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8 Cards in this Set

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  • Back
  • 3rd side (hint)
Alveolar Gas Equation
PAO2 = FlO2 x (Pb - PH2O) - PaCO2/R

R = respiratory quotient is generally about 0.8
Pb (atm) = 760mmHg
PH2O = 47mmHg (water moisture in mouth)
FlO2 = 21% if not augmented by supplement
This equation estimates the Alveolar O2 concentration from the measurable arterial O2 levels
Bohr Equation (Estimate Dead Space)
Vd/Vt = (PACO2 - PECO2) / (PACO2)

PACO2 is about equal to PaCO2. This is the case for CO2 but NOT O2
PECO2 - the expired CO2
Uses CO2 washout to measure indirectly the volume of the lungs
Alveolar Ventilation
PACO2 = PaCO2 = V'CO2 / (K*V'A)

V'A = alveolar ventilation is indirectly related to PaCO2
THis equation is important because it show how arterial CO2 is indirectly related to alveolar ventilation
double V'A and halve PaCO2
Minute Ventilate
Minute ventilation = Resp rate * tidal volume
Thus there are 2 ways to maintain the ventilation needed.
- alter resp rate
- alter tidal volume
Fick Equation
Flow Gas = [Area*(MW^0.5)*Solubility*Driving Pressure ] / (membrane thickness)
- Solubility (Higher = better flow) this is CO2
- Driving Pressure (O2 = 100 to 40 & CO2 = 40 to 45)
Each of these variables are manipulated for the lung to maximize gas transport
Laplaces Law (justify surfactant)
Pressure = 2T / R
R - radius
T - tension in the walls
Thus the small radii alveoli will require higher pressure to keep patent with equal tension
Compliance (elastance)
Compliance = dVolume / dPressure
Elastance is the inverse
Something compliant will increase volume easily for a given pressure.

Something with high elastance will require more pressure to increase its volume (it will be less compliant)
Respiratory Quotient
R = CO2 output / O2 input
R is usually 0.8
R changes based on anaerobic or aerobic metabolism
High fat diet will decrease CO2 output and the respiratory quotient