1.3.3 Mechanism of Gas Exchange Flashcards
What is the equation for the pressure produced by a single gas?
Describe how partial pressure of gases combine to create a total pressure.
Ptotal = Pa + Pb
Find the partial pressures of gases a and b given that the Ptotal is 100 mm Hg; a, n=6 and b, n=14.
The air we breathe is a mixture of O2 and N2. In dry air, FO2 is ~ 21%, and N2 is ~ 79%
The total pressure is the barometric pressure, which at sea level it is 760 mmHg. Find the partial pressures of O2 and N2.
PO2 = 760 * 0.21 = 160 mm Hg
PN2 = 760 * 0.79 = 600 mm Hg
What must be subtracted from wet air to calculate the partial pressure of oxygen?
The partial pressure of water (PH2O) which is 47 mm Hg at 37 degrees celcius. This value is independent of the total pressure
At KUMC, PB =747. What is PIO2? (hint: this is wet air)
PIO2 = (747-47) * 0.21 = 147 mm Hg
The sum of the partial pressures of all gases must add up to what?
PB
What are the two ways to manipulate the partial pressure of a gas?
Changing total pressure (PB) or changing the concentration (FIO2)
What are the partial pressures of gases (O2, CO2, PAN2) in alveoli, veins, and arteries?
Describe how ventilation and blood flow affect O2 and CO2.
O2: Delivered by ventilation, removed by blood flow (metabolism)
CO2: delivered by blood flow (metabolism), removed by ventilation
Describe what hyper- and hypoventilation will do PAO2 and PACO2.
Hyperventilation: High PAO2, Low PACO2
Hypoventilation: Low PAO2, High PACO2
Describe the phases: pre-inspiration, inspiration, end-inspiration, and expiration. What does it mean that VE = VA + VD?
The equation, VE = VA + VD, refers to the fact that expired air is a composition of air that undergoes gas exchange in the alveoli and air that is trapped in dead space (doesn’t undergo exchange).
What causes the lag demarcated by the blue lines?
The lag is due to the dead space in the respiratory system where gas exchange doesn’t occur.
During expiration, what portion of gas can provide a good reflection of PAO2 and PACO2?
End tidal gas (air at the end of expiration)
What equation is beneficial for measuring gas exchange? What is the average value in a healthy individual?
VD/VE = (FACO2 - FECO2)/FACO2); 0.3
Doubling and halving ventilation will have what effect on FACO2?
Doubling of alveolar (not total) ventilation will halve PACO2 (and PaCO2); halving alveolar ventilation will double PACO2.
What is the alveolar gas equation?
PAO2 = PIO2 - (PACO2 * 1.2)