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

Using positron emission tomography (PET) and intravenously injected N-13(2), we assessed the topographical distribution of pulmonary perfusion ((Q) over dot) and ventilation ((V) over dot) in six healthy, spontaneously breathing subjects in the supine and prone position. In this technique, the intrapulmonary distribution of N-13(2), measured during a short apnea, is proportional to regional (Q) over dot. After resumption of breathing, regional specific alveolar (V) over dot (s(V) over dot 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 of (Q) over dot and s(V) over dot A were computed by linear regression, and spatial heterogeneity was assessed from the squared coefficient of variation 2). Both C (V) over dot (2)(Q) and CVs(s(V) over dot)(2) (A) were corrected for the estimated contribution of random imaging noise. We found that 1) both (Q) over dot and (V) over dot had vertical gradients favoring dependent lung regions, 2) vertical gradients were similar in the supine and prone position and explained, on average, 24% of (Q) over dot heterogeneity and 8% of (V) over dot heterogeneity, 3) CV(Q) over dot2 was similar in the supine and prone position, and 4) CVs(V) over dot A2 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 of (Q) over dot , and 2) although (Q) does not seem to be atically more homogeneous in the prone position, differences in individual behaviors may make the prone position advantageous, in terms of (V) over dot -to-(Q) over dot matching, in selected subjects.