Ventilation Flashcards
which airways are conducting? What is their average volume.
0-16, 150ml
RQ and average values. What changes it?
Vco2/Vo2
200/250=0.8
Changed by metabolism and diet (Carbs=1.0, lipids=0.7, protein=0.83)
Approximate the alveolar gas equation
PAO2=PIO2-(PACO2/RQ)
What are normal values for alveolar air
PAO2=80-100
PACO2=35-45
diffusion limited
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
perfusion limited
Perfusion limited is the opposite. It is limited by how much blood flows thru. These are insoluble gases. Rate of diffusion>capacitance of blood
How does the diffusion rate of CO2 compare to O2
pretty much equal
What is the normal venous PCO2?
45mmHg.
what slows equilibration of CO2?
formation of bicarb, combining w/ hemoglobin
Effect of disequilibrium on PCO2 and PO2
greater effect on PO2 b/c it has a smaller diffusion coefficient
How much O2 is dissolved in the blood normally
0.3 vol% (need at least 5 vol% to sustain life), less than 5% of transported O2 is dissolve
what is the Oxygen capacity of Hb? What affects it?
max amt of O2 that can bind to Hb. Affected by amt of Hb present but not affinity.
What is the P50?
expression of affinity. Pressure at which 50% saturation. Normally 27 mmHg. Not affected by Hb conc.
what are normal figure for O2 capacity and O2 content?
capacity= 20.1 vol%
content=19.6 vol%
Does changing Hb conc alter capacity? P50? %saturation?
yes, no, no
3 things that increase P50
Increased temp
Bohr effect
Increased 2,3-DPG
Bohr effect
lower pH and higher CO2 conc increase P50 (rightward shift). Deoxyhemoglobin is a weaker acid than oxyhemoglobin (ie, more readily accepts H+)
what catalyzes the hydration of CO2? Where is it present?
carbonic anhydrase, present in RBC’s but not plasma.
chloride shift
bicarb out of cell and chloride in to preserve electrically neutrality
what is formed when CO2 combines with Hb?
HbNH-COOH
Haldane Effect
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
What are the relative contributions to CO2 transport of the various mechanisms?
HCO3- >carbamino > dissolved. Decreased HCO3- and increased carbamino and dissolved contribution to released.
What is a normal A-a difference? When is it most useful?
<10mmHg. In pts breathing room air since A-a increases with supplemental O2
P/F ratio. what is normal?
PaO2 to FIO2. Regardless of FIO2, P/F should be >450
what is the normal blood pH? PCO2?
7.4, 40mmHg
PaCO2 equation
(V(dot)CO2/0.863)/(V(dot)E(1-(VD/VT)))
what is the most likely cause of hypocapnia
increased VE
what are likely causes of hypercapnia
Increased VCO2
Decreased VE
Increased Vd/Vt
hypercapnia often reflects imbalance between ___&___
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
How much O2 do you give to a COPD pt?
Just enough to oxygenate (~90%) b/c you also cause increase in PCO2
