The relationship between resting blood pressure and acute pain sensitivity: effects of chronic pain and alpha-2 adrenergic blockade |
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Authors: | Stephen Bruehl Ok Y Chung Laura Diedrich André Diedrich David Robertson |
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Institution: | (1) Department of Anesthesiology, Vanderbilt University School of Medicine, 701 Medical Arts Building, 1211 Twenty-First Avenue South, Nashville, TN 37212, USA;(2) Department of Medicine, Division of Clinical Pharmacology, Autonomic Dysfunction Center, Vanderbilt University School of Medicine, Nashville, TN, USA |
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Abstract: | This study tested for alpha-2 adrenergic mediation of the inverse relationship between resting blood pressure and acute pain
sensitivity in healthy individuals. It also replicated limited prior work suggesting this inverse blood pressure/pain association
is altered in chronic pain, and provided the first test of whether chronic pain-related changes in alpha-2 adrenergic function
contribute to these alterations. Resting blood pressure was assessed in 32 healthy controls and 24 chronic low back pain participants
prior to receiving placebo or an intravenous alpha-2 adrenergic receptor antagonist (yohimbine hydrochloride, 0.4 mg/kg) in
a randomized crossover design. Participants experienced three acute pain tasks during both sessions. A significant Systolic
Blood Pressure × Participant Type × Drug interaction on finger pressure McGill Pain Questionnaire-Sensory ratings (P < .05) reflected significant hyperalgesic effects of yohimbine in chronic pain participants with lower systolic blood pressures
(P < .05) but not those with higher systolic pressures, and no significant effects of yohimbine in controls regardless of blood
pressure level. A Drug × Systolic Blood Pressure interaction on finger pressure visual analog scale unpleasantness indicated
the inverse blood pressure/pain association was significantly stronger under yohimbine relative to placebo (P < .05). Significant Participant Type × Systolic Blood Pressure interactions (P’s < .05) were noted for finger pressure visual analog scale pain intensity and unpleasantness, ischemic pain threshold, and
heat pain threshold, reflecting absence or reversal of inverse blood pressure/pain associations in chronic pain participants.
Results suggest that blood pressure-related hypoalgesia can occur even when alpha-2 adrenergic systems are blocked. The possibility
of upregulated alpha-2 adrenergic inhibitory function in chronic pain patients with lower blood pressure warrants further
evaluation. |
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Keywords: | Blood pressure Pain Yohimbine Alpha-2 adrenergic Chronic pain Hypoalgesia |
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