pk1 Gas Laws and Ventilation Flashcards
How is metabolic rate measured?
O2 consumption rate or CO2 production rate.
What is the average basal metabolic rate?
250ml/O2/min
What is the daily average metabolic rate?
1000ml/O2/min
What is the average metabolic rate during exercise?
Up to 3000ml/O2/min
Which value relates the rate of consumption of O2 to the rate of production of CO2?
How is this value calculated?
RQ
Vco2/Vo2
What is the RQ of carbohydrate?
1.0
What is the RQ of protein?
0.81
What is the RQ of fat?
0.7
What is the RQ of a well balanced diet?
0.8
What is the name given to generation 0?
Trachea.
What is the name given to generation 10?
Small Bronchi.
What is the name given to generation 14?
Bronchioles.
What is the name given to generation 17?
Respiratory Bronchioles.
What is the name given to generation 23?
Alveolar Sacs.
What is the equation for flow?
V. = uA
V = Flow (cm^3/sec) u = Gas Speed (cm/sec) A = Total Area (cm^2)
At which generation is gas exchange determined by diffusion rather than convection?
Generation 17.
Why does gas exchange depend on diffusion rather than convection at late generations?
V. = uA
A becomes so large that u is down to the speed of molecular diffusion.
Which generations comprise the conducting zone?
Which generations comprise the transitional and respiratory zones?
Conducting zone: 0-16
Transitional and respiratory zone: 17-23
List 3 factors that affect the rate of diffusion of gases.
Partial pressure gradients.
Temperature
Diffusion distance
What is Barometric pressure (Pb)?
The pressure exerted by the weight of gas molecules in the atmosphere above the point of measurement.
What is atmospheric pressure at sea level?
100kPa
How does atmospheric pressure change with altitude?
Atmospheric pressure decreases exponentially with altitude.
It halves every 5450m.
Which two variables affect partial pressure?
1 - The number of molecules of that gas in the given volume.
2 - Temperature.
What is the equation for total pressure?
P1 + P2 + P3 + … Pn
Where p = partial pressure of any individual gas.
Calculate the total atmospheric pressure at sea level. Show the working.
Total pressure = PN2 + PO2 + PH2O + PCO2
Total pressure = 74 + 21 + 5 + 0 = 100kPa.
What is the equation for partial pressure?
Partial pressure = Fractional Concentration * Total Pressure
What is dead space?
The volume of gas within the respiratory system in which gas exchange does not occur.
Occupied by the conducting zone.
Why do we have a conducting zone?
It is a result of internalising the lungs.
Why might alveolar dead space arise?
Because of respiratory diseases.
What is the approximate volume of the anatomical dead space of the respiratory system in an adult male?
150ml
In a healthy person, what is the alveolar dead space?
Normally 0ml.
What is the physiological dead space?
Anatomic Dead Space + Alveolar Dead Space
What is the main factor affecting anatomic dead space?
The size of the subject.
List 2 diseases that can increase alveolar dead space due to under-perfusion of alveoli.
1 - Pulmonary hypotension.
2 - Pulmonary embolism.
Why does increasing physiological dead space impact adversely on blood oxygenation?
Because increasing physiological dead space decreases alveolar ventilation.
This is because air in the dead space does not reach the alveoli.
What is the equation for minute ventilation?
V.e = Vt * f
Ve = Minute Ventilation Vt = Tidal Volume f = Respiratory Frequency (breaths/min)
Why is alveolar (useful) ventilation different from minute ventilation?
Minute ventilation does not account for the volume of air that does not reach the respiratory zone.
What is the equation for alveolar ventilation?
V.a = (Vt-Vd) x f
V.a = Alveolar Ventilation Vt = Tidal Volume Vd = Dead Space Volume f = Respiratory Frequency (breaths/min)
