4 - Gas Exchange Transport Flashcards
What is the equation for diffusion? What do the variables stand for?
Vgas = D * (A/T) * ∆P
Vgas = amount of gas diffused D = diffusion coefficient = [solubility/(molecular weight ^ 1/2)] A = surface area T = thickness ∆P = P1 - P2 = difference in pressure across the barrier
What is the equation for how much of a gas is dissolved in water? (Henry’s Law)
Solubility * partial pressure
O2diss = 0.003mlO2/dl/mmHg * PO2
CO2diss = 0.06mlCO2/dl/mmHg * PCO2
Why do O2 and CO2 diffuse at roughly the same rate even though CO2 is much more soluble?
There is a much bigger oxygen pressure gradient across the capillary-alveolus border
CO uptake is [perfusion/diffusion] limited, so it is used to measure the [perfusion/diffusion] capacity of the lung.
N2O uptake is [perfusion/diffusion] limited, so it is used to measure the [perfusion/diffusion] capacity of the lung.
CO - diffusion limited –> measure diffusion capacity
N2O - perfusion limited –> measure perfusion capacity
In healthy people, O2 and CO2 are [perfusion/diffusion] limited. In people with capillary-alveolar thickening, Pc[CO2/O2] might not reach equilibrium with the alveolar concentration.
perfusion limited
PcO2
What does an abnormally high A-aDO2 indicate?
A pathological problem with compromised gas exchange (ex: emphysema, pneumonia, asthma)
In normal resting conditions, hemoglobin has [1/2/3/4] O2 bound in systemic venous blood and [1/2/3/4] O2 bound in systemic arterial blood.
Venous - 3 bound O2 (75% saturated)
Arterial - 4 bound O2 (100% saturated)
(the 3 extra O2 represent a reserve capacity)
Why is it important to have dissolved oxygen in blood even though it does not greatly contribute to oxygen content?
- maintains PO2 necessary to keep hemoglobin saturated
- only free O2 can diffuse across cell membranes (not hemoglobin-bound O2)
How do you calculate the amount of oxygen delivered to resting tissue?
It is the difference between arterial O2 content and venous O2 content
[Increased/decreased] hemoglobin-O2 affinity means that it is easier to release O2 to the tissues
Decreased
[Increased/decreased] temperature leads to decreased hemoglobin-oxygen affinity and thus [increased/decreased] O2 delivery to the tissues.
Increased temp –> decreased affinity –> increased delivery
[Increased/decreased] pH leads to decreased hemoglobin-oxygen affinity and thus [increased/decreased] O2 delivery to the tissues.
Decreased pH –> decreased affinity –> increased delivery
[Increased/decreased] PCO2 leads to decreased hemoglobin-oxygen affinity and thus [increased/decreased] O2 delivery to the tissues.
Increased PCO2 –> decreased affinity –> increased delivery
[Increased/decreased] 2,3-DPG (aka 2,3-BPG) leads to decreased hemoglobin-oxygen affinity and thus [increased/decreased] O2 delivery to the tissues.
Increased 2,3-DPG –> decreased affinity –> increased delivery
How do CO and NO affect oxygen delivery?
They both competitively inhibit hemoglobin-O2 binding and shift the dissociation curve to the left (effectively increasing affinity and reducing delivery)
How does fetal hemoglobin affect O2 binding and delivery?
It has increased affinity and thus decreased delivery
How does methemoglobin affect O2 binding?
Methemoglobin cannot bind to O2
What are the 3 ways in which CO2 is transported in the blood?
- dissolved CO2 (6%; limited water solubility)
- bicarbonate (70%; formed by carbonic anhydrase from RBCs)
- carbamino compounds (24%; reaction with free amines on hemoglobin and other proteins)
What advantage does carbamino formation with hemoglobin confer?
It provides buffering to the blood
What is the Haldane effect (relates to O2 and CO2)?
There is an inverse relationship between binding of CO2 and O2 to hemoglobin.
Low O2 - hemoglobin can bind more CO2
High O2 - easier for hemoglobin to release CO2 in alveoli
What does pulse oximetry measure?
Oxygen saturation of arterial blood (SaO2) and pulse
