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Flashcards in Diffusion and Perfusion Deck (14):
1

Define solubility coefficient and describe how they differ for oxygen and CO2.

the solubility coefficient for O2 is:
aO2 = 0.0013 mM/Torr.
Oxygen does NOT dissolve well in the blood

coefficient for CO2:
aCO2 = 0.03 mM/Torr
Carbon dioxide is 20 times more soluble in blood than oxygen

2

Describe the basic properties of the oxy-hemoglobin dissociation curve (ODC).

This curve relates oxygen saturation of hemoglobin, SO2, at equilibrium, to the PO2 in the blood

For PO2 = 100 Torr, which is normal arterial oxygen, SO2 = 97.5%

The standard ODC applies exactly only under the following conditions:
pH = 7.40; PCO2 = 40 Torr; temperature = 37 0
C; and [2,3-DPG] = 15 µmoles/gr Hb

3

Describe factors that promote rapid oxygen diffusion between alveoli and pulmonary capillaries in a healthy individual and how things can go wrong in disease.

The rate of gas transfer across an arbitrary tissue plane is a function of the (1) the difference in partial pressure of the gas on the two sides of the membrane, (2) the tissue plane
area, (3) the tissue thickness, and (4) a constant k reflecting the tissue solubility and molecular weight of the gas

Maximal diffusion: Large surface area, thin membrane, mechanism that helps maintain a large oxygen pressure gradient between alveoli and capillaries

4

Define perfusion and factors that influence it, including the effect of gravity

Perfusion, (Q ˙), is the blood flow of the pulmonary circulation available for gas exchange (in one minute)

5

Describe how gravity leads to regional variations in ventilation and perfusion in an upright person.

Because of gravity, the pulmonary blood pressure is low at the apex of the lung. At the base of the lung, the blood pressure is higher, allowing more capillaries to open and higher blood flow. Thus, perfusion increases as we go from the apex to the bottom of the lung.

6

Describe factors that promote rapid oxygen diffusion between alveoli and pulmonary capillaries in a healthy individual and how things can go wrong in disease.

x

7

Define perfusion and factors that influence it, including the effect of gravity

x

8

Describe the mechanisms by which dead-space, shunts, and V/Q mismatch impact gas exchange.

x

9

Describe how gravity leads to regional variations in ventilation and perfusion in an upright person.

x

10

Describe how diffusion can go wrong in disease.

During interstitial disease, when there is thickening of the alveolar walls, the rate of diffusion is slowed

Diffusion can also go down during emphysema, when breakdown in lung tissue decreases the surface area for diffusion

Abnormalities in the hemoglobin concentration:
polycythemia (when diffusion increases)
anemia (when perfusion decreases).
This can impact the pressure gradient for oxygen diffusion by altering free oxygen levels in blood.

11

Describe the mechanisms by which dead-space impact gas exchange.

Alveoli in unperfused regions of the lung are referred to as alveolar dead-space. Such a condition can happen if, for example, a patient has a blockage in a pulmonary capillary. These alveoli are well-ventilated, but because they do not engage in gas exchange, their ventilation is wasted

12

Describe the mechanisms by which shunts impact gas exchange.

A shunt is blood perfusion where there is no ventilation.
Shunts can decrease arterial oxygenation significantly, when the well-ventilated blood mixes with the shunted blood

13

Describe the mechanisms by which V/Q mismatch impact gas exchange.

V/Q is the ratio for the amount of ventilation versus perfusion
Because gravity has differing effects on the magnitude of ventilation and perfusion in different portions of the lung, there are resulting variations in the V/Q ratio (higher V/Q at the apex). When at high V/Q, cannot add very much more oxygen as compared to the normal V/Q because hemoglobin is already near saturation under normal V/Q conditions.

14

What are mechanisms that regulate the V/Q mismatch?

(1) In lung areas with high V /Q ratios, the alveolar PCO2 drops, leading to an increase in local airway resistance and
decreasing ventilation. Thus, V /Q tends to go down. (2) In lung areas with low V /Q ratios, the alveolar PO2 drops, leading to hypoxic vasoconstriction and decreasing local perfusion. Thus, V /Q tends to go up.