Regional pulmonary perfusion, blood volume, and their relationship change in experimental early ARDS.

Regional pulmonary perfusion (Q) has been investigated using blood volume (F b ) imaging as an easier-to-measure surrogate. However, it is unclear if changing pulmonary conditions could affect their relationship. We hypothesized that vascular changes in early acute respiratory distress syndrome (ARDS) affect Q and F b differently. Five sheep were anesthetized and received lung protective mechanical ventilation for 20 h while endotoxin was continuously infused. Using dynamic 18 F-FDG and 13 NN Positron Emission Tomography (PET), regional F b and Q were analysed in 30 regions of interest (ROIs) and normalized by tissue content (F bn and Q n , respectively). After 20 h, the lung injury showed characteristics of early ARDS, including gas exchange and lung mechanics. PET images of F bn and Q n showed substantial differences between baseline and lung injury. Lung injury caused a significant change in the F bn -Q n relationship compared to baseline (p < 0.001). The best models at baseline and lung injury were F bn  = 0.32 + 0.690Q n and F bn  = 1.684Q n -0.538Q n 2 , respectively. Endotoxine-associated early ARDS changed the relationship between F b and Q, shifting from linear to curvilinear. Effects of endotoxin exposure on the vasoactive blood flow regulation were most likely the key factor for this change limiting the quantitative accuracy of F b imaging as a surrogate for regional Q.