Respiratory Physiology II

Question 1

*Identify the average V/Q ratio in a normal lung and describe its significance in determining gas exchange

Answer 1

A

Question 2

*Characterize the normal regional differences from the apex to base of the lung in blood flow ,ventilation, V/Q, PO2, PCO2, and pH

Answer 2

A

Question 3

*Be able to calculate the alveolar to arterial PO2 difference (A-a) O2. Describe the normal value for (A-a) O2 and significance and Elevated (A-a) O2.

Answer 3

A

Question 4

*Name five causes of Hypoxemia. Describe the effect of each cause on (A-a) O2 and whether supplementary O2 will correct hypoxemia.

Answer 4

A

Question 5

*Compare shunts and dead space. Describe the consequences of each on alveolar PO2 and PCO2.

Answer 5

A

Question 6

*.Describe the physiologic response to low and high V/Q to compensate

Answer 6

A

Question 7

• What is the crucial factor in determining the alveolar pressure, and therefore arterial PO2, and PCO2?

Answer 7

The V/Q ratio (ventilation/perfusion) is crucial factor in determining alveolar pressure, arterial Po2, Pco2.

Question 8

Describe the ventilation and perfusion at the apex of the upright lung, as well as V/Q, PCO2 and PO2.

Answer 8

At the APEX of the upright lung: Alveoli are POORLY Ventilated and perfused, but they are BETTER VENTILATED than perfused leading to HIGH V/Q with a high PO2 and Low PCO2.

Question 9

What occurs when there is a poor perfusion but good ventilation?

Answer 9

When there is poor perfusion, but good ventilation, the ALVEOLAR gas pressure is SIMILAR to INSPIRED air (PAO2= 150, PA CO2= 0)

Question 10

Describe the level of ventilation and perfusion at the base of upright lung as well as V/Q, PCO2 and PO2

Answer 10

At the BASE of upright lung: Alveoli are WELL Ventilated and Perfused, but they are BETTER PERFUSED than ventilated, hence leading to LOW V/Q with Low Po2 and HIGH PCO2.

Question 11

What occurs when there is poor ventilation but good perfusion?

Answer 11

When there is Poor Ventilation but good perfusion, Alveolar gas pressure is SIMILAR to MIXED VENOUS Blood (PAO2= 40, PACO2= 45)

Question 12

What is the use of A-a O2 gradient and what can this indicate?

Answer 12

The A-a O2 gradient can be determined using the alveolar gas equation and arterial blood gases; This gradient measures the EFFICENCY of GAS EXCHANGE across alveolar-capillary membrane and can point to CAUSE of HYPOXEMIA

Question 13

What is a normal A-a O2 gradient value? why is this the case?

Answer 13

A Normal A-a O2 gradient is < or equal to 20 mmHg, duet to normal V/Q mismatch and shunting of bronchial and coronary blood into Thesbian veins back to left side of heart.

Question 14

How can the Normal A-a O2 gradient be predicted? What equation is used? What happens to this gradient as we age?

Answer 14

Normal A-A O2 gradient can be predicted by equation: Age/4 +4. The A-a O2 gradient INCREASES as we Age (get older)

Question 15

What are the five main causes of Hypoxemia? describe how each cause affects A-a O2 gradient.

Answer 15

5 main causes of hypoxemia:

1. Hypoventilation - A-a2 O2 gradient is NORMAL
2. Low inspired Oxygen (at high altitude; low barometer Pressure; A-a O2 gradient is NORMAL
3. Right to Left Shunt- A-a gradient is INCREASED
4. Ventilation/Perfusion (V/Q) Mismatch; A-a O2 gradient is INCREASED
5. Diffusion Limitation (reduced gas exchange) ; A-a O2 gradient is INCREASED

Question 16

Which of causes of hypoxemia have a normal vs increased A-a gradient? Which of the causes can have a response to O2 therapy?

Answer 16

-Low inspiration and Hypoventilation both have Normal A-a O2 gradient
- Right to Left shunt, V/Q Mismatch and Diffusion Limitation ALL have Widened or increased A-a O2 gradients.
Low inspiration, hypoventilation, diffusion and V/Q mismatch will respond to O2 therapy.

Question 17

Which of the following causes of hypoxemia is the ONLY one that will NOT have a response to Oxygen therapy.

Answer 17

RIGHT to LEFT SHUNT= NO response to O2 therapy.
R to L shunt is only cause of hypoxemia in which arterial Po2 fails to raise to expected level if 100% of O2 administered.
R to L shunt (area where no gas exchange occurs)

Question 18

*Define the partial pressure and fractional concentration as they apply to gases in the air. List the normal fractional concentrations and sea level partial pressures for O2, CO2, and N2

Answer 18

A

Question 19

*Define and contrast the following terms: Anatomic dead space, alveolar dead space, physiological dead space, total minute ventilation and alveolar minute ventilation

Answer 19

A

Question 20

*Describe the effect of different breathing patterns on total minute and alveolar ventilation

Answer 20

A

Question 21

*Describe the alveolar gas equation and its use

Answer 21

A

Question 22

*Define the following terms: Hypoventilation, Hyperventilation, Hypercapnea, eucapnia, hypocapnea

Answer 22

A

Question 23

*Use the PCo2 equation to describe the relationship between ventilation and CO2.

