Alveolar Ventilation

Question 1

ventilation

Answer 1

the movement of fresh gas into the lungs for gas exchange, and movement of that gas back out of the lungs

Question 2

what is inspired air and what happens to it as it gets breathed in

Answer 2

environmental air; gets heated to body temperature and fully humidified when inhaled

Question 3

what is FIO2

Answer 3

fraction of O2 in inspired gas

at sea level FIO2 = 21%

Question 4

what is the partial pressure of water vapor

Answer 4

50 mmHg

causes a drop in PO2 in the air as it travels into alveoli

Question 5

equation for inspired air PO2 (PIO2)

Answer 5

PIO2 = FIO2 (PB - PH2O)

PIO2 = 149 mmHg at sea level

Question 6

what is barometric pressure

Answer 6

760 mmHg

Question 7

tidal volume

Answer 7

the volume of air moved with each breath

measured on expiration since volume in does not equal volume out

Question 8

tidal volume equation

Answer 8

VT = VD + VA

VD = vol of air in dead space
VA = vol of air in alveoli

Question 9

normal tidal volume

Answer 9

10-20 mL/kg

Question 10

minute ventilation

Answer 10

volume of air exhaled in one minute

Question 11

minute ventilation equation

Answer 11

minute ventilation = VT x RR

Question 12

anatomic dead space

Answer 12

amount of tidal volume that doesn’t reach alveoli - remains in conducting airways and does NOT participate in gas exchange

NORMAL - can not change

Question 13

alveolar dead space

Answer 13

amount of tidal volume that reaches alveoli but does not participate in gas exchange due to lack of perfusion to the alveolus

ABNORMAL - all should be perfused in health

Question 14

physiologic dead space

Answer 14

the amount of minute ventilation that goes to dead space (anatomic or alveolar)

considered wasted ventilation

Question 15

is VA equal to the total volume of gas in the alveoli

Answer 15

NO - it is the volume that reaches the alveoli per breath

Question 16

alveolar ventilation

Answer 16

the part of minute ventilation coming from the gas exchange regions

alveolar ventilation = VA x RR

Question 17

how does CO2 diffuse

Answer 17

along partial pressure gradient

tissues –> blood –> lungs –> pulmonary capillaries –> alveolar gas

Question 18

alveolar CO2 (PACO2)

Answer 18

CO2 added to alveolar gas by pulmonary arterial blood and removed by alveolar ventilation

Question 19

how is PACO2 related to alveolar ventilation

Answer 19

INVERSE

high ventilation = low PACO2 because more gas exchange is occurring

Question 20

where does all CO2 come from

Answer 20

tissues (do NOT inspire CO2)

Question 21

arterial PCO2 (PaCO2)

Answer 21

CO2 added to arterial blood from production in tissues

Question 22

how are arterial and alveolar PCO2 related

Answer 22

nearly equal because CO2 is highly diffusible

Question 23

how is PaCO2 related to alveolar ventilation

Answer 23

INVERSE

high ventilation = low PaCO2 because more gas exchange is occurring

Question 24

what is the ONLY way to measure ventilation

Answer 24

PCO2 in arterial or venous blood (ideally arterial)

PaCO2 should be 35-45 mmHg

Question 25

hypoventilation

Answer 25

low alveolar ventilation leading to low CO2 output --> high CO2 remaining in body causes hypercapnia (high PA and PaCO2)

Question 26

how can hypoventilation cause hypoxemia

Answer 26

high PaCO2 leaves less room available for O2, causing PaO2 to decrease

Question 27

is hypoventilation caused by respiratory rate or tidal volume

Answer 27

NO - can have any RR and still be hypoventilating

Question 28

hyperventilation

Answer 28

high alveolar ventilation resulting in high CO2 output --> low CO2 remaining in the body causes hypocapnia (low PA and PaCO2)

Question 29

alveolar gas equation

Answer 29

PAO2 = inspired PO2 - (PACO2 / R) inspired PO2 = 149 mmHg R = 0.8 (respiratory exchange ratio)

Question 30

how can you use alveolar PO2 to evaluate arterial PO2

Answer 30

PAO2 is the maximum value that PaO2 can be PaO2 is usually slightly lower than PAO2 (5-15 mmHg)

Question 31

what does it mean if PAO2 is lower than PaO2

Answer 31

low inspired O2 (altitude) or high arterial O2 (hyperventilation)

Question 32

what does it mean if PaO2 is significantly lower than PAO2

Answer 32

1. decreased O2 delivery 2. increased O2 consumption 3. Hbg deficiency/abnormality