Phys- Diffusion

Question 1

The volume of oxygen in the lungs that is transported to the blood per unit time is equal to:

Answer 1

The volume of 02 consumption by cells in that same unit of time

Question 2

The rate of excretion of CO2 is equal to:

Answer 2

The rate of CO2 production by cells

Question 3

What is the respiratory quotient? Normal value?

Answer 3

CO2 production/O2 consumption

0.8

Question 4

The respiratory quotients varies with:

Answer 4

What we eat and burn

ex. RQ for carbs is 1, for protein is 0.8; takes more O2 from protein to make one CO2

Question 5

(T/F): The partial pressure of a gas depends upon the number of molecules in the mixture.

Answer 5

False - pressure exerted by each gas in a mixture is independent (Dalton’s Law)/gas molecules don’t usually interact

Question 6

Px =

Answer 6

Ptotal*Fx

Question 7

PIO2 =

Answer 7

(Patm - Pvapor)*FO2

(760-47)*.21 = 150mmHg

Question 8

Why must we account for water vapor when calculating the pressure of inspired O2?

Answer 8

Dry atmospheric air is humidified in the airway so water vapor “takes up room”, decreasing PIO2

Question 9

What happens to PIO2 in high altitude? Why?

Answer 9

Decreases; Patm decreases

Question 10

How do you calculate how much gas is dissolved in a mixture?

Answer 10

Cx = alpha*Px
(alpha = solubility)

Question 11

Normal solubility of O2? CO2?

Answer 11

0. 003

0. 07

Question 12

What is the implication of the different solubilities of O2 and CO2?

Answer 12

CO2 is 20x more soluble than O2, so at any given pressure, diffusion of CO2&raquo_space;» O2

Question 13

Gas flow =

Answer 13

A/xD(P1-P2)

Question 14

According to Fick’s Law, how does pulmonary edema cause hypoxemia?

Answer 14

Increased thickness

Question 15

According to Fick’s Law, how does emphysema cause hypoxemia?

Answer 15

Decreased surface area (obstruction)

Question 16

Where are the rates of diffusion of CO2 and O2 equal?

Answer 16

Alveoli - since it’s a gas dissolving into a gas, solubility doesn’t matter but the ratio of MW does, which is about the same for both

Question 17

Where are the rates of diffusion of CO2 and O2 different? How so?

Answer 17

Diffusion of CO2 and O2 between alveoli and pulmonary capillaries - since gas is dissolving into a liquid, solubility is important and CO2 is 20x more soluble than O2 so the rate of diffusion of CO2 from pulm capillaries is about 20x faster

Question 18

What is the normal PAO2? PACO2?

Answer 18

PAO2 = 105 mmHg
PACO2 = 40 mmHg

Question 19

What is the normal PaO2 in pulmonary vein/systemic arteries? PaCO2?

Answer 19

PaO2 = 100 mmHg
PaCO2 = 40 mmHg

Question 20

What is the normal PaO2 in pulmonary artery/systemic veins? PaCO2?

Answer 20

PaO2 = 40 mmHg
PaCO2 = 46 mmHg

Question 21

What drives the pressure gradient favoring O2 diffusion into cells?

Answer 21

Mitochondria utilize O2 so the PO2 is low in cells

Question 22

What is the alveolar ventilation equation?

Answer 22

PACO2 = VCO2/Valv
(The alveolar pressure of CO2 is directly proportional to the production of CO2 and inversely proportional to the alveolar ventilation)

Question 23

Why does alveolar ventilation equation not account for atmospheric CO2 breathed in?

Answer 23

There is virtually no CO2 in inspired air

Question 24

How do you calculate Palv?

Answer 24

Palv = (TV - Vds) * RR

Question 25

At constant CO2 production, PACO2 depends on:

Answer 25

Alveolar ventilation

Question 26

Increased alveolar ventilation = (increased/decreased) PACO2? Why?

Answer 26

Decreased; inspired air dilutes the CO2

Question 27

Increased CO2 production (increases/decreases) PACO2? Why?

Answer 27

Increases; more CO2 enters alveoli (mass action)

Question 28

What effect will increased metabolism have on the Valv/PACO2 curve?

Answer 28

Right shift = increased VCO2 will increase respiratory rate/Valv and increase amount of CO2 entering alveoli/PACO2

Question 29

If CO2 production is constant, what would happen if PACO2 increased from 40 mmHg to 80 mmHg during anesthesia?

Answer 29

Alveolar ventilation would also have to increase 2 fold to compensate
(turn down ventilator)

Question 30

Alveolar gas equation

Answer 30

PAO2 = PIO2 - PACO2/R

Question 31

The main drive for ventilation

Answer 31

PaCO2

central chemoreceptors very sensitive to changes in PaCO2

Question 32

Definition of hyperventilation

Answer 32

Ventilation in excess of that required metabolically

Question 33

Definition of hypoventilation

Answer 33

Ventilation that is inadequate for metabolic demand

Question 34

What is hypercapnia? Most common (general) cause?

Answer 34

Increased ARTERIAL CO2

Hypoventilation

Question 35

What is hypoxemia?

Answer 35

Decreased ARTERIAL O2

Question 36

What is hypoxia?

Answer 36

Decreased TISSUE O2

Question 37

What parameter is used to determine the cause of hypoxemia?

Answer 37

A-a gradient

Difference between PAO2 and PaO2

Question 38

Which can cause the other: hypoxia or hypoxemia?

Answer 38

Hypoxemia can cause hypoxia

Decreased O2 in alveoli can cause decreased O2 utilization

Question 39

O2 and CO2 transfer is _____-limited. Why?

Answer 39

Perfusion; blood takes 0.75s to traverse pulmonary capillary and only 0.25s to totally equilibrate with alveolar concentrations

Question 40

___ is a gas that is diffusion-limited. Why?

Answer 40

CO

It is highly soluble so the amount that can diffuse rather than the amount of blood limits gas transfer

Question 41

If gas is perfusion-limited, how is more O2 able to be delivered to tissue during exercise?

Answer 41

More capillaries open due to increased pulmonary vascular pressures

Question 42

What is the function of bronchial circulation?

Answer 42

Serves the conducting airways; doesn’t participate in gas exchange