Blood Gas Transport Flashcards
What is the mutation of sickle cell disease?
it is caused by a single-base mutation in the beta chain of hemoglobin. the sixth amino acid in the chain is converted from glutamic acid to valine
What is the alveolar gas equation?
PAO2 = PIO2 - PACO2/RQ
How do you solve for PIO2?
(Pb-Ph2o) * FO2
Ph2o should be 47
FO2 is usually 0.21 unless stated otherwise
How do you solve for RQ?
VCO2/VO2 = CO2 produced / O2 consumed
should be about 0.8
How to solve for oxygen concentration?
Pressure (PAO2) * Solubility of O2
What is dissolved oxygen delivery?
15mL O2/min
What is hemoglobin
protein complex consisting of four polypeptide chains (2 alpha and 2 beta chains) each containing a heme group that reversibly binds with O2
Hb + O2 <–> HbO2
deoxyhemoglobin <–> oxyhemoglobin
without hemoglobin… alveolar O2 diffuses down its pressure gradient and PAO2
increases to equilibration
with hemoglobin… O2 is quickly bound in the blood and is no longer exerting pressure. this maintains a
low blood PO2 that maintains a pressure gradient for additional diffusion
CO2 exchange at alveoli
PCO2 is at a steady state
alveolar PCO2 is maintained
bc of a greater CO2 solubility…
a similar volume of gas is exchanged with a smaller pressure gradient
Oxygen Dissociation Curve:
PaO2 =
PvO2 =
only ___ of the O2 delivered to the tissues is extracted
at a lower PvO2, ___ of the O2 can be extracted
PaO2 = 100mmHg and 95% saturation
PvO2 = 40mmHg and 75% saturation
~20-25%
~70%
Oxygen Dissociation Curve:
the plateau assures what?
the steep curve enables what?
the plateau assures saturation of Hb
the steep curve enables greater unloading
Hemoglobin’s affinity for O2 is measured by the pressure required to saturate Hb to
50%
Will a decrease in Hb-O2 affinity shift the ODC to the left or right?
right
Will a decrease in Hb-O2 affinity be beneficial at the tissues or lungs?
tissues
What is the Bohr effect?
the rightward shift of the ODC due to a fall in pH (decreased affinity = increased P50)
All of the following will promotes the release of oxygen from oxyhemoglobin (shift to right) except…
a) increased carbon dioxide conc
b) increased blood temp
c) increased pH
d) increased 2,3 DPG
c) increased pH
left shift on ODC
decrease P50
increased affinity
decrease temp
decrease PCO2
increase pH
decrease 2,3 DPG
right shift on ODC
increase P50
decrease affinity
increase temp
increase PCO2
decrease pH
increase 2,3 DPG
Blood oxygen content =
it is dependent on…
dissolved O2 + bound HbO2
1. PO2 and gas solubility
2. Hb conc.
3. Hb-O2 saturation
What is hypoxic hypoxia?
the blood contains an abnormally low PO2. this can occur during hypoventilation and when PIO2 is low such as at high altitude
What is anemic hypoxia?
PO2 is normal but Hb conc is low. oxygen content is reduced. occurs with carbon monoxide poisoning
What is hypoperfusion hypoxia?
aka circulatory, ischemia or stagnant hypoxia. may occur if there is a reduction in tissue blood flow
What is histotoxic hypoxia?
occurs when exposed to cyanide. O2 conc. ov venous blood is high
Carbon Dioxide transport:
1) carbamino compound
carbamino compound: CO2 binds Hb and Proteins
Deoxyhemoglobin has a greater affinity for CO2 than oxyhemoglobin (haldane effect)
accounts for ~5% of transport
Carbon dioxide transport
3) dissolved
CO2 is 20x more soluble than O2
account for ~5% of transport
Carbon dioxide transport
2) bicarbonate
CO2 is converted to bicarbonate by carbonic anhydrase
accounts for 90% of CO2 transport.
occurs in RBCs
Tissue: Mechanism for Carbon Dioxide Exchange
big CO2 + H2O –> H2CO3 –> H + HCO3 (rxn favors right side of eq)
1. CO2 diffuses into blood and RBCs
2. CO2 binds Hb: high affinity for Hb v HbO2 (haldane effect)
3. CO2 will combine with H2O via carbonic anhydrase to form H+ and HCO3
Tissues: Carbon Dioxide Exchange
H+ and HCO3 accumulate in RBCs (rxn favors right side of eq)
1. H binds Hb
2. HCO3 exchanged for Cl to maintain electrical neutrality
3. chemcial rxn continues
4. HCO3 more solubel than CO2
Lung: Carbon Dioxide Exchange
small CO2 + H2O <– H2CO3 <– H + HCO3 (rxn favors left side of eq)
low CO2 pressure in lung creates pressure gradient required to drive rxns
1. CO2 and H released from Hb
Co2 diffuse to lung
Hb is free to bind O2
H is free to bind HCO3
2. Cl is exchanged for HCO3
3. CO2 is free to diffuse to lung
Key point for At TISSUES:
tissues have lower PO2 –>
lower HbO2 saturation facilitates…
lowers HbO2 saturation
CO2 binding and transport of CO2 as HbCO2
At the tissues:
Bohr effect
low pH –> decreases HbO2 affinity with promotes oxygen unloading
At the tissues:
Haldane effect
low HbO2 saturation –> facilitates HbCO2 binding and CO2 transport
At the tissues, both the Bohr and Haldane effects work together to…
increase O2 delivery and CO2 uptake from the tissues
At the lung:
CO2 is exhaled and pH increases
this increases HbO2 affinity, which increases HbO2 saturation, which facilitates CO2 unloading from Hb
both effects maximize O2 uptake and CO2 delivery at lungs
