PBF Changes In Areas Of Aspiration-Induced Acute Lung Injury Within Two Hours.

RATIONALE: Acid-aspiration is recognized as a risk factor for subsequent development of acute lung injury or ARDS. Areas of aspiration induced injury matches regions of high pulmonary blood flow (PBF) in the early stage of acute lung injury, as we shown recently. The aim this project was to characterize the changes of spatial PBF distribution as a function of time after injury.
METHODS: The protocol was approved by the Animal Studies Committee of the Landesdirektion Dresden. Eleven anesthetized, spontaneous breathing male Wistar rats were scanned with a small animal CT scanner before and after injury. Positron emission tomography (PET) was carried out after aspiration-induced lung injury. Aspiration was achieved by installation of 0.1 HCl (0.4 ml/kg body weight) through a tracheostomy tube. Pulmonary blood flow (PBF) was calculated from the radioactivity distribution in the lungs of infused 68Ga-DOTA-human serum albumin microspheres ten minutes after injury in group 1 (n=6) and two hours after injury in group 2 (n=5). CT- and PET images were co-registered. Areas of injury, as identified from CT derived changes in density, were labeled with a spherical mask. Regions of interest were derived using a threshold (80% of maximum) within the masks. Identical masks were used for the contralateral lung as reference. PBF was calculated and compared as a fraction of injured and reference side with Wilcoxon matched-pairs signed rank test. The PBF-fraction after the different time points was compared between the groups by unpaired t test with Welch's correction. RESULTS: Data presented are median (interquartile range). CT images after injury showed areas of lung injury different in size and location within the groups. Fraction of PBF was higher in group 1 (1.34 (1.15-1.45)) compared to group 2 (0.9 (0.85-1.06); P=0.0014) shown in Figure 1. The difference between both groups was determined by a high PBF in injured lung regions compared to the contralateral reference side at 10 min after injury (P = 0.03), whereas at 120 min after aspiration, injured regions have shown similar PBF compared to the contralateral reference side (0.81).
CONCLUSION: Regional PBF is increased 10 minutes after acid aspiration in regions of lung injury. This effect disappears within two hours after injury in anesthetized rats. These PBF-changes may be important for early treatment strategies after acid aspiration.