<Ul> <Li> apex of lung--higher </Li> <Li> base of lung--lower </Li> </Ul> <Li> apex of lung--higher </Li> <Li> base of lung--lower </Li> <P> In a subject standing in orthostatic position (upright) the apex of the lung shows higher V / Q ratio, while at the base of the lung the ratio is lower but nearer to the optimal value for reaching adequate blood oxygen concentrations . The main reason for lower V / Q ratios at the base is that both ventilation and perfusion increase when going from the apex to the base, but Q does it more strongly thus lowering the V / Q ratio . The principal factor involved in the genesis of V / Q dishomogeneity between the apex and the base of the lung is gravity (this is why V / Q ratios change in positions other than the orthostatic one). </P>

Which of the following conditions would affect the q portion of the v/q ratio