Gas Diffusion

Question 1

Select the statement that best describes the relative solubilities of O2 and CO2

Answer 1

CO2 is 20x more soluble than O2

CO2 gets through membrane more easily.

Question 2

What happens if the stimulation to breathe is low, such as having pain in the chest/ribcage?

Answer 2

CO2 would not get out of the body as much. Can lead to alveolar disturbance.

Question 3

Hypoxemia caused by diffusion impairment is typically associated with:

Answer 3

A-aDO2 that is increased.

O2 is not getting from alveolus into the capillary blood

FiO2 normal, PiO2 normal, PAO2 WNL, pathway from there to PaO2 is not normal

Question 4

Is A-aDO2 able to decrease?

Answer 4

No

Question 5

Which of the below factors, when increased, would facilitate diffusion?

Answer 5

Gas partial pressure gradient

Surface area for gas diffusion (more wider)

Gas solubility (CO2>O2 more readably)

Question 6

What is the correct shorthand pathway for O2 movement from the atmosphere to arterial blood?

Answer 6

FiO2 → PiO2 → PAO2 → PaO2

Question 7

What specific mechanism moves O2 from the alveolus PAO2 into the capillary blood PaO2?

Answer 7

Gas diffusion across the alveolar septa

Question 8

In which direction does CO2 removal occur?

Answer 8

It moves from the capillary blood into the alveolus

double check with histology lab

Question 9

Under normal conditions, how quickly do O2 and CO2 equilibrate across the alveolar septa?

Answer 9

Before the blood traverses half of the alveolar capillary.

Question 10

Define the variables in the oxygen pathway: FiO2, PAO2, and PaO2.

Answer 10

FiO2: fraction of inspired air

PAO2: Partial pressure of oxygen in the alveolus

PaO2: Partial pressure of oxygen in the arterial blood.

Question 11

What is considered the primary clinical problem affecting diffusion rate?

Answer 11

Barrier (membrane) thickness.

Question 12

Which factor is most commonly manipulated as a clinical treatment for diffusion issues?

Answer 12

The Gas partial pressure gradient (e.g., by giving supplemental oxygen).

Question 13

How does an incentive spirometer (common in human medicine) help improve diffusion?

Answer 13

It helps increase/maintain the Surface area for gas diffusion by keeping alveoli open.

Question 14

Why is membrane thickness such a common clinical issue in veterinary medicine?

Answer 14

Conditions like pulmonary edema, pneumonia, and fibrosis all increase the thickness of the barrier, slowing down oxygen exchange.

Question 15

What is the mathematical equation used to determine the Rate of Diffusion?

Answer 15

Rate of diffusion = {D × surface area × (partial pressure difference)} /
membrane thickness

Determinants in the numerator enhance diffusion and those in the denominator impede it.

Question 16

Which three factors are in the numerator (meaning increasing them enhances diffusion)?

Answer 16

1. Gas solubility (D)
2. Surface area
3. Partial pressure gradient

Question 17

Which factor is in the denominator (meaning increasing it impairs diffusion)?

Answer 17

Membrane (barrier) thickness.

Question 18

How does increasing the partial pressure gradient affect gas exchange?

Answer 18

It facilitates/enhances diffusion by “pushing” more gas across the barrier.

Question 19

What happens to the rate of diffusion if the barrier thickness increases (e.g., due to fibrosis)?

Answer 19

The rate of diffusion decreases (it is an inverse relationship).

Question 20

True or False: A larger surface area for gas diffusion leads to a lower rate of diffusion

Answer 20

False.

Increasing surface area enhances the rate of diffusion.

Question 21

What are the four primary factors that determine the rate of diffusion across the alveolar septa?

Answer 21

1. Gas solubility coefficient (D)
2. Surface area
3. Gas partial pressure gradient
4. Barrier (membrane) thickness

Question 22

If a patient has a reduced number of functional alveoli, which specific factor is being decreased?

Answer 22

Surface area for gas diffusion.

Question 23

Which factor is being manipulated when you move a patient into an oxygen cage?

Answer 23

The Gas partial pressure gradient (by increasing the concentration of inspired oxygen).

Question 24

True or False: A gas with a high solubility coefficient (D) will diffuse more slowly than a gas with a low solubility coefficient.

Answer 24

False.

A higher solubility coefficient increases the rate of diffusion.

Question 25

How much more soluble is CO2 compared to O2?

Answer 25

Approximately 20 times more soluble.

Question 26

Which alveolar gas diffuses most readily across the septa?

Answer 26

CO2

Question 27

What is the primary functional role of Nitrogen (N2) in the alveolus?

Answer 27

It diffuses least readily, allowing it to stay in the alveolus and prevent atelectasis (alveolar collapse).

