including the amount of dissolved oxygen
2) the amount of oxygen bound to hemoglobin
3) the main features of the normal oxygen dissociation curve and its regulation by pH, PCO2, temperature and 2,3-DPG.

Answer 1

1) @ 100mmHg = 0.3%. Also, your tissues cannot extract all of the Oxygen from this .3%. (multiply this by CO for % vol O2)–so this is not enough Oxygen for the needs of the body. See pg 234.
2) Hemoglobin increases the amount of bound oxygen in the blood–which is MORE than sufficient for the needs of the body.
3) CADET Turn Right: Increasing CO2, Acid, DPG-BPG, exercise, increase temperature shift right. See pg. 236-240**.

Question 2

Describe Fick’s law of oxygen transport and how it is used to measure cardiac output. VO2 =

Answer 2

Oxygen consumption by the tissues, VO2, is related to cardiac output, CO, and the A-V oxygen concentration difference as follows:

VO2 = CO (CaO2 - CvO2)

VO2 = CO x E

or

E = VO2/CO

Extraction is the difference between arterial & venous blood (Ca or Cv O2 is % volume O2) typically is, E = CaO2 - CvO2 = 20% - 15% = 5%

VO2 is measured by comparing the amount inspired vs expired. so VO2net = VO2insp - VO2exp

Question 3

Distinguish between oxygen content, percent saturation, extraction and the partial pressure of oxygen in the blood.

Answer 3

O2 content is net O2 content

Saturation is #O2/Hb

Extraction is the difference between arterial & venous blood

Partial pressure O2 is the partial pressure in comparison to all the other blood gases

Question 4

Describe how oxygen content, percent saturation, extraction and the partial pressure of oxygen in the blood is altered in:
1) polycythemia

Answer 4

More RBC, more Hb, so curve shift left & up

HOWEVER THE CURVES ARE ALL IDENTICAL IN TERMS OF SATURATION OR P50–IT IS OXYGEN CONTENT THAT CHANGES

This is called blood doping & is cheating in sports since it increases endurance. Increasing Hb naturally occurs when you go to live @ high altitude due to increased erythropoerin.

See pg. 238

Question 5

Describe how oxygen content, percent saturation, extraction and the partial pressure of oxygen in the blood is altered in:
2) anemic hypoxia

Answer 5

Less Hb, curve shift right & down

HOWEVER THE CURVES ARE ALL IDENTICAL IN TERMS OF SATURATION OR P50–IT IS OXYGEN CONTENT THAT CHANGES

Anemic hypoxia is characterized by normal PaO2 but LOW CaO2, with NORMAL extraction and therefore low PvO2. Causes include iron deficiency anemia or congenital hemolytic anemias such as sickle cell anemia.

See pg. 238

Question 6

Describe how oxygen content, percent saturation, extraction and the partial pressure of oxygen in the blood is altered in:
3) hypoxic hypoxia

Answer 6

Hypoxic hypoxia is characterized by LOW PaO2 (hypoxemia) and low CaO2 with NORMAL extraction and therefore low PvO2. Causes include high altitude, diffusion problems, and hypoventilation.

High altitude

See pg. 243-244

Question 7

Describe how oxygen content, percent saturation, extraction and the partial pressure of oxygen in the blood is altered in:
4) stagnant hypoxia

Answer 7

When patient has congestive heart failure, blood flows slowly & CO is decreased. Extraction is increased.

Stagnant hypoxia is characterized by normal PaO2 and CaO2, INCREASED extraction and therefore low PvO2. Causes include a sluggish circulation due to low cardiac output as occurs in congestive heart failure.

See pg. 243-244

Question 8

Describe how oxygen content, percent saturation, extraction and the partial pressure of oxygen in the blood is altered in:
5) histotoxic hypoxia

Answer 8

Histotoxic hypoxia is characterized by normal PaO2 and CaO2 with DECREASED extraction and elevated PvO2. Causes include poisoning of tissue metabolism by heavy metals, cyanide or other toxins.

See pg. 243-244

Question 9

Describe how oxygen content, percent saturation, extraction and the partial pressure of oxygen in the blood is altered in:
6) Anemic hypoxia

Answer 9

Anemic hypoxia is characterized by NORMAL PaO2 but low CaO2, with NORMAL extraction and therefore low PvO2. Causes include iron deficiency anemia or congenital hemolytic anemias such as sickle cell anemia.

See pg. 243-244

Question 10

What are the partial pressures of O2 & CO2 in the venous blood?

Answer 10

O2 = 40mmHg
CO2 = 46mmHg, CO2 therefore diffuses into the alveolar compartment to breathe out

Question 11

What are the partial pressures of O2 & CO2 in the Alveoli?

Answer 11

O2 = 100mmHg
CO2 = 40mmHg

Question 12

What are the partial pressures of O2 & CO2 in the End-Capillary blood?

Answer 12

O2 = 100mmHg
CO2 = 40mmHg

It is the same as the alveolar compartment.

Question 13

Thus the normal arterio-venous, or A-V, PO2 difference is

Answer 13

Thus the normal arterio-venous, or A-V, PO2 difference is: 100 - 40 = 60 mm Hg.

Question 14

What is the function of Erythropoietin?

Answer 14

Erythropoietin (kidney hormone) increases the production of red blood cells, under hypoxic conditions.

Living @ high altitude stimulates Erythropoietin to make more RBC’s.

Question 15

Carbon monoxide poisoning

Answer 15

It increases O2 binding affinity (left shift) & it increases CO binding to hemoglobin (it displaces oxygen & increases oxygen binding affinity). Therefore it reduces O2 delivery to tissues.

See pgs. 245 - 246

Question 16

Tissue Po2 is a balance between delivery and usages. With a decrease in blood flow, with ____ change in metabolism there will be a _____ in venous Po2 and an ______ in venous Pco2.

Answer 16

Tissue Po2 is a balance between delivery and usages. With a decrease in blood flow, with no change in metabolism there will be a decrease in venous Po2 (less delivery but no change in metabolism) and an increase in venous Pco2 (less washout).

Question 17

The oxygen carrying capacity of the blood is _______ in an anemic person, but the arterial Po2 and oxygen saturation of hemoglobin are both _____. The decrease in arterial oxygen content is compensated for by an increase in the extraction of oxygen from hemoglobin, which ______ the Po2 of the venous blood. The unloading of oxygen at the tissue level is enhanced by increased levels of ________ in an anemic patient because it causes a right-shift of the oxygen-hemoglobin dissociation curve.

Answer 17

The oxygen carrying capacity of the blood is reduced in an anemic person, but the arterial Po2 and oxygen saturation of hemoglobin are both normal. The decrease in arterial oxygen content is compensated for by an increase in the extraction of oxygen from hemoglobin, which reduces the Po2 of the venous blood. The unloading of oxygen at the tissue level is enhanced by increased levels of 2,3 diphophosglycerate (2,3 DPG) in an anemic patient because 2,3 DPG causes a right-shift of the oxygen-hemoglobin dissociation curve.