Resp. Physiology SDL

Question 1

When air is inspired (before it reaches the lungs) what occurs

Answer 1

It is warmed to body temperature and saturated with water vapour.

Question 2

what is the volume of gas inspired at each breath

Answer 2

tidal volume V_E

Question 3

what is the the fraction of air inspired at each breath called

Answer 3

alveolar ventilation V_A

Question 4

what does the remainder of inspired volume occupy

Answer 4

dead space V_D

which consists mainly of conduction airways

Question 5

what occurs to the dead space gas in expiration

Answer 5

it is expelled first and is followed by alveolar gas which partially mixes with it

Question 6

what does the dead space contain at the end of expiration

Answer 6

only alveolar gas

Question 7

what is the volume of gas expired at each breath

Answer 7

expired volume (V_E)

Question 8

what is the gas expired at each breath made up of

Answer 8

1. alveolar ventilation V_A
2. dead space ventilation V_D

Question 9

what is the volume of CO2 produced per breath

Answer 9

VCO2 = VE x FECO2

product of expired gas volume and the fractional concentration of CO2.

But since inspired gas normally contains virtually no CO2, all the CO2 in mixed expired gas must come from the alveoli.

VCO2 = VA x FACO2

So the volume of CO2 produced per breath is:
(Vᴇ x FᴇCO₂) x (Vᴀ x FᴀCO₂)

But we want to know VA, so we have to rearrange the equation to:

VA = VE x FECO2/FACO2

Question 10

what is needed to measure volume and composition of bulk expired gas at rest

Answer 10

1. Respiratory valve unit (with mouth piece and nose clip)
2. Three way stopcock* (and connecting tube to respiratory valve unit)
3. Douglas bag (100 litres) for collection of expired gas
4. Wet gas meter for measurement of expired gas volume

Question 11

how is volume & composition of bulk expired gas at rest measured

Answer 11

When breathing is steady, rotate the stopclock to start collecting expired gas into the Douglas bag. Simultaneously, start the timer and begin counting breaths. After 1 to 2 minutes, rotate the stopclock back to its original position to trap air in the Douglas bag, whose volume can be measured in a gas meter. You can now calculate the volume expired per breath.

Question 12

how is gas measured expressed as a partial pressure

Answer 12

Px = Fx (P_B - P_H2O)

Px, P_B, P_H2O expressed as mmHG

Fx = expressed as decimal fraction

Question 13

how is the rate of CO2 production measured

Answer 13

expressed as volume

V̇CO2 = V̇E x FECO2 – V̇I x FICO23

But when breathing atmospheric air, FICO2 is negligible (0.03 %), so:

V̇CO2 = V̇E x FECO2

Question 14

how is O2 rate of consumption measured

Answer 14

V̇O2 = V̇I x FIO2 - V̇E x FEO2

But in this case, FIO2 is not negligible (normally 20.9%).

Additionally, V̇I and V̇E may not be the same because V̇O2 and V̇CO2 may differ.

So you have to look at the Nitrogen Concentration too because you have to calculate for the fact that inspired and expired air may differ.

V̇E is known (measured)

V̇I is calculated from nitrogen concentrations in inspired and expired gas

Question 15

Alveolar air and systemic arterial blood O2 tension in a student were respectively: PAO2 = 100mmHg, PaO2 = 70mmHg. Which ONE of the following is the best explanation:-

a. The student may just have been breath-holding
b. The figures could be explained by a pathological right to left shunt
c. These values can be explained by low pulmonary Q
d. These values would be reasonable for someone living at high altitude
e. These are typical values for a healthy person

Answer 15

a. The student may just have been breath-holding

b. The figures could be explained by a pathological right to left shunt

c. These values can be explained by low pulmonary Q
d. These values would be reasonable for someone living at high altitude
e. These are typical values for a healthy person

Question 16

2) In a situation where you are rebreathing room air (from a bag) which ONE of the following scenarios is false?

Select one:

a. very likely f will have increased
b. you have increased VE
c. you have raised inspired PCO2
d. you will have decreased VA

Answer 16

decreased VA

Question 17

After Hyperventilation with pure O2 which ONE of the following scenarios is false?

Select one:

a. you will have substantially raised CpvO2
b. you will see raised P AO2
c. you will see lower PACO2
d. you will have markedly raised PpvO2
e. you will have increased breath-holding time but not by an effect on blood O2 loading

Answer 17

you will have substantially raised CpvO2

Question 18

4) About respiration in a climber on top of Mt Everest, assuming Patm there = 247mmHg. Only ONE of the following statements is correct

Select one:

a. tracheal air PO2 will be about 149mmHg-
b. Low pressure gradient from atm to lung makes breathing difficult
c. survival is threatened by resulting anaemic hypoxia
d. atmospheric air is 21% O2
e. inspired (atmospheric) air PO2 will be 160 mmHg

Answer 18

atmospheric air is 21% O2

Question 19

5) To measure alveolar gas composition, which one is CORRECT?

Select one:

a. its O2 tension will be similar to dead space
b. it should be collected at the end of exhalation
c. it will contain air with more water vapour than dead space
d. its CO2 tension will be similar to dead space
e. It should be collected at the start of exhalation

Answer 19

it should be collected at the end of exhalation

Question 20

6) Which one of the following is FALSE? Breath-holding will

Select one:

a. break when PaCO2 exceeds 40mmHg
b. lower alveolar water vapour pressure
c. Lower VdotE
d. raise PACO2
e. lower PAO2

Answer 20

lower alveolar water vapour pressure

Question 21

7) Minute expired volume in a male student was measured as 6.5 l/min. fR = 20 min-1.Which ONE of the following is FALSE Assuming that VA is 2/3 of VE ?-

Select one:

a. Only 215ml fresh inspired air is available per breath for respiratory gas exchange
b. VE is 325ml/breath
c. VD is 110ml/breath
d. VdotA is 5.0 l min-1
e. VdotE = 6.5 l min-1

Answer 21

VdotA is 5.0 l min-1