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  • Title: Preserving cardiac output with beta-adrenergic receptor blockade and inhibiting the Bezold-Jarisch reflex during resuscitation from hemorrhage.
    Author: Wisbach G, Tobias S, Woodman R, Spalding A, Lockette W.
    Journal: J Trauma; 2007 Jul; 63(1):26-32. PubMed ID: 17622865.
    Abstract:
    BACKGROUND: Successful fluid resuscitation after severe hemorrhage may be limited by activation of the Bezold-Jarisch reflex. We postulated that pharmacologic inhibition of this reflex would restore cardiovascular hemodynamics more effectively than would volume repletion alone during resuscitation for hemorrhagic shock. METHODS: We measured mean arterial pressure (MAP), heart rate (HR), and cardiac output (CO) during fluid resuscitation after hemorrhaging laboratory rats until their CO had decreased by 90% to 95%. To block distinct components of the Bezold-Jarisch reflex, animals received capsazepine, yohimbine, or propranolol before iso-osmotic volume repletion. RESULTS: Hemorrhage decreased MAP and CO; despite an initial tachycardia, HR fell significantly in response to this large volume blood loss. The degree of hemorrhage-induced bradycardia mediated by the Bezold-Jarisch reflex predicted resuscitation MAP. Capsazepine-treated animals had greater resuscitation-induced increases in MAP (values in mm Hg +/- SEM), 130 +/- 12, when compared with the saline-only animals, 90 +/- 7 (p = 0.004). The capsazepine group also had a greater increase in systemic vascular resistance over baseline values during resuscitation (86% +/- 19%) compared with vehicle-treated animals (26% +/- 14%, p = 0.02). Capsazepine had no effect on cardiac dynamics. On the other hand, yohimbine increased HR and diminished CO, and propranolol dramatically increased stroke volume by 30%. CONCLUSION: Inhibition of the Bezold-Jarisch reflex may aid fluid resuscitation after hemorrhage only if stroke volume is restored. Beta-adrenergic receptor antagonists such as propranolol may prove the most salutary of these agents in enhancing fluid resuscitation in patients with severe hemorrhage.
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