Physiologic Responses to Primary Blast

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Abstract
Primary blast injuries are produced by the blast shock wave. The critical determinant of survival is pulmonary injury, but acute cardiorespiratory responses to blast exposure are not well understood. The aim of this study was to investigate these changes. Twenty anesthetized rats were exposed to moderate blast overpressure, 10 animals receiving thoracic and 10 receiving abdominal exposure. Another 9 animals acted as controls. Respiration, heart rate, and blood pressure were recorded continuously before, during, and for 6 hours after blast exposure. All animals exposed to thoracic blast demonstrated apnea, bradycardia, and hypotension after blast exposure, followed by a return to preblast values. No significant cardiovascular or respiratory changes were seen in animals in the other groups. Moderate thoracic blast injury produces a reflex triad of apnea, bradycardia, and hypotension that is not present after abdominal blast. These observations may have important implications for the immediate management of patients with blast injuries.