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document
Yohimbine in neurally mediated syncope . Pathophysiological implications . In this study , we evaluated if increased sympathetic stimulation is an essential requirement for the development of neurally mediated syncope ( NMS ) by manipulating overall sympathetic outflow in subjects susceptible to tilt-induced syncope . Eight previously characterized patients with recurrent NMS ( five females and three males ; 34+/-2 yr ) were recruited from the Vanderbilt Syncope Unit and eight age-matched controls underwent initial administration of clonidine ( CLO ) or yohimbine ( YHO ) . This was done , prospectively , to determine doses of these agents that would increase or decrease plasma norepinephrine levels by > /= 30 % . On a different day , in all subjects we determined intraarterial blood pressure , EKG and muscle sympathetic nerve activity ( MSNA ) both supine and during upright tilt . After this , subjects randomly received either CLO or YHO , and 3 h later another tilt was performed . After 1 wk , a similar procedure with the other drug was performed . During the two basal tilts , all the control subjects completed the study , whereas all the NMS patients developed syncope . Reduction in sympathetic tone by CLO resulted in a decreased tolerance to tilt in three out of eight controls and in all the NMS patients . In contrast , YHO not only increased basal plasma NorEpi levels and MSNA , but also prevented syncope in seven out of eight patients . In a selected population of patients , increased sympathetic activity is not a prerequisite for the development of syncope . Yohimbine-induced enhancement of sympathetic tone in patients with NMS improves orthostatic tolerance and raises the possibility that this drug may be a useful agent in the treatment of NMS .
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Intervention_Pharmacological
Yohimbine
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Intervention_Pharmacological
clonidine ( CLO )
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Intervention_Pharmacological
yohimbine
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Intervention_Pharmacological
CLO
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Intervention_Pharmacological
YHO
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Intervention_Pharmacological
CLO
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Outcome_Physical
plasma norepinephrine levels
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Outcome_Physical
intraarterial blood pressure , EKG and muscle sympathetic nerve activity ( MSNA )
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Outcome_Physical
Reduction in sympathetic tone
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Outcome_Physical
tolerance to tilt
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Outcome_Physical
basal plasma NorEpi levels
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Outcome_Physical
MSNA
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Outcome_Physical
syncope
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Outcome_Physical
sympathetic activity
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Participant_Condition
neurally mediated syncope
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Participant_Condition
subjects susceptible to tilt-induced syncope
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Participant_Sample-size
Eight
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Participant_Sample-size
five
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Participant_Sex
females
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Participant_Sample-size
three
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Participant_Sex
males
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Participant_Age
34+/-2 yr
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Participant_Sample-size
eight
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Participant_Age
age-matched
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Participant_Condition
controls