3. Pulmonary Blood Flow & V/Q

Question 1

where do alveolar caps recieve blood & what are its contents

Answer 1

from RV

low O2 & high CO2

Question 2

what are extra-alveolar caps

Answer 2

recieve blood from LV

high O2 & low CO2

-deliver O2 and CO2 to tissues of lung

Question 3

what is venous admixture

Answer 3

the blood that goes thru extra-alv caps exit into pul V

-reduce PaO2 of arterial blood and increase PaCO2 (slightly)

mixes with blood from alveolar caps (came from alveoli)

Question 4

what is PBP

Answer 4

pul BP = CO * PVR

(PVR = resistance of blood thru lungs)

= 25/15 mm Hg

Question 5

how does the R in pul vasculature and systemic vasculature differ

& what is PVR determined by

Answer 5

PVR = much lower R compared to systemic side

PVR determine by high number caps, how many caps are open at given time (not all open at rest!) & lung vol

Question 6

what happens to PVR with exercise

Answer 6

drops as more pul caps open up to accomodate the increased CO

Question 7

how does lung vol affect PVR

Answer 7

at low (compress vessls) and high (stretch) lung vols –> resistance increases

Question 8

why do you pass out if you lock knees while standing for a long time

Answer 8

gravity pulls blood into legs - less blood returns to heart bc locked knees

w/o locked knees you can use Sk M to increase flow from legs back to thorax

Question 9

what is the BP, blood flow and size of alveoli at the apex of the lung

Answer 9

reduced bc gravity pulls blood down to base

Palv > Pa > Pv

less blood flow & alveoli kinda expanded

Question 10

what is the BP, blood flow and size of alveoli in the middle of the lung

Answer 10

BP little higher than at apex –> Pa > Palv > Pv

normal blood flow

average sized alveoli

Question 11

what is the BP, blood flow and size of alveoli at the base of the lung

Answer 11

higher BP (bc gravity pull blood down to base) –> Pa > Pv > Palv

smaller alveoli

greater blood flow

Question 12

how is blood flow determined

Answer 12

how gravity acts on blood

how much air is in that region

Question 13

what modulates blood flow & what is the result

Answer 13

nitric oxide (made by endothelium)

-cause Sm M relaxation and vasodilation

–> slow down and get more blood

Question 14

what chemical modulators are often present with pathologic conditions

Answer 14

endothelin 1

thromboxane A2

Question 15

why do you have to keep alveoli “dry”

Answer 15

if alveoli have water –> impair the ability of O2 to cross bc its not very h2o soluble

Question 16

what forces favor filtration of fluid from cap to alveoli

Answer 16

Pc

π_tissue

** P_T (diff from rest of body bc its neg)

Question 17

What are the forces that favor movement of fluid out of the alveolus to the capillary?

Answer 17

interstitial oncotic pressure

Question 18

what forces move h2o from alv to cap

Answer 18

π_c

related to proteins in plasma

Question 19

what is the greatest force driving fluid flow back and forth caps/alveoli

Answer 19

Pc

* always favor filtration - Pc + π_t + P_T = larger component in starling equation!

Question 20

Why doesn’t fluid build up in the alveolus if there is a net pressure moving fluid from the capillary to the alveolus?

Answer 20

The lymphatics

–> rapidly remove the fluid

Question 21

What extra-pulmonary disease would contribute to pulmonary edema?

Answer 21

CHF

Question 22

how do lungs play into metabolic fxn

Answer 22

contain ACE –> convert angiotensin 1 to angiotensin 2 & inactivate bradykinin

metabolism of arachidonic acid - breakdown leukotrienes, prostaglandins E2 & F_2alpha

Question 23

what is the equation to solve P_alvO2

Answer 23

Question 24

How do you calculate PI_O2

Answer 24

(barometric P - water vapor P) * fraction of inspired aire

(760-47) * FiO2

(FiO2 normally = 21%)

Question 25

How do you solve for the respiratory quotient (R)?

Answer 25

R = consumption of CO2/Consumption of oxygen. Normally = 200/250 = 0.8 change under certain circumstances (administration of glucose or exercise)

Question 26

what is the A-a O2 gradient what is normal range

Answer 26

P_AO2 - P_aO2 normally \< 20 mm Hg

Question 27

How do you solve for P_AO2 (partial alveolar pressure of O2)?

Answer 27

P_AO2 = PIO2 - (PaCO2/R)

Question 28

What would an increase in the AA gradient indicate?

Answer 28

diffusion impairment. Something is wrong at the alveoli

Question 29

what does it mean if A-a gradient is normal BUT P_aO2 and P_AO2 are low

Answer 29

problem is other than the alveoli -pt maybe hypoventilating

Question 30

Due to gravity pulling intrapleural fluid lower in the intrapleural space, what is the effect on intrapleural pressure?

Answer 30

Intrapleural pressure at the apex = -10 cm H2O (less than normal) & at the base = -2 cm H2O (more than normal) normal = -5

Question 31

why are the alveoli at the apex of the lung large at rest

Answer 31

P_IP is more neg

Question 32

why are the alveoli at the base small at rest

Answer 32

not as expanded bc less neg PIP

Question 33

how are the alveoli in the apex and base affected during inspiration

Answer 33

apex - only get a little larger bc almost fully inflated base - get much larger and have more complliance bc already slightly inflated

Question 34

What is the average V/Q ratio?

Answer 34

0.8 usually described as either high or low

Question 35

What will occur in extreme cases of a low V/Q ratio?

Answer 35

Alveolar and capillary O2 and CO2 pressures equilibrate and there will be a V/Q of 0 - cause by an obstruction

Question 36

What is a V/Q ratio of 0 (aka very low)?

Answer 36

right to left shunt

Question 37

In a low V/Q ratio, what will be the values of PaO2, PaCO2, pHa, and volume of blood?

Answer 37

PaO2: Low PaCO2: High pHa: Low volumbe - high\* relative to ventilation

Question 38

If you have a very high V/Q ratio, what is happening?

Answer 38

no blood is coming to the alveolus --\> becomes alveolar dead space

Question 39

What happens to P_AO2 and P_ACO2 in a high V/Q ratio?

Answer 39

equilibrate with the atmosphere so in alveoli O2 gets very high & CO2 gets very low (not much blood benefits from this bc little blood flowing thru)

Question 40

If you have a high V/Q due to lack of blood flow, what happens in other alveoli?

Answer 40

other alveoli --\> low V/Q ratio bc increased blood flow to the area

Question 41

In a high V/Q ratio, what are the values of PaO2, PaCO2, pHa, and volume of blood?

Answer 41

PaO2- High PaCO2- Low pHa- High Volume of blood: Low

Question 42

What is the V/Q ratio at the apex of the lung?

Answer 42

high | (high PaO2 and low PaCO2)

Question 43

What is the the V/Q ratio at the vase base of the lung?

Answer 43

low | (low PaO2 and high PaCO2)

Question 44

What is the V/Q ratio in the middle of the lung?

Answer 44

normal, about 0.8