PHYS: Gas Exchange

Question 1

What is RQ?

Answer 1

respiratory quotient: ratio of CO2 produced to O2 consumed (normally around 0.8)

Question 2

The respiratory quotient depends on what?

Answer 2

What we eat and burn (RQ is 1 for Carbs, and .7 for Fat)

Question 3

How do you calculate partial pressure of a gas?

Answer 3

Atmospheric pressure X fraction of gas molecules in the dry air

Question 4

What is the partial pressure of oxygen in air?

Answer 4

159 mmHg

Question 5

What happens to the partial pressure of oxygen if it is inspired?

Answer 5

it decreases to around 150 mmHg due to humidification (must subtract out water vapor)

Question 6

How is concentration of a gas related to it partial pressure?

Answer 6

concentration (amount dissolved) is equal to partial pressure X solubility

Question 7

Diffusion of gas across a membrane depends on what factors?

Answer 7

pressure difference
area
membrane thickness

Question 8

Which is better at diffusing in blood and tissue, CO2 or O2?

Answer 8

CO2 is 20 times faster at diffusing than O2

Question 9

What are the Pco2 and Po2 at the alveoli?

Answer 9

Pco2= 40 mmHg
Po2= 105 mmHg

Question 10

What are the Pco2 and Po2 at the lung capillary after diffusion?

Answer 10

Pco2= 40 mmHg
Po2= 100 mmHg (won't equilibrate due to shunts and slower diffusion)

Question 11

What are the Pco2 and Po2 in the systemic veins after diffusion into tissue?

Answer 11

Pco2= 46 mmHg
Po2= 40 mmHg

Question 12

Alveolar partial pressure of oxygen is determined by the ratio of what two values?

Answer 12

CO2 production/ alveolar ventilation

Question 13

Increased ventilation will do what to PAco2?

Answer 13

decrease it (fresh inspired air dilutes the gas)

Question 14

Increased metabolism will do what to PAco2?

Answer 14

increase CO2 production so increase PAco2 (more CO2 enters alveoli from blood per unit time)

Question 15

What is the alveolar gas equation?

Answer 15

PAo2= PIo2 - PAco2/ (CO2 prduction/O2 consumption)

Question 16

What is hypoxemia?

Answer 16

lower than normal (100 mmHg) arterial Po2

Question 17

What is the A-a gradient?

Answer 17

It is the difference between Po2 in alveolar gas and arterial blood (tells if O2 has equilibrated between the two and is useful for examining causes of hypoxemia)

Question 18

What is Pao2/Fio2?

Answer 18

The ratio of arterial Po2 to the fraction of inspired oxygen (useful for measuring acute lung injury–normal is 476 mmHg)

Question 19

What is the Pao2/Fio2 in ARDS?

Answer 19

less than 100 if severe

Question 20

What is hypoxia?

Answer 20

decrease in O2 delivery to or utilizaiton by dissues

Question 21

What is hypercapnia?

Answer 21

higher than normal arterial Pco2 (normal is 40)

Question 22

What is the most common cause of hypercapnia?

Answer 22

low alveolar ventilation

Question 23

True or false: virtually all gas exchange is completed in the initial region of the pulmonary capillary.

Answer 23

true!

Question 24

Diffusion of oxygen and CO2 is described as what type?

Answer 24

Perfusion-limited (blood flow determines amount that diffuses)

Question 25

Diffusion of carbon monoxide is described as what type?

Answer 25

Diffusion-limited (extremely soluble in blood, so it doesn't matter how much blood is there)

Question 26

What are the two mechanisms for oxygen transport in the blood?

Answer 26

1) Oxygen is physically dissolved in the blood | 2) Oxygen (4 molecules) is bound to Hb

Question 27

Oxygen binds to what form of heme?

Answer 27

Ferrous (2+) iron portion

Question 28

What is methemoglobin?

Answer 28

oxidized heme with iron in the ferric (3+) state, so it cannot bind to oxygen

Question 29

Why does fetal Hb have a higher affinity for oxygen?

Answer 29

it has 2 alpha and 2 gamma subunits (adults have 2 alpha and 2 beta)

Question 30

What is cooperativity in relation to the Hb dissociation curve?

Answer 30

binding of 1 oxygen to heme increases the affinity for other molecules to the remaining spots (gives sigmoidal shape to curve)

Question 31

Low Hb saturation in surface capillaries causes what phenomenon?

Answer 31

cyanosis (bluing of lips, ears, nails, tongue)

Question 32

True or false: all oxygen in the blood contributes to the partial pressure of oxygen.

Answer 32

FALSE: only dissolved, free oxygen (not oxygen bound to hemoglobin)

Question 33

What causes a right shift in the Hb dissociation curve?

Answer 33

``` DAT ACE 2,3- DPG Altitude Temperature Acid/Anemia CO2 Exercise ```

Question 34

What causes a left shift in the Hb dissociation curve?

Answer 34

``` low 2,3-DPG low temperature Basic environment Low CO2 Fetal Hb ```

Question 35

A right shift is a _____ in affinity.

Answer 35

decrease (good for unloading)

Question 36

A left shift is a _____ in affinity.

Answer 36

increase

Question 37

How does 2,3-DPG decrease Hb affinity for O2?

Answer 37

it binds strongly to deoxygenated Hb and lowers its affinity for oxygen

Question 38

What factors can affect the oxygen content of blood?

Answer 38

carbon monoxide poisoning (binds strongly to Hb and decreases maximum O2 capacity as well as making O2 unloading more difficult