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 shock from blast wave injury. This study was a prospectively randomized, controlled animal study. Methods: By using a previously described model of blast wave injury, we randomized rats to one of four groups: control, blast-only, bilateral cervical vagotomy plus atropine 200 mu g/kg IP only, and bilateral cervical vagotomy plus atropine 200 mu g/kg IP before blast injury. Cardiopulmonary parameters were recorded for 90 minutes after the blast or until death. Results: Bradycardia, hypotension, and absence of compensatory peripheral vasoconstriction, typically seen in animals subjected to a blast pressure injury, were prevented by bilateral cervical vagotomy and intraperitoneal injection of atropine methyl-bromide. Hypoxia and lung injury were not statistically significant between the blasted groups, suggesting equivalent injury. Conclusion: Our data implicate a vagally mediated reflex such as the pulmonary defensive reflex as the cause of shock seen immediately after a blast pressure wave injury.