M5 Equations Flashcards
Alveolar Gas Equation
PAO2 = FIO2 (PATM – PH2O )– PaCO2 / RQ
Dead Space (Bohr Equation)
VD/VT = (PaCO2 –PECO2) / (Pa CO2)
Ohm’s Law
Pressure Gradient = Air Flow x Airway Resistance
Airway Resistance for Laminar Flow (Poiseuille’s Law)
Laminar Flow Resistance = (8 Length • Viscosity of gas) / (πRadius^4 )
Reynold’s Number
R = (Velocity x Density x Diameter) / (Viscosity)
> 2000 consistent with turbulent flow
Static Compliance
Static compliance = Volume/Pressure = (Tidal volume delivered) / (Plateau pressure – PEEP)
Dynamic Compliance
Dynamic compliance = Volume/Pressure = (Tidal volume delivered) / (Peak pressure – PEEP)
Law of LaPlace
Pressure = (2 • Wall Tension) / (Radius)
Note: wall thickness is typically not considered for alveoli
Transpulmonary Pressure
Transpulmonary pressure = Alveolar pressure – Pleural pressure
Transthoracic Pressure
Transthoracic pressure = Pleural pressure – Atmospheric pressure
Predicted PaO2 by Age
Predicted PaO2 = 110-(age • 0.4)
Boyle’s Law
Pressure1 • Volume1 = Pressure2 • Volume2
Ohm’s Law
Pressure = Cardiac Output • Resistance
Myocardial Perfusion Pressure
MPP = Aortic diastolic pressure – LVEDP
LaPlace Law
Tension = (Pressure • Radius)/(2 • Wall Thickness)
Note: Notice that as opposed to the equation in the Respiratory Section, the equation is solved for wall tension
Poiseuille’s Law
Flow Rate = (π • Pressure • radius4)/(8 • viscosity • length)
Note: Notice that as opposed to the equation in the Respiratory Section, the equation is solved for flow.
Fick Principle
CO = VO2/(CaO2 – CmvO2)
VO2 = Oxygen consumption CaO2 = Arterial content of oxygen CmvO2 = Mixed venous content of oxygen