Limb venous distension evokes sympathetic activation via stimulation of the limb afferents in humans

Abstract

We have recently shown that a saline infusion in the veins of an arterially occluded human forearm evokes a systemic response with increases in muscle sympathetic nerve activity (MSNA) and blood pressure. In this report, we examined whether this response was a reflex that was due to venous distension. Blood pressure (Finometer), heart rate, and MSNA (microneurography) were assessed in 14 young healthy subjects. In the saline trial (n = 14), 5% forearm volume normal saline was infused in an arterially occluded arm. To block afferents in the limb, 90 mg of lidocaine were added to the same volume of saline in six subjects during a separate visit. To examine whether interstitial perfusion of normal saline alone induced the responses, the same volume of albumin solution (5% concentration) was infused in 11 subjects in separate studies. Lidocaine abolished the MSNA and blood pressure responses seen with saline infusion. Moreover, compared with the saline infusion, an albumin infusion induced a larger (MSNA: Δ14.3 ± 2.7 vs. Δ8.5 ± 1.3 bursts/min, P < 0.01) and more sustained MSNA and blood pressure responses. These data suggest that venous distension activates afferent nerves and evokes a powerful systemic sympathoexcitatory reflex. We posit that the venous distension plays an important role in evoking the autonomic adjustments seen with postural stress in human subjects.

Limb suction evoked during arterial occlusion causes systemic sympathetic activity in humans

“…Of note, a recent report by Yamauchi et al (33) has shown this reflex is also present in rats. Additionally, we have shown that venous infusion of albumin evokes a larger and more sustained increase in MSNA and BP than those with infusion of equal volume of saline (9). Albumin is a potent intravascular oncotic agent, and, thus, for a given volume, infusion of albumin should cause more distension than is seen with saline.…”

“…This protocol was performed in 13 subjects during a separate visit. The details of this protocol have been described in our previous reports (7)(8)(9). In brief, the forearm volume (i.e., from elbow to wrist) was assessed by water displacement before the instrumentation.…”

“…The magnitude of the MSNA and BP responses depends on the volume and the rate of the infusate during arm vein distension (8). When lidocaine is added to the forearm infusate, the MSNA and BP responses to venous distension are abolished (9). These observations clearly suggest that limb venous distension evokes a sympathoexcitatory reflex (termed venous distension reflex) and, thus, increases BP in humans.…”

“…Our recent reports (7)(8)(9)(10) have shown that volume infusion (saline or albumin solution, 5% forearm volume, ϳ50 ml) into the veins of an occluded forearm evokes reflex increases in muscle sympathetic nerve activity (MSNA) and BP in human subjects. The magnitude of the MSNA and BP responses depends on the volume and the rate of the infusate during arm vein distension (8).…”

“…Thus, we speculate that the major determinant of the response we have noted is the deformation of the vessels and/or pressure gradient generated across the vessels. It should be noted that all of these data regarding the venous distension reflex in humans (7)(8)(9)(10) and rats (33) were obtained with the volume infusion model. We speculate that it is necessary to develop a noninfusion approach to test the venous distension reflex.…”