Gas transport in the Airway Flashcards Preview

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Flashcards in Gas transport in the Airway Deck (62):
1

what has to be considered when calculating air PIO2 (partial pressure of inspired air)

1) total pressure of inhaled air = Pa

2) sum of partial pressures of each gas in air = PB

3) each gas makes up certain percentage (dry air)
21% O2
0.03% CO2
79% N2

4) air immediately saturated with water when enter airway so water vapor pressure subtract from barometricP = 47 Torr @ 37C

2

Define PaO2

Normal value at sea level
Normal value at Denver

partial pressure of arterial O2

partial pressure of O2 in blood dissolved or bound to Hb in equilibrium with O2 in air

PaO2 = 90-100 Torr
PaO2 Denver = 80-85 Torr

3

air becomes ___ when it enters airway

consequences on water vapor pressure

saturated

so must subtract water vapor pressure from barometric pressure

4

what is equation for air PIO2 (Dalton's Law)
**** MEMORIZE

PIO2 = (PB - PH2O) x FO2

PIO2 = (PB - 47 Torr) x 0.21

5

what is partial pressure of water vapor

what is PB typically

47 torr

720 at sea level
620 at Denver

6

does partial pressure of water vapor vary with altitudes

no constant

7

does PB vapor vary with altitudes

does PIO2 vary with altitude

YES
decr at higher altitudes

8

equation for PB

PB = PIO2 + PIN2 + PICO2 + PIH2O

9

calculate PIO2 if patient breathing 100%

Use FO2 = 100%
PB = 760 Torr

PIO2 = 713 Torr

10

a

a

11

define respiratory exchange ratio in words

ratio of amount of CO2 generated per amount of O2 consumed

12

equation for respiratory exchange ratio

R = V(CO2) / V(O2)

13

why is respiratory exchange ratio significant

exchange of CO2 for O2 NOT ALWAYS 1:1

because metabolic reactions consume more O2 compared to CO2

carbs: R = 1.1
fats: R = 0.7
avg diet: R = 0.8

14

what are typical R values for
carbs
fats
avg diet

carbs: R = 1.1
fats: R = 0.7
avg diet: R = 0.8

15

what is factored into the calculation of alveolar PAO2

1) exchange of O2 for CO2 in alveoli based on R

16

when R decr with heavy fat diet, how does PAO2 change

substantial decrease

based on PAO2 = PIO2 - (PACO2/R)

17

when R decr with heavy fat diet, how does N2 change

increase in N2 as opposed to O2
because more N2 in air (4x more than O2)
so deficit created by low levels in CO2
made up by N2

18

equation for PAO2

PAO2 = PIO2 - (PACO2/R)

19

normal values in Denver for
PIO2
PACO2
R
R (if on 100% O2)

PIO2 = 120 Torr
PACO2 = 40 Torr
R = 0.8
R (if on 100% O2) = 1

20

difference between PACO2 and PaCO2

PACO2 = alveolar

PaCO2 = artery

21

normal values at sea level for
PIO2
PACO2
R
R (if on 100% O2)

PAO2

PIO2 = 150 Torr
PACO2 = 40 Torr
R = 0.8
R (if on 100% O2) = 1

PAO2 = 100 Torr

22

if patient is breathing 100% O2, why is R = 1

if breathe 100% O2, no N2

so deficit in CO2 made up by O2 and R drops out of equation and
PAO2 = PIO2 - PACO2

23

2 steps in CO2 removal

1) diffusion of CO2 from pulm capillaries to alveoli; THEREFORE PULM CAPILLARY EQUILIBRIUM WITH ALVEOLI CO2

2) CO2 transport from alveoli to the outside air.

24

what is rate limiting step between two steps of CO2 removal

why?

transport of CO2 to outside air (ventilation)

because diffusion of CO2 from blood to alveoli = assumed near instantaneous (FAST)

25

what does rate limiting step of CO2 removal depend on?

what does it affect?

step = transport of CO2 to outside air

depends on:
1) alveolar ventilation

affects
1) PACO2
2) PaC=O2

26

what is significance of change in alveolar ventilation on rate limiting step in CO2 removal?

decr alveolar ventilation
decr CO2 removal
incr PACO2

but other step, diffusion from blood to alveoli near instant so PaCO2 (artery) equilibrate with PACO2 (alveoli)

27

PaCO2 and PACO2 assumed to be ____

why?

equal

because rapid diffusion of CO2 from blood to alveoli

28

what do PaCO2 and PACO2 depend on?