Question 28

When a patient has a diffusion impairment, which gas is impacted first/most?

Answer 28

Oxygen (O2).

Question 29

Why is CO2 levels often normal or even low in a patient with a diffusion barrier?

Answer 29

Because CO2 is so highly soluble that it can still cross a thickened membrane, while O2 gets "stuck."

Question 30

What happens to A-aDO2 (Alveolar-arterial O2 difference) during diffusion impairment?

Answer 30

It increases.

Question 31

What does an increased A-aDO2 physically represents in the lungs?

Answer 31

It means O2 is present in the alveolus but is failing to cross into the capillary blood.

Question 32

What is a typical reference range for A-aDO2, and what might a pathological value look like?

Answer 32

Reference range is <20 mmHg; a pathological value could be significantly higher (e.g., 55.95 mmHg).

Question 33

When are clinical symptoms of diffusion impairment most likely to appear?

Answer 33

During exertion or exercise.

Question 34

Why might a patient be asymptomatic at rest but have dyspnea during light exercise?

Answer 34

At rest, blood moves slowly enough to equilibrate; during exercise, blood moves too fast to cross the thickened barrier.

Question 35

What is the typical compensatory response to the hypoxemia caused by diffusion impairment?

Answer 35

Compensatory hyperventilation (which leads to a decreased PaCO2).

Question 36

Why does hypoxemia from diffusion impairment respond well to supplemental O2?

Answer 36

It increases the FiO2, which creates a steeper pressure gradient to "push" oxygen across the barrier.

Question 37

Predict the primary impact on diffusion: Inflammation

Answer 37

causes increase in membrane thickness

Question 38

Predict the primary impact on diffusion: Interstitial Edema

Answer 38

causes increase in membrane thickness

Question 39

Predict the primary impact on diffusion: Fibrosis

Answer 39

causes increase in membrane thickness

Question 40

Predict the primary impact on diffusion: Chest pain

Answer 40

causes decrease in surface area via alveolar hypoventilation +/-

Question 41

Predict the primary impact on diffusion: Anesthesia

Answer 41

causes decrease in surface area via alveolar hypoventilation +/-

Question 42

Predict the primary impact on diffusion: Obesity

Answer 42

causes decrease in surface area via alveolar hypoventilation

Question 43

Predict the primary impact on diffusion: Low PiO2

Answer 43

causes decrease in Gas partial pressure gradient

Question 44

What is the clinical definition of Alveolar Hypoventilation?

Answer 44

When CO2 cannot get out of the body at the same rate the body is producing it.

Question 45

Which gas is used to define ventilation clinically?

Answer 45

CO2

Question 46

In which two conditions is the AaDO2 typically NORMAL?

Answer 46

1. Low PiO2 (e.g., high altitude) 2. Alveolar Hypoventilation

Question 47

List three conditions where the A-aDO2 is ABNORMAL (Increased).

Answer 47

1. Diffusion Impairment 2. V/Q Mismatch 3. Right-to-Left Shunt

Question 48

How much of the capillary distance does an RBC usually travel before gas exchange is complete?

Answer 48

Within the first third 1/3 of the traversal.

Question 49

What are the two primary reasons a patient would undergo Compensatory Hyperventilation?

Answer 49

1. To compensate for Metabolic Acidosis 2. To compensate for Hypoxemia

Question 50

List four specific causes of hypoxemia that trigger hyperventilation.

Answer 50

1. Low PiO2 2. Diffusion impairment 3. Low V/Q mismatch 4. Right-to-Left shunt

Question 51

Why might PaCO2 fluctuate between low, normal, and high over time in a struggling patient?

Answer 51

Because hyperventilation requires work and may not be sustainable; the patient may eventually tire out.

Question 52

When compensating, do patients tend to change Tidal Volume (Vt) or Frequency (f) more?

Answer 52

They tend to change Tidal Volume (Vt) more than frequency.

Question 53

What two physical factors can impede a patient's ability to hyperventilate?

Answer 53

Stiff lungs (decreased compliance) and Obesity.

Question 54

Under normal conditions O2 and CO2 both equilibrate across the alveolar septa before blood traverses half the alveolar capillary: True or False?

Answer 54

True

Question 55

Diffusion impairment is the most common cause of hypoxemia: True or False?

Answer 55

False It is uncommon.

Question 56

Diffusion abnormalities impair the diffusion of O2 more than they impair the diffusion of CO2: True or False?

Answer 56

True

Question 57

A history of no symptoms at rest and dyspnea induced by light exercise is suggestive of which cause of hypoxemia?

Answer 57

Diffusion impairment

Question 58

Predict the primary impact on diffusion: Alveolar Edema

Answer 58

Surface area would decrease