Resp. Physiology SDL Flashcards
When air is inspired (before it reaches the lungs) what occurs
It is warmed to body temperature and saturated with water vapour.
what is the volume of gas inspired at each breath
tidal volume VE
what is the the fraction of air inspired at each breath called
alveolar ventilation VA
what does the remainder of inspired volume occupy
dead space VD
which consists mainly of conduction airways
what occurs to the dead space gas in expiration
it is expelled first and is followed by alveolar gas which partially mixes with it
what does the dead space contain at the end of expiration
only alveolar gas
what is the volume of gas expired at each breath
expired volume (VE)
what is the gas expired at each breath made up of
- alveolar ventilation VA
- dead space ventilation VD
what is the volume of CO2 produced per breath
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
what is needed to measure volume and composition of bulk expired gas at rest
- Respiratory valve unit (with mouth piece and nose clip)
- Three way stopcock* (and connecting tube to respiratory valve unit)
- Douglas bag (100 litres) for collection of expired gas
- Wet gas meter for measurement of expired gas volume
how is volume & composition of bulk expired gas at rest measured
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.
how is gas measured expressed as a partial pressure
Px = Fx (PB - PH2O)
Px, PB, PH2O expressed as mmHG
Fx = expressed as decimal fraction
how is the rate of CO2 production measured
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
how is O2 rate of consumption measured
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
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
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
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
decreased VA
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
you will have substantially raised CpvO2
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
atmospheric air is 21% O2
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
it should be collected at the end of exhalation
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
lower alveolar water vapour pressure
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
VdotA is 5.0 l min-1
