Gas transport in the Airway

Question 1

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

Answer 1

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

Question 2

Define PaO2

Normal value at sea level

Normal value at Denver

Answer 2

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

Question 3

air becomes ___ when it enters airway

consequences on water vapor pressure

Answer 3

saturated

so must subtract water vapor pressure from barometric pressure

Question 4

what is equation for air PIO2 (Dalton’s Law)

** MEMORIZE

Answer 4

PIO2 = (PB - PH2O) x FO2

PIO2 = (PB - 47 Torr) x 0.21

Question 5

what is partial pressure of water vapor

what is PB typically

Answer 5

47 torr

720 at sea level
620 at Denver

Question 6

does partial pressure of water vapor vary with altitudes

Answer 6

no constant

Question 7

does PB vapor vary with altitudes

does PIO2 vary with altitude

Answer 7

YES

decr at higher altitudes

Question 8

equation for PB

Answer 8

PB = PIO2 + PIN2 + PICO2 + PIH2O

Question 9

calculate PIO2 if patient breathing 100%

Answer 9

Use FO2 = 100%
PB = 760 Torr

PIO2 = 713 Torr

Question 10

a

Answer 10

a

Question 11

define respiratory exchange ratio in words

Answer 11

ratio of amount of CO2 generated per amount of O2 consumed

Question 12

equation for respiratory exchange ratio

Answer 12

R = V(CO2) / V(O2)

Question 13

why is respiratory exchange ratio significant

Answer 13

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

Question 14

what are typical R values for
carbs
fats
avg diet

Answer 14

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

Question 15

what is factored into the calculation of alveolar PAO2

Answer 15

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

Question 16

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

Answer 16

substantial decrease

based on PAO2 = PIO2 - (PACO2/R)

Question 17

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

Answer 17

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

Question 18

equation for PAO2

Answer 18

PAO2 = PIO2 - (PACO2/R)

Question 19

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

Answer 19

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

Question 20

difference between PACO2 and PaCO2

Answer 20

PACO2 = alveolar

PaCO2 = artery

Question 21

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

PAO2

Answer 21

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

PAO2 = 100 Torr

Question 22

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

Answer 22

if breathe 100% O2, no N2

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

Question 23

2 steps in CO2 removal

Answer 23

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.

Question 24

what is rate limiting step between two steps of CO2 removal

why?

Answer 24

transport of CO2 to outside air (ventilation)

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

Question 25

what does rate limiting step of CO2 removal depend on? what does it affect?

Answer 25

step = transport of CO2 to outside air depends on: 1) alveolar ventilation affects 1) PACO2 2) PaC=O2

Question 26

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

Answer 26

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)

Question 27

PaCO2 and PACO2 assumed to be ____ why?

Answer 27

equal because rapid diffusion of CO2 from blood to alveoli

Question 28

what do PaCO2 and PACO2 depend on?

Answer 28

amount of CO2 being produced relative to alveolar ventilation rate

Question 29

alveolar ventilation equation ***MEMORIZE

Answer 29

``` PACO2 = PaCO2 = (VCO2dot/VAdot) x k k = constant ``` VCO2 dot = Co2 production per minute VAdot = alveolar ventilation per minute

Question 30

what is ideal PaCO2

Answer 30

40 Torr

Question 31

why do we care about having particular PaCO2 = 40 Torr

Answer 31

affects pH

Question 32

define hypoventilation

Answer 32

Low VAdot and High PaCO2 Constant VCO2dot --> incr PaCO2

Question 33

normal value of PaCO2 in Denver with hypoventilation

Answer 33

> 40 Torr

Question 34

Causes of hypoventilation

Answer 34

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

Question 35

define hyperventilation

Answer 35

High VAdot and Low PaCO2 Constant VCO2 dot --> decr PaCO2

Question 36

Causes of hyperventilation

Answer 36

1) high altitude - ventilating more to compensate for low enviorn O2, decr CO2 2) acute hypoxemia 3) metabolic acidosis 4) CNS stimulation

Question 37

define hyperpnia

Answer 37

High VAdot and normal PaCO2 --> PaCO2 unchanged

Question 38

Causes of hyperpnia

Answer 38

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

Question 39

what is partial pressure of water vapor what is PB typically

Answer 39

47 torr 720 at sea level 620 at Denver

Question 40

does partial pressure of water vapor vary with altitudes

Answer 40

no constant

Question 41

does PB vapor vary with altitudes

Answer 41

YES | decr at higher altitudes

Question 42

difference between PAO2 and PaO2

Answer 42

A= alveoli a = arterial

Question 43

why does respiratory exchange occur

Answer 43

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

Question 44

define respiratory exchange ratio in words

Answer 44

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

Question 45

equation for respiratory exchange ratio

Answer 45

R = V(CO2) / V(O2)

Question 46

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

Answer 46

exchange of CO2 for O2 NOT ALWAYS 1:1 because metabolic reactions consume more O2 compared to CO2 avg diet: R = 0.8

Question 47

what are typical R values for carbs fats avg diet

Answer 47

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

Question 48

what is factored into the calculation of alveolar PAO2

Answer 48

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

Question 49

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

Answer 49

PAO2 = PIO2 - (PACO2/R) therefore, PAO2 less than PACO2 because more CO2 in alveolus

Question 50

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

Answer 50

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

Question 51

difference between PACO2 and PaCO2

Answer 51

PACO2 = alveolar PaCO2 = artery

Question 52

PaCO2 and PACO2 assumed to be ____ why?

Answer 52

equal because rapid diffusion of CO2 from blood to alveoli

Question 53

what do PaCO2 and PACO2 depend on?

Answer 53

amount of CO2 being produced relative to alveolar ventilation rate

Question 54

Path for O2 transport

Answer 54

1) O2 entry into lungs 2) entry into pulm capillaries 3) pulm capillaries diffuse into arterial blood

Question 55

Is PaCO2 inversely related to alveolar ventilation?

Answer 55

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

Question 56

What is PaCO2 if VAdot decr by 50%

Answer 56

PaCO2 = (VCO2dot) / (VAdot) x k PaCO2 will double

Question 57

General solution for change in VAdot

Answer 57

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

Question 58

why can we substituTe PACO2 for PaCO2

Answer 58

amount of CO2 essentially same because diffusion is RAPID DECR IN PAO2 WITH CHANGE IN VENTILATION

Question 59

Blood CO2 is ___ regulated by alveolar ventilation

Answer 59

directly

Question 60

___ is directly regulated by alveolar ventilation

Answer 60

Blood CO2

Question 61

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

Answer 61

indirectly

Question 62

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

Answer 62

Blood O2