Abstract 8302: Lidocaine Abolishes the Sympathetic and Blood Pressure Responses in Limb Venous Distension Reflex

Abstract

Introduction- We have recently shown that saline infusion into the veins of an arterially occluded human forearm evokes a systemic response with an increase in muscle sympathetic nerve activity (MSNA) and blood pressure (BP). Hypothesis- Limb veins distension per se activates afferent nerves within (or close to) the vessel wall, and evokes a systemic sympathoexcitatory reflex. Methods- Thus, we examined MSNA and BP responses as albumin was infused into the venous circulation of an arterially occluded forearm. These MSNA and BP responses were compared with those seen with a saline infusion. Albumin preferentially remains within the vascular space whereas saline distributes within the entire limb extracellular space. BP (Finometer), heart rate, and MSNA (microneurography) were assessed in 14 young healthy subjects on 3 separate visits. In the saline trial, 5% forearm volume saline was infused into an arterially occluded arm. In the albumin trial (n=11), the same volume of albumin solution (5% concentration) was infused. In separate studies, 90 mg of lidocaine was added to the saline infusion (n=6). Results- MSNA and mean BP rose towards to the end of infusion in both saline and albumin trials. A larger (i.e. the peak response at the end of infusion: delta 14.3±2.7 vs. delta 8.5±1.3 bursts/min, P <0.01) and a sustained (i.e. the 30-60 sec of post infusion: delta 15.0±3.0 vs. delta 5.9±2.4 bursts/min, P <0.05) MSNA response was noted with albumin infusion as compared to saline infusion. The BP response with albumin infusion was also greater and sustained than saline infusion (all P <0.05). The 90 mg of lidocaine added to the saline infusion abolished >90% of the MSNA and BP responses. Discussion and Conclusion- These data suggest that vein distension is crucial to evoking the response seen. The lidocaine trial confirms that this venous distension evokes an autonomic reflex. We suggest that venous distension importantly contributes to autonomic and cardiovascular control in humans.