Journal of behavioral medicine
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Randomized Controlled Trial
The relationship between resting blood pressure and acute pain sensitivity: effects of chronic pain and alpha-2 adrenergic blockade.
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. ⋯ Significant Participant Type x 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.