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Pulmonary > PHYS: Gas Exchange > Flashcards

PHYS: Gas Exchange Flashcards

1
Q

What is RQ?

A

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

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2
Q

The respiratory quotient depends on what?

A

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

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3
Q

How do you calculate partial pressure of a gas?

A

Atmospheric pressure X fraction of gas molecules in the dry air

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4
Q

What is the partial pressure of oxygen in air?

A

159 mmHg

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5
Q

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

A

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

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6
Q

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

A

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

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7
Q

Diffusion of gas across a membrane depends on what factors?

A

pressure difference
area
membrane thickness

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8
Q

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

A

CO2 is 20 times faster at diffusing than O2

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9
Q

What are the Pco2 and Po2 at the alveoli?

A 
Pco2= 40 mmHg
Po2= 105 mmHg
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10
Q

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

A 
Pco2= 40 mmHg
Po2= 100 mmHg (won't equilibrate due to shunts and slower diffusion)
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11
Q

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

A 
Pco2= 46 mmHg
Po2= 40 mmHg
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12
Q

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

A

CO2 production/ alveolar ventilation

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13
Q

Increased ventilation will do what to PAco2?

A

decrease it (fresh inspired air dilutes the gas)

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14
Q

Increased metabolism will do what to PAco2?

A

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

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15
Q

What is the alveolar gas equation?

A

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

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16
Q

What is hypoxemia?

A

lower than normal (100 mmHg) arterial Po2

17
Q

What is the A-a gradient?

A

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)

18
Q

What is Pao2/Fio2?

A

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

19
Q

What is the Pao2/Fio2 in ARDS?

A

less than 100 if severe

20
Q

What is hypoxia?

A

decrease in O2 delivery to or utilizaiton by dissues

21
Q

What is hypercapnia?

A

higher than normal arterial Pco2 (normal is 40)

22
Q

What is the most common cause of hypercapnia?

A

low alveolar ventilation

23
Q

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

A

true!

24
Q

Diffusion of oxygen and CO2 is described as what type?

A

Perfusion-limited (blood flow determines amount that diffuses)

25
Q

Diffusion of carbon monoxide is described as what type?

A

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

26
Q

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

A

1) Oxygen is physically dissolved in the blood

2) Oxygen (4 molecules) is bound to Hb

27
Q

Oxygen binds to what form of heme?

A

Ferrous (2+) iron portion

28
Q

What is methemoglobin?

A

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

29
Q

Why does fetal Hb have a higher affinity for oxygen?

A

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

30
Q

What is cooperativity in relation to the Hb dissociation curve?

A

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

31
Q

Low Hb saturation in surface capillaries causes what phenomenon?

A

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

32
Q

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

A

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

33
Q

What causes a right shift in the Hb dissociation curve?

A 
DAT ACE
2,3- DPG
Altitude
Temperature
Acid/Anemia
CO2
Exercise
34
Q

What causes a left shift in the Hb dissociation curve?

A 
low 2,3-DPG
low temperature
Basic environment
Low CO2
Fetal Hb
35
Q

A right shift is a _____ in affinity.

A

decrease (good for unloading)

36
Q

A left shift is a _____ in affinity.

A

increase

37
Q

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

A

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

38
Q

What factors can affect the oxygen content of blood?

A

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

Pulmonary (34 decks)

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