alveolar gas equation/oxygen deprivation/ V/Q

Question 1

alveolar gas equation

Answer 1

PAO2 = PIO2 - PaCO2/R = 150mmHG - PaCO2/0.8

PA02 = alveolar PO2
PIO2 = PO2 in inspired air
PaCO2 = arterial PCO2
R=respitatoy quotient = CO2 produced/O2 CONSUMED

Question 2

what is R in alveolar gas equation

Answer 2

R=respitatoy quotient = CO2 produced/O2 CONSUMED

normally is 0.8

Question 3

PO2 in inspired air in see level (and why)

Answer 3

150mmHg
Ptotal (760) - correction because of trachea (47)
= 713
713 x 0.21 = 150 mmHg

Question 4

A-a gradient:

equation

Answer 4

A-a gradient = alveolar PO2 - arterial PO2

Question 5

A-a gradient - normal values

Answer 5

10-15 mmHg

Question 6

increased A-a gradient may occur in ….

situations:

Answer 6

hypoxemia

causes include: shunting, V/Q mismatch, fibrosis (impairs diffusion)

Question 7

oxygen deprivation in tissues - types

Answer 7

1. hypoxemia
2. hypoxia
3. Ischemia

Question 8

what is hypoxemia

Answer 8

decreased arterial PCO2

Question 9

what is hypoxia

Answer 9

decreased O2 delivery to tissues

Question 10

what is ischemia

Answer 10

loss of blood flow

Question 11

causes of hypoxemia (divide by A-a gradient)

Answer 11

normal A-a gradient: a. high altitude, hypoventilation (eg opioid)
increased A-a gradient: a. V/Q mismatch b. Diffusion limitation (eg. fibrosis) c. Right-to-left shunt

Question 12

causes of hypoxia

Answer 12

1. HYPOXEMIA
2. anemia
3. decreased cardiac output
4. CO poisoning

Question 13

causes of ischemia

Answer 13

1. impeded arterial flow

2. decreased venous drainage

Question 14

V/Q means

Answer 14

ventilation/perfusion

Question 15

V/Q ideally

Answer 15

ideally ventilation is matched to perfusion (V/Q = 1) for adequate gas exchange

Question 16

V/Q lung zones and explanation

Answer 16

V/Q at apex = 3 –> wasted ventilation

V/Q at base = 0.6 –> wasted perfusion

Question 17

V/Q: P artery (Pa) P venous (Pv) P alveoli (PA)

bigger, smaller in the apex of the lung

Answer 17

PA>Pa>PV

Question 18

V/Q: P artery (Pa) P venous (Pv) P alveoli (PA)

bigger, smaller in the middle of the lung

Answer 18

Pa>PA>PV

Question 19

V/Q: P artery (Pa) P venous (Pv) P alveoli (PA)

bigger, smaller in the base of the lung

Answer 19

Pa>PV>PA

Question 20

V/Q=0 - explanation

Answer 20

airway obstruction (SHUNT)
100% O2 does not improve alveolar PO2

Question 21

V/Q=0 –> if 100% O2–> alveolar PO2

Answer 21

does not improve

Question 22

V/Q = infinity

Answer 22

blood flow obstruction (physiologic dead space)

Question 23

assuming 100% O2?

Answer 23

It improves PaO2

Question 24

V/Q – > response to exercise

Answer 24

increased cardiac output –> vasodilation of apical capillaries –> V/Q ratio approaches 1

Question 25

organism that thrive in high O2- area in the lungs

and example

Answer 25

apex

ex. TB

Question 26

V, Q, V/Q ratio distribution in apex, base and middle of the lung

Answer 26

V/Q as apex as higher (0.6 at base, 3 at apex)
Both V and Q are greater at the base, but the increasing of Q from apex to base is greater from the increasing of V and thats why V/Q is decreased in the base (0.6)

Question 27

hypoventilation causes hypoxemia - why

Answer 27

hypoventilation –> increased PaCO2–>increased PACO2 –> decreased PAO2

Question 28

PaCO2 - equation

Answer 28

PaCO2 = K x VCO2 / VA
VA: alveolar ventilation
VCO2: rate of elimination

Question 29

increased VCO2 - situations

Answer 29

fever
exercise
overconsumption of carbohydrates
chill tetanus