ORIGINAL ARTICLE Drosophila melanogaster Larvae as a Model for Blast Lung Injury Cameron R. Bass, PhD, Kevin P. Meyerhoff, MS, Andrew M. Damon, MS, Andrew M. Bellizzi, MD, Robert S. Salzar, PhD, and Karin A. Rafaels, BS Background: Primary blast injuries, specifically lung injuries, resulting from blast overpressure exposures are a major source of mortality for victims of blast events. However, existing pulmonary injury criteria are inappropriate for common exposure environments. This study uses Drosophila melano- gaster larvae to develop a simple phenomenological model for human pulmonary injury from primary blast exposure. Methods: Drosophila larvae were exposed to blast overpressures generated by a 5.1-cm internal diameter shock tube and their mortality was observed after the exposure. To establish mortality thresholds, a survival analysis was conducted using survival data and peak incident pressures. In addition, a histologic analysis was performed on the larvae to establish the mechanisms of blast injury. Results: The results of the survival analysis suggest that blast overpressure for 50% Drosophila survival is greater than human threshold lung injury and is similar to human 50% survival levels, in the range of overpressure durations tested (1–5 ms). A “parallel” analysis of the Bass et al. 50% human survival curves indicates that 50% Drosophila survival is equivalent to a human injury resulting in a 69% chance of survival. Histologic analysis of the blast-exposed larvae failed to demonstrate damage to the dorsal trunk of the tracheal system; however, the presence of flocculent material in the larvae body cavities and tracheas suggests tissue damage. Conclusions: This study shows that D. melanogaster survival can be correlated with large animal injury models to approximate a human blast lung injury tolerance. Within the range of durations tested, Drosophila larvae may be used as a simple model for blast injury. Key Words: Blast, Lung injury, Drosophila melanogaster. (J Trauma. 2010;69: 179 –184) T he most frequent injury attributed to terrorist attacks worldwide is blast trauma. 1 Historically, bombing inci- dents have been the most frequent type of terrorist attack 2 and explosive devices account for 79% of injuries sustained in the current military conflicts of Operation Iraqi Freedom and Operation Enduring Freedom. 3 The alveolar air spaces in the lungs are a common site of injury from blast exposure. 4 Drosophila melanogaster larvae have previously been used as an acoustic injury model to explore the injury mech- anisms and limits for human ultrasound and lithotripter exposures. 5–9 The respiratory system of a third instar D. melanogaster larva consists of a tracheal network that opens to the atmosphere at the spiracles. From the spiracles, air enters the dorsal trunks and then branches into smaller tra- cheal tubes throughout the organism. The main function of the Drosophila tracheal network is to transport oxygen to the tissues of the larva through passive diffusion. 10 If these struc- tures were damaged, as they may be when exposed to shock waves, ruptures of the surrounding cells could impede the diffusion of oxygen to cells throughout the larva, eventually causing death. Because a larval trachea and a human alveolus are similar in size, structure, and physiologic function, Drosoph- ila mortality may prove to be an acceptable model for human alveolar injury. This study will test the hypothesis that D. melanogaster larvae can be used as a model for human blast lung injury. It is predicted that 50% Drosophila survival will correlate with human threshold lung injury. To test this hypothesis, third instar Drosophila larvae will be exposed to shock waves and their corresponding survival values will be compared against existing human blast lung injury models. In addition, the mechanism of larval injury will be examined using a histo- logic analysis. MATERIALS AND METHODS Materials To establish mortality thresholds for D. melanogaster larvae, third instar larvae were exposed to a single shock wave produced by a 5.1-cm internal diameter shock tube. A schematic of the shock tube can be found in Figure 1. A removable section of the tube was used to load and unload the specimens during the tests. The shock waves were generating by detonating Winchester industrial loads 0.22 caliber shells (Winchester Ammunition, East Alton, IL), and the loads were varied to analyze a range of shock characteristics. The loads used were power level 4 yellow (model 22LRSC4), power level 6 purple (model 22LRSC6), and power level 7 gray (model 7LRSC). During testing, D. melanogaster specimens were held in a 2 cm  2 cm polypropylene mesh pouch with mesh opening dimensions of 0.53 mm  0.69 mm, and the mesh pouch was rigidly secured in a Petri dish. An Entran EPX- V01-100P 700 kPa pressure transducer (StrainSense Limited, Submitted for publication March 11, 2009. Accepted for publication September 30, 2009. Copyright © 2010 by Lippincott Williams & Wilkins From the Department of Biomedical Engineering (C.R.B.), Duke University, Durham, North Carolina; and Center for Applied Biomechanics (K.P.M., A.M.D., R.S.S., K.A.R.), Department of Mechanical and Aerospace Engineering, and Department of Pathology (A.M.B.), University of Virginia, Charlottesville, Virginia. Address for reprints: Andrew Damon, MS, Center for Applied Biomechanics, Department of Mechanical and Aerospace Engineering, University of Virginia, 1011 Linden Avenue, Charlottesville, VA 22902; email: amd3j@virginia.edu. DOI: 10.1097/TA.0b013e3181c42649 The Journal of TRAUMA ® Injury, Infection, and Critical Care • Volume 69, Number 1, July 2010 179