Respiratory Phys - Oxygen Deprivation, VQ mismatch

Question 1

Causes of Hypoxemia with Normal A-a gradient:

Answer 1

High altitude

Hypoventilation

Question 2

Causes of Hypoxemia with Increased A-a gradient:

Answer 2

V/Q mismatch (shunts blood away from alveoli)
Diffusion limitation (Pulmonary Fibrosis)
Right-to-left shunt

Question 3

Causes of Hypoxia (decreased O2 delivery to tissue)

Answer 3

Decreased CO
Hypoxemia
Anemia
CO poisoning

Question 4

Causes of Ischemia (loss of blood flow):

Answer 4

Impeded arterial flow (MI, Stroke)

Decreased venous drainage

Question 5

Hypoxemia:

Answer 5

Decreased PaO2

Question 6

Hypoxia:

Answer 6

Decreased O2 delivery to tissue

Question 7

Ischemia:

Answer 7

Loss of blood flow

Question 8

V/Q mismatch: Apex - V/Q =

Answer 8

V/Q = 3 (wasted ventilation)

Decreased ventilation leads to even more decrease in perfusion, which causes V/Q ratio to increase

Question 9

V/Q mismatch: Base - V/Q =

Answer 9

V/Q = 0.6 (wasted perfusion)

Increased ventilation leads to even more increase in perfusion, which causes V/Q ratio to decrease

Question 10

Greatest zone of ventilation:

Answer 10

Zone 3, the base

Question 11

Greatest zone of perfusion:

Answer 11

Zone 3, the base

Question 12

With exercise, how does V/Q change?

Answer 12

Have increased CO, and vasodilation of apical capillaries, resulting in V/Q ration that approaches 1.

Question 13

Organisms that thrive in high O2, flourish in the:

Answer 13

apex

ex. TB

Question 14

What causes V/Q to approach 0?

Answer 14

Airway obstruction (shunt). 
In shunt, 100% O2 does not improve PO2 (because can't ventilate)

Question 15

What causes V/Q to approach infinity?

Answer 15

Blood flow obstruction (physiologic dead space). Assuming <100% dead space, 100% O2 improves PO2!

Question 16

Zone 1

Answer 16

PA > Pa > Pv

Question 17

Zone 2

Answer 17

Pa > PA > Pv

Question 18

Zone 3

Answer 18

Pa > Pv > PA

Question 19

CO2 is transported from tissues to the lungs in 3 forms:

Answer 19

HCO3- (90%) carried in the plasma
Carbaminohemoglobin or HbCO2 (5%)
Dissolved CO2 (5%)

Question 20

Where is CO2 bound in carbaminohemoglobin?

Answer 20

Bound to Hb at N-terminus of globin. (NOT HEME!)

Question 21

CO2 binding favors which form of Hb?

Answer 21

Taut (O2 unloaded)

Question 22

CO2 + H2O —enzyme?——-> H2CO3

Rxn takes place in ?

Answer 22

Carbonic Anhydrase

RBC

Question 23

H2CO3 dissociates to ——>

Answer 23

H+ and HCO3-

Question 24

HCO3- is transported out of the RBC via

Answer 24

HCO3-/Cl- antiporter

Question 25

Haldane Effect

Answer 25

In lungs, oxygenation of Hb promotes dissociated of H+ from Hb. This shifts equilibrium toward CO2 formation; CO2 is released from RBCs

Question 26

Bohr Effect

Answer 26

In peripheral tissue, increased H+ from tissue metabolism shifts curve to right, unloading O2

Question 27

Response to high altitude

Answer 27

Decrease atmospheric O2 --> Decreased PaO2 --> increased ventilation ---> Decreased PaCO2 Increased erythropoietin --> Increased hematocrit and Hb Increased 2,3-BPG (binds Hb so that Hb releases more O2) Cellular changes (increased mitochondria) Increased renal excretion of HCO3- to compensate for respiratory alkalosis (can augment with Acetazolamide) Chronic hypoxic pulmonary vasoconstriction results in RVH

Question 28

Acetazolamide

Answer 28

Carbonic Anhydrase inhibitor which can be used to treat altitude sickness (to increase excretion of bicarb and balance out respiratory alkalosis), and is also a diuretic

Question 29

Response to Exercise

Answer 29

Increased CO2 production Increased O2 consumption Increased ventilation rate to meet O2 demand V/Q ratio from apex to base becomes more uniform Increased pulmonary blood flow due to increased CO Decreased pH during strenuous exercise (2ndary to lactic acidosis) No change in PaO2 and PaCO2, but INCREASE in venous CO2 content, and DECREASE in venous O2 content