11-1: 11/29: Gas Exchange

Front 1

What does Dalton's Law state?

Back 1

Total pressure exerted by a gas mixture is sum of all of partial pressures of component gases

Front 2

What is Brownian motion?

Back 2

Diffusion of gas is net result of random movements of gas molecules; results from the kinetic energy of the molecules (temperature)

Front 3

What does Henry's Law state?

Equation?

Back 3

For a gas-liquid interface, gas will continue to dissolve in a liquid until partial pressure of dissolved gas = partial pressure of gas in gas phase.

Pressure = [ ]gas/solubility coefficient

Front 4

How does partial pressure of a gas differ based on solubility?

Back 4

A more soluble gas will exert less partial presure per molecule of dissolved gas, and therefore more molecs will dissolve before system reaches equilibrium and difusion ceases.

Front 5

CO2 vs O2: solubility

Back 5

CO2 is ~20x more soluble than oxygen, so will be higher [CO2] than oxygen at a given partial pressure

Front 6

Beginning with the alveolus and ending with a RBC, list the barriers oxygen must diffuse across.

Back 6

Surfactant
Alveolar Epithelium
BM
Interstitium
BM
Capillary Endothelium
RBC

Front 7

What does Fick's Law state?

Equation? Define variables.

Back 7

Flux (diffusion) of a gas across a membrane =
(SA x Diffusion Coeff x delaP)/thickness

where diffusion coeff = Gas solubility/sq(molecular wt)

Front 8

What is the main impediment to diffusion for O2/CO2?

Back 8

Water

Front 9

How does solubility affect rate of diffusion?

Back 9

Higher solubility-->higher rate of diffusion

Front 10

How does gas molecular weight affect rate of diffusion?

Back 10

Gas MW = gas size
Lower MW (smaller gas)-->greater kinetic velocity
Thus, greater rate of diffusion

Front 11

PO2: alveolus vs capillary

Back 11

PO2 alveolus> PO2 capillary; helps drive O2 into capillary

Front 12

Effect of Hg on PO2.

Back 12

Once oxygen bound to Hg, it exerts no partial pressure--creates O2 [ ] gradient

Front 13

What is the main driving force of oxygen diffusion between alveolus and capillary?

Back 13

partial pressure difference; NOT CONCENTRATION

Front 14

What the normal transit time of blood through an alveolar capillary?

I sthis enough time for oxygen partial pressure equilibration?

Back 14

Blood takes 0.75 sec to travel through alveolar capillary.

O2 partial pressure equilibration occurs at about 0.25 sec.

Thus 0.75 sec is enough time for O2 to saturate Hg.

Front 15

What is the physiologic shunt and why does it exist?

Back 15

Arterial pO2 is not the same as alveolar pO2.

This alveolar-arterial gradient is due to small amounts of blood that enter left heart without being oxygenated in lungs (shunt or venous admixture)--mostly from bronchial circulation and thebesian veins (drain coronary circulation)

Front 16

Partial pressure of O2 in alveolus?

Back 16

100 mmHg

Front 17

If pcO2 readily equilibrates with pAO2, how can blood O2 delivery increase?

Back 17

Increase perfusion by pumping additional blood past alveolus

Front 18

Diffusion-Limited vs Perfusion-Limited Gases:
General
Examples

Back 18

Diffusion-limited gas: CO
CO is perfusion-limited bc Hg binds all CO and there is NO partial pressure of CO in plasma. Thus, CO continues to diffuse into capillary.

N2O is a perfusion-limited gas (doesn't bind with Hg). Partial pressure of N2O in capillary rapidly reaches equilibrium with alveolus.

Front 19

Is oxygen a diffusion-limited or perfusion-limited gas? Why?

Back 19

Oxygen is perfusion-limited under NORMAL conditions

With extreme exercise, there's decreased transit time, capillary blood may no thave time to fully equilibrate and it may be diffusion-limited (this is unusual)

Front 20

CO2 vs O2:
Diffusion Rates
Equilibration time

Back 20

CO2 more soluble than O2, will diffuse more rapidly despite lower partial pressure gradient

CO2 must be formed from bicarbonate ion, which takes time, thus increasing total time req'd for equilibration

Front 21

What is diffusion capacity?

Equation?

Gases used clinically?

Back 21

Diffusion capacity = Flux/Pressure Difference

where pressure diff is between alveolus and capillary

For CO; pcapillary ~0, so equation:
Diffusion Capacity = Uptake of CO/pAlveoral CO

Oxygen diffusion gradient changes with time and is diff to measure

But all CO diffused in blood binds Hg and exerts no partial pressure (CO is easier to measure)

Front 22

Diffusion capacity equations take both membrane diffusing capacity and __________ into account.

Back 22

Displacement of O2 from Hg by CO ("Hemoglobin reaction time")

Front 23

What 3 factors affect DLCO?

Back 23

DLCO = Diffusing Capacity of the Lung for CO

Factors affecting:
membrane SA
alveolocapillary thickness
gas uptake by Hg

Front 24

Effect of lung volume and height on DLCO.

Back 24

If have total lung capacity, will have DLCO higher than at FRC.

Height is directly related to lung volume. Tall person will have higher DLCO than short person.

Front 25

Effect of emphysema on DLCO.

Back 25

Low DLCO due to dec'd SA

Front 26

Effect of pulmonary fibrosis on DLCO.

Back 26

Pulmonary fibrosis increases the distance O2 must diffuse between alveolus and capillary; thus, decreases DLCO.

Front 27

Effect of anemia on DLCO.

Back 27

Anemia-->low hg concentration-->reduced rate of CO transfer, decreasing DLCO

Front 28

Effect of exercise on DLCO.

Back 28

Mod exercise will inc DLCO by recruiting underperfused pulm capillaries, increasing SA for gas exchange and pulm cap blood volume.

Front 29

Effect of age on DLCO.

Back 29

Increasing age is correlated with DEC'D diffusing capacity

This is independent of effects of age on lung volume and height.