Lecture 9/10: Gas Exchange

Question 1

What is the point of the lungs?

Answer 1

The point of the lungs is to bring ventilation and perfusion together.

Question 2

Does the anatomic deadspace participate in gas exchange?

Answer 2

No.

Question 3

What do conducting airways do?

Answer 3

1. Humidify the air 2. Conduct air

Question 4

How can we alter airway resistance?

Answer 4

Bronchoconstrict Bronchodilate.

Question 5

If resistance is ____, airflow slows down and takes more muscle effort to do.

Answer 5

high

Question 6

If resistance is ____, airflow is fast and easy.

Answer 6

low

Question 7

What controls the airway resistance?

Answer 7

Resistance

Directly related to:

• viscosity of whatever
• length of the tube -

Inversely related to:

• Radius of the tube (⁴)

R= 8nL/r⁴

Question 8

Changes in _____ can have the biggest effects on resistance?

Answer 8

Radius of the tube

Question 9

What controls the dilation and constriction of our bronchioles?

Answer 9

Smooth muscle

Question 10

Why do we want to change airway resistance?

Answer 10

So that we can send air to alveoli with a good blood supply

Question 11

What is alveolar ventilation?

Answer 11

The amount of air that reaches the alveoli.

Va= TD-V_DS

_{=tidal volume - volume of the dead space}

Question 12

Minute alveolar ventilation

What is the average?

Answer 12

Amount of air that reaches the alveoli per minute

Va*Frequency

4L/ minute is the average.

Question 13

What is perfusion (Q)?

Answer 13

Perfusion (Q) is the amount of blood delivered to the tissue/min.

Average is 5L blood/minute.

Question 14

Alveolar gas exchange depends on what?

Answer 14

J= SA*D* (P₁-P₂)/distance

Diffusion of gases:

Increases as surface area, diffusion coefficient and pressure gradient increases.

Decreases as the thickness of the wall increases.

Question 15

Are gas exchange of O2 and CO2 dependent on one another?

Answer 15

No.

They are independent of one another.

Question 16

In the lungs, does O2 trade places with CO2?

Answer 16

NOOOO.

Question 17

How much gas is exchanged (J) every minute?

Of O2 and CO2

Answer 17

250 mL of O₂ every minute.

200 mL of CO₂ every minute.

thus, they are not equal and not dependent on one another in the LUNGS. In the tissue, yes; they are.

Question 18

What factors the affect the diffusion of gas directly involve the structure of the alveolus?

Answer 18

1. Surface area

2. Distance (thickness of the alveolar wall)

They can be altered due to pathology.

Question 19

What is surface area referring to?

Answer 19

It corresponds with the number of alveoli in the lungs and the number of “open” pulmonary capillaries.

Question 20

Pt presents with COPD. What is causing this?

Answer 20

A decrease in surface area of the alveoli.

Question 21

What does the thickness of the alveolar barrier include?

Answer 21

1. Fluid layer

2. Alveolar epithelium

3. Interstitital space

4. Wall of the BV

Question 22

Usually, how big is the alveolar barrier?

Answer 22

0.6 microns.

Very small.

Question 23

Does diffusion distance change in normal conditions? Support your answer.

Answer 23

No, it does not.

It does change in pathological conditions.

For example, people who have interstitial lung disease have a increase in diffusion distance because collagen is depositied in the interstitial space.

Question 24

What does the diffusion coefficient (D) for each gas depend on?

Answer 24

1. Solubility of gas in water (CO2 is more soluble in water than O2)
2. Molecular weight of the gas (CO2 weighs more than O2)

Question 25

Which moves slower: **CO2 or O2**?

Answer 25

**CO2.** Its solubility counters its molecular weight, causing its diffusion coefficient to be 20x higher than O2.

Question 26

**Venous pressure of O2 and CO2 at the lungs:**

Answer 26

**P_vO2= 40 mmHg** **P_vCO2= 45 mmHg**

Question 27

**Partial pressure of O2 and CO2 in the alveoli**

Answer 27

**P_AO2= 104 mmHg** **P_ACO2= 40 mmHg**

Question 28

Pressure gradient of O2 at the lungs

Answer 28

**P1-P2=** **104-40** **=60mmHg** Thus, this favors the flow of oxygen into the capillaries, O2 needs a big pressure gradient because the diffusion coefficient is soooo low.

Question 29

Pressure gradient of CO2 at the lungs

Answer 29

**P1-P2=** **40-45** **=-5 mmHg**

Question 30

What happens during oxygen exchange at the alveolar capillary?

Answer 30

At the alveolar capillar, venous pressure of O2 is about 40 mmHg. Once the blood leaves the lungs (in the pulmonary vein) PO2 will be about 100 mmHg. Every RBC spends 0.75 seconds in a pulmonary capillary. It only takes .25 of a second for oxygen to go from 40 mmHg--\> 100 mmHg. Thus, iif something occured, the RBC would have a 0.5second safety margin in the capillary to reach equillibrium, before the RBC would leave.

