A 72-year-old man with CHF, paroxysmal nocturnal dyspnea, and orthopnea is referred for pulmonary function test in the supine and upright positions. Which of the following is higher at the apex of the lung than at the base when a person is upright?
a. Blood flow
b. Lung compliance
c. PaCO2
d. Ventilation
e. V/Q ratio