Abstract
Therapeutic applications of auricular vagus nerve stimulation (VNS) have drawn recent attention. Since the targeted stimulation process and parameters depend on the electrode–tissue interaction, the lack of structural anatomical information on innervation and vascularization of the auricle restrain the current optimization of stimulation paradigms. For the first time, we employed high-resolution episcopic imaging (HREM) to generate histologic volume data from donated human cadaver ears. Optimal parameters for specimen preparation were evaluated. Anatomical 3D vascular and nerve structures were reconstructed in one sample of an auricular cymba conchae (CC). The feasibility of HREM to visualize anatomical structures was assessed in that diameters, occupied areas, volumes, and mutual distances between auricular arteries, nerves, and veins were registered. The selected region of CC (3 × 5.5 mm) showed in its cross-sections 21.7 ± 2.7 (mean ± standard deviation) arteries and 14.66 ± 2.74 nerve fibers. Identified nerve diameters were 33.66 ± 21.71 μm, and arteries had diameters in the range of 71.58 ± 80.70 μm. The respective occupied area showed a share of, on average, 2.71% and 0.3% for arteries and nerves, respectively, and similar volume occupancy for arteries and nerves. Inter-centroid minimum distance between arteries and nerves was 274 ± 222 μm. The density of vessels and nerves around a point within CC on a given grid was assessed, showing that 50% of all vessels and nerves were found in a radial distance of 1.6–1.8 mm from any of these points, which is strategically relevant when using stimulation needles in the auricle for excitation of nerves. HREM seems suitable for anatomical studies of the human ear. A 3D model of CC was established in the micrometer scale, which forms the basis for future optimization of the auricular VNS. Obviously, the presented single cadaver study needs to be validated by additional anatomical data on the innervation and vascularization of the auricle.
Highlights
Auricular vagus nerve stimulation (VNS) is a new neuromodulatory technique for the treatment of, for instance, epilepsy (Bauer et al, 2016), chronic low back pain (SatorKatzenschlager et al, 2004), and psychiatric disorders like autism (Cimpianu et al, 2017)
The auricular VNS has some effects on cardiovascular system like suppressing atrial fibrillation (Stavrakis et al, 2015) and improving cardiac function in patients with coronary artery disease (Afanasiev et al, 2016), as summarized in our recent reviews (Kaniusas et al, 2019a,b)
The electrical stimulation of the peripheral branch of the auricular vagus nerve within the external ear provides an input to the brain stem and a noninvasive possibility to modulate various brain functions (Mercante et al, 2018)
Summary
Auricular vagus nerve stimulation (VNS) is a new neuromodulatory technique for the treatment of, for instance, epilepsy (Bauer et al, 2016), chronic low back pain (SatorKatzenschlager et al, 2004), and psychiatric disorders like autism (Cimpianu et al, 2017). The auricular VNS has some effects on cardiovascular system like suppressing atrial fibrillation (Stavrakis et al, 2015) and improving cardiac function in patients with coronary artery disease (Afanasiev et al, 2016), as summarized in our recent reviews (Kaniusas et al, 2019a,b). The electrical stimulation of the peripheral branch of the auricular vagus nerve (aVN) within the external ear provides an input to the brain stem and a noninvasive possibility to modulate various brain functions (Mercante et al, 2018). In pVNS, needle electrodes are placed in close vicinity to the visible vessels wired roughly in parallel to aVN, as identified by transillumination (Kaniusas et al, 2010)
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