Question 31

How does heavy excercise affect oxygen exchange at the alveoli?

Answer 31

However, during heavy excercise, a RBC spends 0.25 seconds in a pulmonary capillary (LESS time than a normal person) Thus, there is no safety margin and if something is wrong with the patient, the RBC may not spend enough time in the capillary to come to equillibrium. Thus, someone with lung disease will have difficulty working out.

Question 32

Will someone with lung disease have a difficult time doing normal activities?

Answer 32

No. Because the RBC in the alveolar capillary long enough to pick up one load of oxygen, allowing them to do normal things,

Question 33

How do we determine the diffusion capacity of the lung for oxygen (DL_O2)?

Answer 33

It is 21 mmO2/min/mmHg. It decreases as we go along the capillary because oxygen enters our capillaries.

Question 34

How can we measure the diffusion capacity in the lung for oxygen?

Answer 34

We can use small [] of carbon monoxide (CO). CO binds to Hb so tightly that it does not allow O2 to bind. Thus, the arterial Paco is 0mm Hg. Have the person breath in a single breath of air with a small amount of CO. We know the amount of CO inhaled. Measure CO that is in the breath, when they exhale. The difference is what diffused across the lung. There is a correction factor DL_O2= 1.23 \* DL_{CO Recognize what is normal or low. If low, SA is decreased, diffusion distance increased or the gradient is fucked up.}

Question 35

What happens during CO2 exchange at the lungs?

Answer 35

PCO2 in the pulmary capillaries is 45mmHg. PCO2 in the alveoli is 40 mmHg. PCO2 will come to equillibrium almost instantly. That being said, we have a HUGH "safety" margin or time before it leaves the RBC. Therefore, a person has to have an extensive lung disease before they have a problem with CO2 retention.

Question 36

What is D_{LCO2 at rest}

Answer 36

At rest, D_LCO2 at rest is aboout ~400ml CO2/min/mmHg. **This is the 20 fold difference we were talking about!**

Question 37

How does the diffusion capacity for the lung for CO2 differ from O2?

Answer 37

**D_LCO2 \>\>\>\>\>\>\>\> D_LO2**

Question 38

How do we figure out D_LO2?

Answer 38

**D_LO2= 1.23 D_LCO**

Question 39

What is a consequence of the diffusion capacities of CO2 and O2?

Answer 39

A patient with lung disease will notice limitition to exercise/exertion first because their need for oxygen will exceed the ability of the lungs to allow for diffusion of oxygen. Change in PaO2 will occur earlier in the disease process because of its limitations to oxygen diffusion.

Question 40

What makes surfactant?

Answer 40

Type 2 pneumocytes

Question 41

Where does surface tension occur?

Answer 41

Air/water interface Note that the tissue is water.

Question 42

What does LaPlace's law say?

Answer 42

Pressure= 2T/r T=tension r= radius

Question 43

Alveoli are different sizes. In a large alveolus, the radius is large. Thus, what is the pressure?

Answer 43

Low.

Question 44

Alveoli are different sizes. In a small alveolus, the radius is small. Thus, what is the pressure?

Answer 44

High.

Question 45

Are the differences in pressure between alveoli bad, if there is no surfactant?

Answer 45

Yes. this would not be a problem if all alveoli were the same size. But they are not.

Question 46

What happens due to the difference in alveoli sizes if surfactant is absent?

Answer 46

Big alveolus=big radius= small pressure Little alveolus=little radius= high pressure. They share the same airway to air moves from high--\> low pressure. This is bad because the small alveoli gets smaller and the big alveoli gets bigger. No good news for the SA. As a result, we have poor lung inflation and our alveoli collapse.

Question 47

What will happen to a baby with collapsed alveoli?

Answer 47

Cyanotic Need to be put on 40% O2.

Question 48

WHAT DOES SURFACTANT DO?

Answer 48

Surfactant reduces surface tension in proportion to radius, decreasing the pressure in the small alveoli *\*\*\* more so in the smallest aveoli* than in the larger ones.

Question 49

What is surfactant made up of?

Answer 49

1. Phospholipids 2. Dipalitorylphosphatidylcholine 3. Surfactant protein- A, B\*, C, D B is the most important.

Question 50

Surfactant is stored in _______ but secreted into \_\_\_\_\_\_

Answer 50

**intracellular lamellar bodies** **alveolus**

Question 51

Small alveoli + surfactant=

Answer 51

Little tension Little radius **=SMALL PRESSURE**

Question 52

Big alveolus=

Answer 52

big radius= small pressure. Thus, surfactant eliminates the gradient for air to move down. and prevents the collapse. Thus, little and big alveoli can exist peacefully.