Topographical distribution of pulmonary perfusion and ventilation, assessed by PET in supine and prone humans

Abstract

Using positron emission tomography (PET) and intravenously injected 13 N 2, we assessed the topographical distribution of pulmonary perfusion (Q˙) and ventilation (V˙) in six healthy, spontaneously breathing subjects in the supine and prone position. In this technique, the intrapulmonary distribution of 13 N 2, measured during a short apnea, is proportional to regional Q˙. After resumption of breathing, regional specific alveolar V˙(sV˙a, ventilation per unit of alveolar gas volume) can be calculated from the tracer washout rate. The PET scanner imaged 15 contiguous, 6-mm-thick, slices of lung. Vertical gradients ofQ˙ and sV˙a were computed by linear regression, and spatial heterogeneity was assessed from the squared coefficient of variation (CV 2). Both CV[Formula: see text] and CV[Formula: see text] were corrected for the estimated contribution of random imaging noise. We found that 1) both Q˙ and V˙ had vertical gradients favoring dependent lung regions, 2) vertical gradients were similar in the supine and prone position and explained, on average, 24% ofQ˙ heterogeneity and 8% of V˙ heterogeneity, 3) CV[Formula: see text] was similar in the supine and prone position, and 4) CV[Formula: see text] was lower in the prone position. We conclude that, in recumbent, spontaneously breathing humans, 1) vertical gradients favoring dependent lung regions explain a significant fraction of heterogeneity, especially ofQ˙, and 2) although Q˙ does not seem to be systematically more homogeneous in the prone position, differences in individual behaviors may make the prone position advantageous, in terms of V˙-to-Q˙ matching, in selected subjects.