Background

Traumatic or surgical hemorrhage causes substantial morbidity and mortality. Electrical vagus nerve stimulation (VNS) reduces traumatic hemorrhage in animal models. VNS targets acetylcholine-producing T lymphocytes in the spleen to increase intracellular calcium within circulating platelets via α7 nicotinic acetylcholine receptors. Elevated calcium levels facilitate platelet activation (priming) after tissue injury to accelerate and increase clot formation that improves hemostasis. Trigeminal nerve stimulation (TNS) also decreases traumatic hemorrhage in mice, but the mechanism remains unknown. Recently, we showed that transcutaneous auricular neurostimulation (tAN; combined auricular VNS and TNS) reduces blood loss and days of menstruation in women with idiopathic or von Willebrand disease related heavy menstrual bleeding. The ability of tAN or transcutaneous auricular VNS (taVNS) to improve platelet function or laboratory hemostasis remains unknown.

Methods

Here we performed a prospective, randomized, double-blind, sham-controlled, single-center, first-in-human exploratory trial to determine the safety and efficacy of taVNS or tAN to prime platelets and augment clot formation. Healthy adult subjects received sham stimulation before taVNS or tAN, followed by serial measurements of platelet and hemostasis markers, including platelet functional analysis, thrombin generation, blood counts, coagulation assays, and thromboelastography. Repeated measures one-way ANOVA followed by Bonferroni’s test was used for comparisons between three or more time points. Two-tailed paired T-test was used for comparisons between two time points.

Results

Administration of taVNS or tAN was well tolerated without observable adverse events during the study period. taVNS or tAN primed platelets via collagen- or ADP-mediated signaling pathways, respectively. taVNS accelerated clot initiation, propagation, and stabilization as measured by thromboelastography. There were no differences in systemic or local thrombin generation, circulating white or red blood cell counts, platelet counts, prothrombin time, partial thromboplastin time, or INR assays after administration of taVNS or tAN.

Conclusions

These results provide evidence that taVNS or tAN primes human platelets and taVNS accelerates clotting kinetics as quantified by thromboelastography. taVNS and tAN warrant additional clinical study as therapies for traumatic or surgical hemorrhage and congenital or acquired coagulopathies.