amount of CO2 being produced relative to alveolar ventilation rate

29

alveolar ventilation equation ***MEMORIZE

PACO2 = PaCO2 = (VCO2dot/VAdot) x k
k = constant

VCO2 dot = Co2 production per minute
VAdot = alveolar ventilation per minute

30

what is ideal PaCO2

40 Torr

31

why do we care about having particular PaCO2 = 40 Torr

affects pH

32

define hypoventilation

Low VAdot and High PaCO2
Constant VCO2dot

--> incr PaCO2

33

normal value of PaCO2 in Denver with hypoventilation

> 40 Torr

34

Causes of hypoventilation

1) severe Obstructive diseases = because if mild-moderate obstructive disease, decr VAdot body has compensatory mechanism to maintain total ventilation to maintain normal PaCO2 and pH

2) restrictive diseases

3) metabolic alkalosis

4) CNS depression

35

define hyperventilation

High VAdot and Low PaCO2
Constant VCO2 dot

--> decr PaCO2

36

Causes of hyperventilation

1) high altitude - ventilating more to compensate for low enviorn O2, decr CO2

2) acute hypoxemia

3) metabolic acidosis

4) CNS stimulation

37

define hyperpnia

High VAdot and normal PaCO2

--> PaCO2 unchanged

38

Causes of hyperpnia

moderate exercise (incr CO2, incr VACO2dot, to match incr VAdot)

39

what is partial pressure of water vapor

what is PB typically

47 torr

720 at sea level
620 at Denver

40

does partial pressure of water vapor vary with altitudes

no constant

41

does PB vapor vary with altitudes

YES
decr at higher altitudes

42

difference between PAO2 and PaO2

A= alveoli

a = arterial

43

why does respiratory exchange occur

1) Air entry mainly N2 and O2

2) Air in alveolus also has N2 and O2 BUT ALSO HAS CO2 because pulm capillaries
feeding CO2 into alveolus

3) for total pressure of air in alveolus similar to air coming in, with incr CO2 in alveolus then less N2 and O2

4) therefore, alveolar O2 less than PIO2 because CO2 replaces and exchanges

44

define respiratory exchange ratio in words

ratio of amount of CO2 PRODUCED to amount of O2 CONSUMED in metabolic reactions

45

equation for respiratory exchange ratio

R = V(CO2) / V(O2)

46

why is respiratory exchange ratio significant
*** memorize R for normal diet

exchange of CO2 for O2 NOT ALWAYS 1:1

because metabolic reactions consume more O2 compared to CO2

avg diet: R = 0.8

47

what are typical R values for
carbs
fats
avg diet

carbs: R = 1.0
fats: R = 0.7
avg diet: R = 0.8

48

what is factored into the calculation of alveolar PAO2

1) exchange of O2 for CO2 in alveoli based on R

49

equation for PAO2 (alveolar GAS EQUATION)
**** MEMORIZE

PAO2 = PIO2 - (PACO2/R)

therefore, PAO2 less than PACO2 because more CO2 in alveolus

50

normal values in Denver for
PIO2
PACO2
R
R (if on 100% O2)

PIO2 = 120 Torr
PACO2 = 40 Torr
R = 0.8
R (if on 100% O2) = 1

51

difference between PACO2 and PaCO2

PACO2 = alveolar

PaCO2 = artery

52

PaCO2 and PACO2 assumed to be ____

why?

equal

because rapid diffusion of CO2 from blood to alveoli

53

what do PaCO2 and PACO2 depend on?

amount of CO2 being produced relative to alveolar ventilation rate

54

Path for O2 transport

1) O2 entry into lungs

2) entry into pulm capillaries

3) pulm capillaries diffuse into arterial blood

55

Is PaCO2 inversely related to alveolar ventilation?

if 50% drop in scoop-out rate or 50% decr in CO2 concentration, then you reach new equilibrium where CO2 concentration is doubled (50% drop in scoop out)

so now pull out 2 CO2 molec per scoop

56

What is PaCO2 if VAdot decr by 50%

PaCO2 = (VCO2dot) / (VAdot) x k

PaCO2 will double

57

General solution for change in VAdot

PaCO2(new) / PaCO2 (old) = VAdot (old) / VAdot (new)

58

why can we substituTe PACO2 for PaCO2

amount of CO2 essentially same because diffusion is RAPID

DECR IN PAO2 WITH CHANGE IN VENTILATION

59

Blood CO2 is ___ regulated by alveolar ventilation

directly

60

___ is directly regulated by alveolar ventilation

Blood CO2

61

Blood O2 is ___ regulated by alveolar ventilation via its effects on alveolar CO2

indirectly

62

___ is indirectly regulated by alveolar ventilation via its effects on alveolar CO2

Blood O2