Dexmedetomidine for Reversal of Cocaine's Effects on the Heart

This study will use myocardial contrast echocardiography performed during a continuous intravenous infusion of Definity microbubbles (Perflutren lipid microbubbles) to determine if dexmedetomidine (an intravenous central sympatholytic drug) can reverse all the cardiovascular effects of low-dose intranasal cocaine-including vasoconstriction in the coronary microcirculation-both in cocaine-naïve and non-treatment seeking cocaine-addicted subjects.