Alveolar Ventilation/Perfusion

Question 1

what is the alveolar gas equation?

Answer 1

subtract 47 from barometric pressure…multiply this by the functional percent of the gas, then subtract the supposed amount of CO2 and you will get the amount O2 expected in the alveolar gas

Question 2

what is the equation to determine what the expected arterial blood gas and alveolar blood gas of O2 difference should be?

Answer 2

age divided by 4 then add 4

Question 3

what is the alveolar ventilation equation?

Answer 3

Va=0.863(VCO2)/PACO2

Question 4

how is alveolar ventilation related to arteriole pressure of CO2?

Answer 4

inversely…if PACO2 doubles then alveolar ventilation is halved

Question 5

what is the main driver of ventilation?

Answer 5

PaCO2

Question 6

what portion of the lung has the highest pressure?

Answer 6

the top

Question 7

which area of the lung, top middle or bottom, opens to a greater extent during ventilation? why?

Answer 7

the bottom does…this is because the alveoli are less opened already and so small amounts of pressure open them more compared to the top

Question 8

are capillaries in the pulmonary system susceptible to alveolar air pressure?

Answer 8

yes

Question 9

which type of pulmonary vessel decreases resistance when alveolar pressure increases?

Answer 9

extra-alveolar vessels

Question 10

which type of pulmonary vessel increases resistance when alveolar pressure increases?

Answer 10

the alveolar vessels

Question 11

are the pulmonary alveolar vessels sensitive to arterial or venous pressure or both? what is the response to increasing pressure in either system?

Answer 11

they are sensitive to both…as both increase pressure the vessel dilates in response and the resistance of the vessel drops

Question 12

which portion of the lung receives the most blood volume?

Answer 12

the bottom by far

Question 13

in terms of the three pressures, alveolar arterial and venous, order them in increasing order for the top of the lung and explain the cause this has on the vessel and perfusion?

Answer 13

venous to arterial to alveolar (highest)

this means the vessel will be constricted and perfusion limited

Question 14

in terms of the three pressures, alveolar arterial and venous, order them in increasing order for the middle of the lung and explain the cause this has on the vessel and perfusion?

Answer 14

venous to alveolar to arteriole (highest)

this means at the arterial end of the vessel it will be dilated and have some perfusion but at the end of the vessel there is limited flow due to alveolar pressure being higher than venous

Question 15

in terms of the three pressures, alveolar arterial and venous, order them in increasing order for the base of the lung and explain the cause this has on the vessel and perfusion?

Answer 15

alveolar to venous to arterial (highest)

this means the vessel is dilated throughout the alevolar area

Question 16

what area of the lung has the highest V/Q ratio? why is this?

Answer 16

the top…the ventilation is really low up here and so is the perfusion but the perfusion is kept super low to prevent any mismatch

Question 17

what area of the lung has the highest PAO2?

Answer 17

top of the lung due to the high V:Q mismatch

Question 18

the base of the lung has a high or low V:Q? why?

Answer 18

a lower V:Q because it gets lots of blood flow and also gets lots of ventilation

Question 19

what is hypoxic pulmonary vasoconstriction?

Answer 19

if there is low alveolar PO2 then the pulmonary arteries feeding that area will constrict

Question 20

what does hypoxic pulmonary vasoconstriction do to V:Q?

Answer 20

preserves it and keeps it from mismatching

Question 21

what causes the alveoli to be held more open in the apex of the lung?

Answer 21

the higher intrapleural pressure that is there and the force of gravity

Question 22

are top of the lung alveoli high or low compliance?

Answer 22

low compliance

Question 23

what are the changes seen in extra alveolar vessels when air volume increases? what about when lung volume decreases?

Answer 23

they have less resistance and expand

they have more resistance and contract

Question 24

do alveolar vessels increase or decrease resistance when lung volume increases?

Answer 24

they increase their resistance