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FSM Pulmonary > Ventilation/Diffusion/Gas Transport > Flashcards

Ventilation/Diffusion/Gas Transport Flashcards

1
Q

What is the conventional way fractional gas concentrations are reported?

A

As though there were no water present Fg = Pg/(Pb-Ph2o)

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2
Q

What does the pressure of water vapor in the airways depend on?

A

Temperature

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3
Q

What is convention for expressing volumes of ventilated gas (ex: TV)?

A

BTPS (body temp, ambient pressure, saturated with water vapor)

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4
Q

What is the convention for expressing metabolic rates (O2 consumption, CO2 production)?

A

STPD (because volumes at STPD direct relate to moles)

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5
Q

What is Henry’s Law?

A

C(gas) = K*P(gas)

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6
Q

What does K indicate in Henry’s Law?

A

Solubility (depends on specific gas, solvent, and temperature)

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7
Q

How do the solubilities of O2 and CO2 compare?

A

CO2 is MUCH more soluble in blood than O2

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8
Q

How does diffusion occur within a medium vs between different media?

A

In a medium - down concentration gradient Between media - down partial pressure gradient

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9
Q

Why does convection occur?

A

Breathing makes the air (medium) move in a circulatory way, contributing to gas exchange and diffusion.

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10
Q

What is minute ventilation (V dot)?

A

Amount of air inspired/minute (V dot I) or expired/minute (V dot E)

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11
Q

How do you calculate minute ventilation?

A

VT x breathing frequency Normal: 500 mL x 15/min = 7.5 L/min

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12
Q

Where does the last air inspired in each tidal breath go?

A

It stays in the anatomic dead space (conducting airways)

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13
Q

How do you calculate alveolar ventilation?

A

f x (VT-VD) VT>VD, usually VT = 3 X VD

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14
Q

What is the effect of decreasing respiratory frequency on alveolar ventilation?

A

It will increase V dot A (this advantage is limited by mechanical factors, etc though)

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15
Q

What is alveolar dead space?

A

Alveolar gas volume that is ventilated but not effectively perfused, so it does not participate in gas exchange. Reasons - hydrostatic failure, PE, lung injury (ventilation of non-vascular air space), external obstruction of pulmonary circulation (Ex: tumor).

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16
Q

What is the physiologic dead space?

A

The total volume of inhaled gas that doesn’t participate in gas exchange - sum of anatomic + alveolar dead space. In health, anatomic = physiologic dead space.

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17
Q

What is the respiratory quotient?

A

R = V dot CO2/V dot O2

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18
Q

What does RQ depend on?

A

Diet and metabolism

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19
Q

Rank these diets from highest to lowest RQ: lipid, carbohydrate, protein

A

Carbohydrate (RQ = 1) > Protein (RQ = 0.83) > Lipid (RQ = 0.7)

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20
Q

What is a normal RQ?

A

0.8

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21
Q

What are two reasons that alveolar air is different from ambient air?

A

1) Water vapor 2) CO2 from circulation

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22
Q

What is the partial pressure of water vapor at 37 C (body temperature)?

A

47 mm Hg

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23
Q

Why can we say that inspired O2 = alveolar O2 and alveolar CO2?

A

1) No net exchange of N2 by body (partial P equation becomes PIO2 + PICO2 = PAO2 + PACO2) 2) Basically no CO2 in room air (PICO2 = 0)

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24
Q

What is the normal range for PAO2?

A

90-105 mm Hg

25
Q

What is the consequence of having an RQ<1?

A

Expired volume is less than the inspired volume. (This is why we must divide PACO2 by RQ in the alveolar gas equation)

26
Q

What is the relationship between alveolar ventilation (V dot A) and PACO2?

A

Inversely hyperbolically related (with constant metabolic rate). However, ventilation increases proportionally with metabolic rate (ex: with exercise) which keeps PACO2 nearly constant.

27
Q

How do we define hyperventilation and hypoventilation?

A

Hyperventilation - more alveolar ventilation than needed to maintain normal PCO2

HypOventilation - Less alveolar ventilation than needed to maintain normal PCO2

28
Q

What is the hallmark of hyperventilation? Hypoventilation?

A

Hyperventilation: hypocapnia

Hypoventilation: hypercapnia

*need to know metabolic rate to define these though

29
Q

What is hyperpnea?

