Observations and speculations on perfusion patterns in apparently normal lung scans

The patterns of pulmonary blood flow have been studied in 21 apparently normal perfusion scans. Two patterns were identified, a predominantly lower lobar distribution and a more even pattern. The predominantly lower lobar distribution is probably the more normal pattern, which suggests that in addition to the relationships between alveolar pressure, pulmonary vascular pressures and gravity, the anatomical structure of the lung also influences the regional distribution of blood flow. West's zone I was identified in 20 of the patients and occupied, on average, 16% of the vertical height of the lung. It is suggested that recognition of this zone may enable mean pulmonary arterial pressure to be measured from a combination of ventilation-perfusion imaging and the chest radiograph.