Respiration

Question 1

What is alveolar, arterial and venous PO2 in humans?

Answer 1

It is 102 torr, decreases to 95 torr in arterial blood and decreases to 40 torr in venous blood once consumed by tissues (Martin, 1999).

Question 2

Why is PO2 a bad measure of blood oxygen content?

Answer 2

It ignores the amount of oxygen bound to hemoglobin which exerts no pressure (Martin, 1999).

However any molecules still bound to hemoglobin aren’t being consumed anyways. PO2 is a maybe a good measure of equilibrium.

Question 3

How do we calculate oxygen content?

Answer 3

Hb (gm/dl) x 1.34 ml O2/gm Hb x SaO2 + PaO2 x (.003 ml O2/mm Hg/dl) (Martin, 1999).

Question 4

What is tissue normoxia?

Answer 4

The physiological oxygen tension the tissue routinely experiences.

Question 5

What is physiological PO2 in brain and during brain tumour?

Answer 5

Physiological brain PO2 is 35 torr and decreases to 13 torr in tumours (Assad, 1984) (Hoffman, 1996) (Dings, 1996) (tumor: Vaupel, 2007).

Question 6

What happens to turtle arterial PO2 near alveoli during dives? Are there any measurements of arterial PO2 near brain during normoxia?

Answer 6

Arterial PO2 falls from 100 to 20 torr during dives (Lutz, 2003). In right subclavian artery, PO2 was measured to be 22.7 torr during normoxia (Ultsch, 1982 I).

Question 7

(Sendroy 1934)

Answer 7

Looked at oxygen solubility of salt solutions and hemoglobin solutions. Found no difference between hemoglobin and red blood cell solutions when it came to oxygen solubility.

Question 8

What triggers changes in cerebral blood flow? Is it blood oxygen level or tissue oxygen level that is the signal?

Answer 8

Early work suggests that decreases in blood oxygen level trigger increases in cerebral blood flow. (Siesjo 1978)

Question 9

Does hypoxia increase cerebral blood flow in humans?

Answer 9

No, instead neurons seem to cope with hypoxia by increasing glycolysis (Mintun 2001). Not until arterial PO2 falls to 30 torr does cerebral blood flow begin to increase (Shimojyo 1968)

Question 10

What is the role of glycolysis in astrocytes and how might this translate to neurons?

Answer 10

Neuronal activity stimulated by glutamate tends to increase glycolytic metabolism in astrocytes. In astrocytes, glycolysis drives the metabolism of glutamate to glutamine before being recycled back into neurons. Glycolytic processing in astrocytes increase overproduction of lactate which is then taken by neurons and oxidatively metabolized.

Question 11

Is oxygen flux unidirectional in human brain?

Answer 11

Yes since there is minimal oxygen in brain tissue compared with blood (Kassissia 1995)

Question 12

What evidence is there that neurons might be able to tolerate PO2 as low as 30 torr?

Answer 12

Mintun’s (2001) model allows arterial PO2 to drop to 30 torr before neurons in the lethal zone experience 1 torr. Matches measurements by Shimojyo (1968) that show a large increase in CBF does not occur until arterial PO2 falls to 30-35 torr.

Question 13

Why do mammalian cells lack nuclei and organelles?

Answer 13

Removing nuclei and organelles, creates more space for hemoglobin. Prevents infection from blood cell targeting viruses. Reduces energy expenditure of maintaining organelles, and oxygen consumption by mitochondria.

Question 14

What organelles do turtle red blood cells have?

Answer 14

Turtle blood cells have nuclei but no organelles, not even mitochondria (Morgan 2009).

Question 15

What is one difference between the intermolecular interactions turtle and mammalian hemoglobin?

Answer 15

Readily polymerize under oxidizing conditions by possibly forming disulfide bridges (Sullivan and Riggs 1967).

Question 16

What is one mitochondrial factor that might limit oxygen diffusion into tissues?

Answer 16

Oxygen uptake might be limited by maximal rate of turnover of enzymes in the Kreb’s cycle (Blomstrund 1997).

Question 17

How does deformation of RBCs in the peripheral vessels enhance oxygen delivery?

Answer 17

Increases intracellular convection currents. Encourages diffusion of oxygen out of RBCs (Zander 1973).

Question 18

How much more stronger does CO bind hemoglobin than O2?

Answer 18

CO binding of hemoglobin is 240 times stronger than O2.

Question 19

How much of blood oxygen content do tissues take up on average?

Answer 19

Approximately 20-25% of blood oxygen content is used by tissues, and up to 80% during exercise.

Question 20

(Aberman 1973)

Answer 20

Derived an equation for O2 Dissociation Curve based on Hasting’s approximations. Not good for in vivo because P50 changes a lot in vivo. However still good for a single volume measurements.

Question 21

(Ackerman 1979)

Answer 21

Voluntary diving is terminated when lung gas PO2 drops to 22 torr.

Nonpulmonary CO2 loss is minor in turtles and not the major cause of changes in lung volume. Instead CO2 production rate far exceeds CO2 flux.

Respiratory Exchange Coefficient becomes increasingly less than the Respiratory Quotient at larger values.

Mean RQ in turtles is 0.75.

L-R Shunting reduces CO2 entering lung gases.

Predicted maximum diving time of 45 minutes. In close agreement with observed diving time of 44 minutes. Night-time diving times are 71% longer than predicted, and VO2 is 61% lower.

Question 22

What is the respiratory quotient?

Answer 22

The proportion of VCO2 to VO2.

Question 23

(Berkson 1966)

Answer 23

Approximately 15 h required to re-establish predive lactate levels.