Regional pulmonary perfusion, blood volume, and their relationship change during early ARDS in an experimental study

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 protective mechanical ventilation for 20 hours 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 hours, the animals’ 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. Early ARDS changed the relationship between F b and Q 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.