A

Appropriate increase in alveolar ventilation with increased metabolic rate to maintain constant PaCO2.

30
Q

What is hypopnea?

A

Appropriate decrease in alveolar ventilation with decreased metabolic rate to maintain constant PaCO2.

31
Q

What is the relationship between alveolar ventilation and PAO2?

A

Hyperbolically proportional

32
Q

What does venous admixture mean?

A

Mixing of shunted, non-oxygenated blood with normal oxygenated blood

33
Q

What does the rate of gas diffusion depend on?

A

Proportional to area and pressure gradient, inversely proportional to thickness.

Also depends on the diffusion coefficient D, which is proportional to gas solubility and inversely proportional to molecular weight.

34
Q

What influences the diffusion path for O2 between the lung and blood?

A

Normally none of the first 4 pose significant barriers (path worsens):

Crossing gas space within alveolus (emphysema, loss of lung tissue

Crossing alveolar-capillary membrane (thickening from fibrosis)’

Through plasma from capillary wall into RBCs

Across RBC membrane into cell

O2 combining with Hb ** reaction rate is signicant

35
Q

What limits the rate of O2 transfer from alveolar gas into blood?

A

Reaction rate of O2 combining with Hb.

36
Q

What is the normal transit time for blood in the pulmonary capillaries (at rest)?

A

0.75 sec

37
Q

What type of gas transfer exchange does CO follow?

A

Diffusion limited

38
Q

Why does a rise in CO concentration in the blood only increase its partial pressure slowly?

A

The effective solubility (capacitance) is very high because of its tight binding with Hb, and there is normally not any baseline CO present.

Partial P = concentration/capacitance

39
Q

What does the gas transfer rate of diffusion limited gas depend on?

A

The diffusional characteristics of the membrane and the gas

40
Q

How does increasing blood flow rate affect diffusion limited gas transfer?

A

It does not.

41
Q

In general, how does partial pressure correlate with gas solubility?

A

Dissolving more soluble gases raise partial pressure slowly (they need more gas dissolved to raise partial P)

Dissolving insoluble gases can raise partial P very quickly.

(Partial pressure = concentration/capacitance, capacitance = effective solubility)

42
Q

What type of gas transfer exchange does N2O follow?

A

Perfusion limited

43
Q

What determines gas exchange rate for perfusion limited gases?

A

The rate of blood flow. The partial pressure of such gases increases very fast, so it mainly depends on perfusion rate.

44
Q

What type of gas transfer exchange does O2 follow?

A

Perfusion limited (less rapid than N2O though)

45
Q

What is the diffusing capacity (DL) of the lung?

A

Rate of gas transfer/pressure gradient across alveolar-capillary membrane.

Summarizes both diffusion through blood-gas barrier and the chemical reactions of O2 and CO2 in the RBCs.

46
Q

What is the equational analogue of resistance to diffusion in the lung?

A

1/DL

47
Q

What limits the rate of CO2 exchange (preventing it from being super fast)?

A

Chemical reactions of CO2

1) formation of bicarbonate (HCO3-)
2) formation of carbamino compounds with blood proteins (esp Hb)

48
Q

What is the solubility of O2 in blood?

A

0.003 mL/100 mL blood/mm Hg

49
Q

What is the oxygen capacity?

A

Maximum amount of oxygen that can bind Hb

50
Q

What is the p50 of Hb?

A

PO2 when 50% O2 capacity is bound to Hb (indicates affinity of Hb for O2). Normal is about 27 mm Hg.

51
Q

What does a low P50 for the Hb-O2 curve mean about the affinity of Hb for O2?

A

High affinity.

52
Q

How does a right shift in the Hb-O2 curve affect P50?

A

P50 increases

53
Q

What is the percent saturation (SO2) equation?

A

SO2 = (O2 content/O2 capacity) * 100

54
Q

What are three things that cause a right shift of the Hb-O2 curve?

A

Increased temperature, decreased pH/increased PCO2, increased 2,3-DPG

55
Q

What is the expression for O2 delivery to tissues?

A

O2 delivery = arterial O2 concentration x blood flow

56
Q

What are the forms of CO2 in the blood?

A

1) dissolved CO2
2) bicarbonate
3) carbamino compounds

57
Q

What enzyme catalyzes the conversion of CO2 to H2CO3?

A

Carbonic anhydrase

58
Q
A

FSM Pulmonary (3 decks)

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