11-1: Gas Exchange

Front 1

Boyle's Law

Back 1

P1V1=P2V2

Front 2

Dalton's Law

Back 2

Partial pressures of gas in mixture of gases is pressure gas would exert if occupied total volume of mixture.

i.e., the total pressure exerted by a gaseous mixture is equal to the sum of the partial pressures of each individual component in a gas mixture.

Front 3

Henry's Law

Back 3

Partial pressure of a gas in liquid phase (dissolved) = partial pressure in gas phase

Front 4

Equation to convert partial pressure of gas in liquid phase to concentration of gas in liquid phase.

Back 4

Cx = Px x Solubility

Front 5

Concentration of gas in solution applies only to gas that is _____ and ________ in solution.

Back 5

Concentration of gas in soln applies only to DISSOLVED, FREE (not bound to protein) gas.

Front 6

Fick's Law

Back 6

In simple diffusion, rate of diffusion (Ṿx) directly proportional to partial pressure difference of gas, NOT concentration.

Front 7

Equation for calculating rate of diffusion.

Back 7

Ṿx = [DA∆P]/∆x

Front 8

Diffusion coefficient (D) vs Lung Diffusing Capacity (DL):
Factors affecting each

Back 8

Diffusion coefficient: depends on MW, solubility

DL: depends on D, A, ∆x, and time to bind proteins (Hgb); usually measured w/CO

Front 9

Effect of emphysema on DLCO.

Back 9

Dec'd bc dec'd SA (alveolar destruction)

Front 10

Effect of fibrosis on DLCO.

Back 10

Dec'd bc ∆x increases

Front 11

Effect of pulmonary edema on DLCO.

Back 11

Decreases bc ∆x increases

Front 12

Effect of anemia on DLCO.

Back 12

Decreases bc Hgb decreases

Front 13

Effect of exercise on DLCO.

Back 13

Increases bc add'l capillaries perfused w/blood, increasing SA for gas exchange.

Front 14

Effect of height on DLCO.

Back 14

Height directly related to lung volume; Tall people have higher DLCOs.

Front 15

What is the normal transit time of blood through the alveolar capillary? Is this enough time for PO2 equilibration to occur?

Back 15

Normal transit time of blood through alv capillary is 0.75 seconds.

Takes 0.25 seconds for PO2 equilibration to occur

SO under normal conds, capillary blood leaving alveolus has fully equilibrated w/O2

Front 16

Only ____ gas molecules in a solution contribute to partial pressure.

Back 16

Dissolved

Front 17

This gas is never bound or modified in solution.

Back 17

Nitrogen

Front 18

These gases bind proteins in blood.

Back 18

O2, CO2, CO

Front 19

These gases bind Hgb in addition to albumin.

Back 19

O2, CO

Front 20

Provide an example of a chemically modified gas in solution (blood).

Back 20

CO2-->HCO3- via carbonic anhydrase

Front 21

Dry Inspired Air vs Humidified Tracheal Air:
PO2
PCO2

Back 21

Dry Inspired air has a PO2 ~160mmHg, PCO2 = 0

Humidified tracheal air is fully saturated w/H2O vapor and PO2 is 'diluted' by H2O vapor

PCO2 = 0

Front 22

CO2 transfer to alveolar air is equal to __________.

Back 22

CO2 production by body

Front 23

How does arterialized PO2 differ from alveolar PO2? Why?

Is this a normal process?
How does this affect the A-a gradient?

Back 23

Arterialized PO2 is slightly lower than alveolar PO2 bc small fraction of pulmonary blood that bypasses alveoli is not arterialized.

Occurs normally due to bronchial blood flow and coronary venous blood draining directly into LV.

Creates a small/negligible A-a gradient (known as physiologic shunting).

Front 24

Diffusion vs Perfusion Limited Gas Exchange:
General
Examples

Back 24

Diffusion-Limited: total amount of gas transported across alveolar-capillary barrier limited by DIFFUSION; ex: CO, O2 during exercise/emphysema/fibrosis

Perfusion-limited: total amount of gas transported limited by blood flow through capillaries; ex: N2O, O2 under normal conditions, CO2

Front 25

Why is CO considered a diffusion-limited gas?

What other gases are considered diffusion-limited?

Back 25

At beginning of capillary, PaCO is 0 and there's largest partial pressure gradient for CO (largest driving force of diffusion). Moving along capillary, as CO diffuses, PaCO rises and gradient decreases, but PaCO rises only slightly bc CO avidly bound to Hgb (no longer free-->no more partial pressure).

Thus, maintains gradient along entire length of capillary and CO does not equilibrate.

O2 behaves this way during strenuous exercise, emphysema, fibrosis

Front 26

Why is N2O considered a perfusion-limited gas?

What other gases are perfusion limited?

Back 26

N2O not bound in blood and exists entirely free in solution.

Initially very large partial pressure gradient, N2O rapidly diffuses. Bc all N2O free in blood, creates a partial pressure rapidly and fully equilibrates w/alveolar gas in first fifth of capillary. No more gradient-->no more diffusion.

Only way to increase net diffusion of N2O is by increasing blood flow.

O2 behaves this way under normal conditions, as does CO2

Front 27

What is the effect of fibrosis on O2's diffusion limitations?

Back 27

In fibrosis, alveolar walls thicken, increasing ∆x, decreasing DL, and slowing diffusion. Equilibration of O2 doesn't occur and gradient maintained along entire length of capillary.

Although gradient maintained for longer length of capillary, total transfer of O2 still DECREASED.

Thus, fibrosis makes O2 transport diffusion-limited.

Front 28

What is the effect of high altitudes on O2 diffusion?

Back 28

High altitude-->low barometric pressure-->Low PAO2-->Low partial pressure gradient-->dec'd diffusion

Equilibration occurs more slowly along capillary and occurs at later point.