Ventilation

Question 1

which airways are conducting? What is their average volume.

Answer 1

0-16, 150ml

Question 2

RQ and average values. What changes it?

Answer 2

Vco2/Vo2
200/250=0.8
Changed by metabolism and diet (Carbs=1.0, lipids=0.7, protein=0.83)

Question 3

Approximate the alveolar gas equation

Answer 3

PAO2=PIO2-(PACO2/RQ)

Question 4

What are normal values for alveolar air

Answer 4

PAO2=80-100

PACO2=35-45

Question 5

diffusion limited

Answer 5

diffusion limited-limited by diffusion across membrane, increase in capillary flow doesn’t change it. These are soluble gases. By definition: PAg is not equal to Pc’g

Question 6

perfusion limited

Answer 6

Perfusion limited is the opposite. It is limited by how much blood flows thru. These are insoluble gases. Rate of diffusion>capacitance of blood

Question 7

How does the diffusion rate of CO2 compare to O2

Answer 7

pretty much equal

Question 8

What is the normal venous PCO2?

Answer 8

45mmHg.

Question 9

what slows equilibration of CO2?

Answer 9

formation of bicarb, combining w/ hemoglobin

Question 10

Effect of disequilibrium on PCO2 and PO2

Answer 10

greater effect on PO2 b/c it has a smaller diffusion coefficient

Question 11

How much O2 is dissolved in the blood normally

Answer 11

0.3 vol% (need at least 5 vol% to sustain life), less than 5% of transported O2 is dissolve

Question 12

what is the Oxygen capacity of Hb? What affects it?

Answer 12

max amt of O2 that can bind to Hb. Affected by amt of Hb present but not affinity.

Question 13

What is the P50?

Answer 13

expression of affinity. Pressure at which 50% saturation. Normally 27 mmHg. Not affected by Hb conc.

Question 14

what are normal figure for O2 capacity and O2 content?

Answer 14

capacity= 20.1 vol%

content=19.6 vol%

Question 15

Does changing Hb conc alter capacity? P50? %saturation?

Answer 15

yes, no, no

Question 16

3 things that increase P50

Answer 16

Increased temp
Bohr effect
Increased 2,3-DPG

Question 17

Bohr effect

Answer 17

lower pH and higher CO2 conc increase P50 (rightward shift). Deoxyhemoglobin is a weaker acid than oxyhemoglobin (ie, more readily accepts H+)

Question 18

what catalyzes the hydration of CO2? Where is it present?

Answer 18

carbonic anhydrase, present in RBC’s but not plasma.

Question 19

chloride shift

Answer 19

bicarb out of cell and chloride in to preserve electrically neutrality

Question 20

what is formed when CO2 combines with Hb?

Answer 20

HbNH-COOH

Question 21

Haldane Effect

Answer 21

oxyhemoglobin is stronger acid than deoxyhemoglobin. In lungs you have lots of HHb and O2 you get equilibrium shift in opposite direction from Bohr effect

Question 22

What are the relative contributions to CO2 transport of the various mechanisms?

Answer 22

HCO3- >carbamino > dissolved. Decreased HCO3- and increased carbamino and dissolved contribution to released.

Question 23

What is a normal A-a difference? When is it most useful?

Answer 23

<10mmHg. In pts breathing room air since A-a increases with supplemental O2

Question 24

P/F ratio. what is normal?

Answer 24

PaO2 to FIO2. Regardless of FIO2, P/F should be >450

Question 25

what is the normal blood pH? PCO2?

Answer 25

7.4, 40mmHg

Question 26

PaCO2 equation

Answer 26

(V(dot)CO2/0.863)/(V(dot)E(1-(VD/VT)))

Question 27

what is the most likely cause of hypocapnia

Answer 27

increased VE

Question 28

what are likely causes of hypercapnia

Answer 28

Increased VCO2
Decreased VE
Increased Vd/Vt

Question 29

hypercapnia often reflects imbalance between ___&___

Answer 29

drive and load. Decreased drive=ALS (no reserve for when you get a tiny infection) Increased load: may be fit but have a severe asthma attack

Question 30

How much O2 do you give to a COPD pt?

Answer 30

Just enough to oxygenate (~90%) b/c you also cause increase in PCO2