assessment of V/Q

Question 1

what is V/Q ratio?

Answer 1

quantitative measurement of gas exchange

–> bsed on imbalances of ventilation/perfusion

Question 2

what does normal V/Q mean?

Answer 2

V/Q = 1

normal perfusion/ventilation

blood gases equilibrate with alveolar gas

Question 3

if V/Q = infinity (HIGH)

Answer 3

normal ventilation but no perfusion

alveolar gas equlirates with inspired, humidified air

NO OXYGENATION OF BLOOD

Question 4

IF V/Q = 0

Answer 4

normal perfusion but no ventilation

alveolar gases equilibrate with blood gases

NO OXYGENATION OF BLOOD

Question 5

Regional abnormalities in lung

upper lobe

lower lobe

overall lung

Answer 5

1) upper lobe = ventilated but relatively under perfused V/Q = 2.5
2) Lower lobes = perfused but relatively under ventilated

V/Q = 0.6

3) overall lung- normal = slightly less than ideal

V/Q ~0.8

Question 6

Local regulation of V/Q

High V/Q

Answer 6

– Alveolar Pco2 drops (as equlibrate with air not blood) = bronchoconstrictor

– Increases local airway resistance

– Decreases ventilation

– Lowers V/Q

Question 7

LOCAL regulation of V/Q

Low V/Q

Answer 7

– Alveolar Po2 drops

– Hypoxic pulmonary vasoconstriction
– Decreases perfusion
– Increases V/Q

Question 8

normal numbers for ***memorize

PaO2

PaCO2

SAT

CaO2

CaCO2

at sea level and Denver

Answer 8

Question 9

where is anatomic dead space

Answer 9

all airway no gas exchange

(trachea, bronchi, bronchioles, and first 16 branch oints of respiratory tree)

–> 1/3 VT

Question 10

what is alveolar dead space

Answer 10

ventilation of unperfused alveoli

Question 11

where is physiologic dead space

Answer 11

Vphys = Vanat + Valv

Question 12

if V/Q > 1 and dead space

Answer 12

wasted alveolar ventilation and ventilation of anatomic dead space

Question 13

Problems with dead space

Answer 13

high V/Q

• work without benefit of oxygenating blood
• generally doesn’t cause hypoxemia (decr PaO2 unless severe)
• can cause incr PaCO2

Question 14

dead space generally doesn’t
cause

Answer 14

hypoxemia (decr PaO2 unless severe)

Question 15

why do you decr dead space with exercise

Answer 15

incr ventilation and O2 delivery to your lungs

Question 19

how can incr dead space inr PaCO2

what is PaCO2 regulated by?

Answer 19

1) CO2 production
2) minute ventilation (freq x VT)
3) dead space

Question 20

what is equation for VAdot

Answer 20

VAdot = freq x (VT - VD)

Question 21

what is hyperventilation

Answer 21

ventilation in
XS of metabolic needs = blowing off more CO2 than producing

VE = 1000 mL x 10/min = 10 L

VA = 8.5 L

Question 22

what is hypoventilation

Answer 22

VE = 250 mL x 40/,min = 10L

VA = 4L

hypoventilation = unable to blow off all CO2
insufficient metabolic needs —> incr PaCO2, decr VAdot

Question 24

Dead space is about ___ of tidal volume

Answer 24

~ 1/3 of tidal volume

breathing really fast, hypoventilation

Question 25

Causes of dead space

Answer 25

1) Rapid shallow breathing
2) Pulmonary Embolus
3) Decreased Cardiac Output
4) Mechanical ventilation
5) Emphysema

Question 26

what is a true shunt

Answer 26

V/Q <1

blood passing through capillaries that does not get oxygenated

Question 27

what is a known physiologic shunt

Answer 27

bronchial circulation

1-2% CO

Question 29

Shunt and Low V/Q units contribute to:

Answer 29

1) arterial hypoxemia (decr PaO2)
2) arterial hypercapnea (incr PaCO2)

Question 30

Shunt is the ___ of Low V/Q

Answer 30

extreme