Shock after blast wave injury is caused by a vagally mediated reflex

Objective: Bomb blast survivors occasionally suffer from profound shock and hypoxemia without signs of external injury, We hypothesize that a vagally mediated reflex such as the pulmonary defensive reflex is the cause of shoc k from blast wave injury. This study was a prospectively randomized, contro lled animal study. Methods: By using a previously described model of blast wave injury, we ran domized rats to one of four groups: control, blast-only, bilateral cervical vagotomy plus atropine 200 mu g/kg IP only, and bilateral cervical vagotom y plus atropine 200 mu g/kg IP before blast injury. Cardiopulmonary paramet ers were recorded for 90 minutes after the blast or until death. Results: Bradycardia, hypotension, and absence of compensatory peripheral v asoconstriction, typically seen in animals subjected to a blast pressure in jury, were prevented by bilateral cervical vagotomy and intraperitoneal inj ection of atropine methyl-bromide. Hypoxia and lung injury were not statist ically significant between the blasted groups, suggesting equivalent injury . Conclusion: Our data implicate a vagally mediated reflex such as the pulmon ary defensive reflex as the cause of shock seen immediately after a blast p ressure wave injury.