Airway resistance is determined by three major variables: gas viscosity, length of the airway, and radius of the airway.
Of these, the radius of the airway is the most impactful as it contributes to the fourth power in an inverse relationship with airway resistance (airway resistance will increase as radius decreases).
a) Resistance = 1/nl
b) Resistance = 8nl / pi*r^4
c) Resistance is directly proportional to airway radius
d) Resistance is inversely proportional to airway length
