EFFECT OF SYMP NEURAL BLOCKADE ON REACTIVE HYPEREMIA & RESPONSES IN OSA

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This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. The purpose of this study is to better understand the role the sympathetic nervous system plays in the regulation of vascular tone in patients with obstructive sleep apnea (OSA). The specific aims of this protocol are to determine: 1) the maximal vasodilator capacity (reactive hyperemic blood flow response, RHBF); 2) the effects of sympathetic vasoconstrictor tone on RHBF; and 3) the effect of sympathetic vasoconstrictor tone on hypoxia-induced vasodilation in OSA. Based on preliminary data, we postulate that in OSA mechanisms of vasodilation are impaired. We further postulate that the reduced response to vasodilator stimuli is due to enhanced sympathetic tone. These aims will be addressed in 3 separate studies that employ similar techniques. In Study I we will determine RHBF in the arm and leg in OSA and in controls. In Study II we will determine the effect of regional forearm sympathetic blockade (Bier block, see below) on RHBF in OSA and in controls. In Study III we will determine the effect of the Bier block on forearm vasodilation induced by systemic hypoxia in OSA and in controls. Only one of the 3 studies will be performed in each subject on a given day. However, the subject may be invited to return on another day to participate in one of the other studies described above. To determine whether OSA therapy reverses vascular dysfunction, OSA patients will participate in the same study after 1-6 months of OSA treatment with continuous positive airway pressure therapy (CPAP).