Answer 23

A

Question 24

Define both total pressure and partial pressure

Answer 24

Total pressure: the SUM of the partial pressures of gas must equal to total pressure
Partial pressure of gas = fraction of gas (% of gas) in the gas mixture x Total pressure
ex: find PN2, use 760 mmHg x % of gas in mixture (ex;21%)
PN2= 760 mm Hg x 0.21 = 160 mm Hg

Question 25

What happens to inspired gas that has reached the trachea? Describe the changes associated.

Answer 25

By the time INSPIRED gas has reached the Trachea, it is FULLY SATURATED with water vapor, which exerts a pressure of 47mm Hg at body temp and dilutes the partial pressures of N2 and O2.

Question 26

Why do the partial pressures of O2, N2, and H2O vapor remain unchanged until it reaches alveolus?

Answer 26

The conducting airways DO NOT participate in Gas exchange, and therefore partial pressures of N2, O2, and H2O water vapor remain unchanged in airways until gas reaches the alveolus.

Question 27

*Describe what minute ventilation is and the equation that is used. Which component of equation is more important when minute ventilation increases?

Answer 27

Minute Ventilation- the amount of total gas ventilated in one minute
minute ventilation (VE) = Tidal volume (VT) x Breathing frequency (f) 
VE= VT (ml/breath)  x f, respiratory rate (breaths/min)
VT (Tidal Volume) is more important than respiratory rate when minute ventilation increases.

Question 28

What is anatomical dead space value? how is it represented?

Answer 28

Anatomical dead space (150 ml) - volume of air filled in conducting airways that are uncapable of gas exchange in blood. Hence dead space - 150 ml.

Question 29

Describe the minute ventilation at rest. How might this change after exercise?

Answer 29

At rest: VE (minute ventilation)= Vt x F
6000 mL= 500 x 12
With exercise VE can increase by 25 fold to 150 L/min)

Question 30

*What is alveolar ventilation? What are the components and equation? What must you consider?

Answer 30

Alveolar ventilation- amount of air reaching the alveoli per minute
Alveolar ventilation= (tidal volume -dead space) x respiratory rate (breathing frequency
VA= (VT - VD) x f, respiratory rate
To determine alveolar ventilation, you must take into account dead space.

Question 31

*Describe the changes in alveolar ventilation that occur at rest, breathing slowly and breathing rapidly.

Answer 31

At rest: VA = (VT - VD) x f
VA=4,200 ml= (500 - 150 (dead space) x 12
Breathing DEEPLY and SLOWLY: VE stays the SAME and VA INCREASES

Breathing Shallowly/RAPIDLY: VE stays the SAME, and VA DECREASES (even to zero)

Question 32

*Describe the relationship between VA and PaCO2. What happens when you hyperventilate vs hypoventilate?

Answer 32

VA and PaCO2 are INVERSELY related.
When VA increases, PaCO2 decreases.
Hence when you hyperventilate, increase VA , so PaCO2 decreases.
When you hypoventilate, you Decrease VA, so PaCO2 increases.

Question 33

*What is the difference between anatomocial dead space, physiological dead space and alveolar dead space?

Answer 33

Anatomical dead space- air filled in CONDUCTING airways (nose to term bronchioles) and does not participate in gas exchange
Physiological dead space- SUM of all parts of TIDAL volume that does not participate in gas exchange. Physio dead space = Anatomical dead space + alveolar dead space

alveolar dead space- volume of air that fill alveoli (gas exchange regions) But DOES not undergo gas exchange

Question 34

*What is an alternate way to calculate alveolar ventilation if there is NO dead space? What is the PCO2 equation?

Answer 34

Alternate way To calculate alveolar ventilation:
VA= VECO2 x 0.863/PACO2
VECO2= volume of CO2 exhaled per min
0.863= constant
in clinical setting you can substitute, arterial PaCO2 for PACO2.
PCO2= VCO2 x 0.863/VA

Question 35

*What is hypercapnia, Eucapnia and hypocapnia?

Answer 35

Hypercapnia- INCREASED CO2 levels in blood
Hypocapnia- REDUCED CO2 levels in blood
Eucapnia- NORMAL, healthy CO2 levels in blood

Question 36

What is the use of alveolar gas equation? What is the PAO2 at seat level.

Answer 36

Partial pressure of Oxygen in the Alveolus is given by Alveolar gas equation
PAO2= FIO2 (PB-PH20) - (PACO2/R)
PIO2= substitute FIO2 (PB- PH20)
R= respiratory quotient (ratio of CO2 produced to O2 consumed; VCO2/VO2) in a mixed diet: R= 0.8
PAO2= FIO2 (PB-PH20) - (PACO2/R)
At sea level, R=0.8, PAO2= 0.21(760- 47) - (40/0.8)
PAO2= 100.
PIO2= partial pressure of inspired oxygen.

Question 37

*Define partial pressure and fraction concentration. List the normal fractional concentrations and sea level particle pressures for O2, CO2, and N2

Answer 37

Total pressure: the SUM of the partial pressures of gas
Partial pressure of gas = fraction of gas (% of gas) in the gas mixture x Total pressure
1. PN2= 760 mm Hg x % of gas in mixture (79%=0.79)
PN2= 760 x 0.79=600 mmHg
2. PO2 = 760 mm Hg x % of gas in mixture (21%= 0.21)
PO2= 760 x 0.21= 160 mmHg
3. PCO2= 760 mm Hg x % of gas in mixture (0.03%=0.003)
PCO2= 760 x 0.003= 0.24 mm Hg (which is negligible)