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18 Cards in this Set

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  • Back
Explain Diffusivity of CO2 versus O2.
Diffusivity = solubility/sqrt(MW)

CO2 has MW higher than O2. Hence, lower diffusivity. Howerver, CO2 is 24 times more soluble than O2 and so CO2's diffusivity is 20 times higher than that of O2.
Explain Lung diffusion capacity.
Lung diffusion capacity is a measure of how a specific gas is going to diffuse across a specific set of lungs (does not take into account partial pressures).

DL would decrease as A and D would decrease (emphysema, Tumors, Low CO, Low Blood volume) OR as T increases (fibrosis, edema)

PAo2 - 100mmHg
Pao2 - 40mmHg
PAco2 - 40mmHg
Paco2 - 45mmHg
Explain diffusion limited versus perfusion limited gas transport.
Diffusion limited - When even at the end of the capillary, partial pressure of the gas are no equal. This happnes when the gas is not able to diffuse easily (solubility or molecular weight are determinant factors - CO is an example)

Perfusion limited - is when the partial pressures are equal even before we get to the end of the capillary. (Blood flow is the determinant factor). Molecules with higher solubility are perfusion limited (N2O and O2 are examples)
How to improve N2O transfer across alveoli?
Increase blood flow - because N2O transfer is perfusion limited.
Explain O2 transport (perfusion versus diffusion limited) in normal conditions and during exercise.
Normal conditions - Partial pressure of O2 in the capillary equals out with alveolar real quickly (so the exchange is perfusion limited).

However, during exercise cardiac flow increases and so each RBC spends less time in the capillary and now the exchange is diffusion limited. (P02 has not reached equilibrium at the end of the capillary).
Explain O2 transport in fibrosis.
Fibrosis - means thickened wall (stiff lung). Increase T means lower DL and so diffusion is less. Hence, the O2 transport can become diffusion limited depending on severity of fibrosis.
Explain CO2 exchange for normal conditions.
The pressure gradient is less (beause 46 in capillary and 40 in alveoli). However, diffusivity is high so it takes just as much time as O2 to reach equilibrium.

It is perfusion limited.
Explain O2 exchange at higher altitudes.
At higher altitudes..PAo2 is 50mmHg and Pao2 is 25mmHg. So (P2-P1) is less hence it takes longer for O2 to diffuse across and so it becomes diffusion limited (even at the end of the capillary PAo2 is not equal to Pao2).
Relate shunt and dead space.
Shunt is when alvoli is blocked (hence no ventilation) so blood passes through without any gas exchange.

Dead space is when alvoli is ventilated but no blood is passing through. (functional dead space)
Decreased PO2 in arteries.
Decreased delivery of O2 to a tissue or decreased utilization.

Hypoxemia is one of the causes of Hypoxia.
Which O2 drives O2 diffusion?
Dissolved O2 (not O2 bound to Hb). Because this is the only O2 that contributes to the Po2.
Explain O2 supply per minute.
O2 concentration in 100ml of blood is 0.3ml. (when Po2 is 100 and solubility is .003).

CO is 5L/min.

Hence, O2 supply per minute is 15ml.
A pathologic state where O2 can not bind to Hb.

Fe is in the ferric state due to oxiation by nitrites or sulfonimides.
Explain O2 content.
O2 content is sum of (o2 in bound to Hb + dissolved o2).

dissolved o2 - Po2 * solubility

O2 about to Hb - (Hb capacity (20.1) * saturation)
Calculate Hb O2 carrying capacity.
1gm of Hb binds to 1.34ml o2.

100 ml blood has 15 gm Hb.

(15*1.34) = 20.1 ml of o2 carrying capacity per 100ml of blood.
How does CO poisoning effect Hb binding to O2.
CO has higher affinity for Hb.

Only 2 moles of O2 can bind if CO is bound to Hb. Plus, the affinity increases so the curve shifts to the left and so O2 is bound tightly to Hb and O2 delivery decreases.