This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Respiratory system, Subject name: Physiology
Type of blood flow seen in the apex of the lung is 
Select and explain. 
A. No flow, P(ALV) > Ppc, B. Intermittent flow, P(ALV) < Ppc during diastole, C. Intermittent flow, P(ALV) < Ppc during systole, D. Continuous flow, P(ALV) < Ppc
C: Intermittent flow, P(ALV) < Ppc during systole
Answer: C: Intermittent flow, P(ALV) < Ppc during systole 
Explanation: Zone 2: Intermittent blood flow only during the peaks of pulmonary aerial pressure (Ppc) because the systolic pressure is then greater than the alveolar air pressure (PALV), but the diastolic pressure is less than the alveolar air pressure.