Hypervolemic hyperalgesia in healthy young adults.

A cardiopulmonary baroreflex mechanism may be implicated in hypertensive hypoalgesia. Previous research in animals and humans has noted that manipulations that stimulate the vagus nerve are associated with predominantly anti-nociceptive effects. This study examined the effects of cardiopulmonary baroreceptor stimulation on venipuncture and intraveneous catherization pain during euvolemic and hypervolemic conditions while participants lay supine. In the euvolemic condition, participants maintained their normal diet whereas in the hypervolemic condition, they consumed additional water containing sodium citrate. As expected, blood volume was higher (P < .05) during the hypervolemic condition than the hypovolemic condition. Pain ratings were higher (P < .05) during hypervolemia compared to euvolemia. These findings suggest that increased cardiopulmonary baroreceptor activation during hypervolemia can be associated with increased sensitivity to noxious stimulation. In agreement with previously reported pro-nociceptive effects of vagus nerve stimulation, the current hyperalgesia finding provides further evidence that the cardiovascular system can influence the pain system.