Type of blood flow seen in the apex of the lung is: (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
Answer is C. 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.