First, as shown in Table 1 and Fig. 3, we found that for the traditional clinical figure-eight coil, the best magnetic stimulation effect of the cervical and thoracic sympathetic nerve could be obtained when the stimulation coil was placed 19mm beside the front side of the patient and fitted to the patient's neck as possible. Putting the stimulation coil on the back of the body is the worst magnetic stimulation towards our target area. This is because by comparing the data of groups 1a, 1b, 1c, and 1d, We found that the group 1a simulation produced the smallest induced current density on the sympathetic nerve chain in the human model while the induced current density produced on the spinal nerve chain is the largest (with the greatest side effects), and in the 1d group, the largest induced current density on the sympathetic nerve chain in the human model, The lowest induced current density generated on the spinal nerve chain is minimal (with the least side effects). By computational analysis of 1a, or 1d group data, We found that by changing the traditional site of figure-eight coil placement, You can increase the intensity of the sympathetic stimulation in the neck by about 3.98 times, Magnetic stimulation of the spinal nerve was reduced by about 49-times. With the support of this data analysis, we recommend clinicians to place the stimulation coil 19mm adjacent to the patient's neck as much as possible in the next stage of the clinical trial to obtain better experimental results.
Second, considering the data in Table 1 and Fig. 1, we found that large figure-eight coils (2a, 2b, 2c) had high stimulation intensity but poor focusing ability. When only considering the maximum induced current density data of the spinal and cervical othoracic sympathetic segments, we obtained the ratio of the maximum induced current density of the maximum cervical sympathetic chain in 2b simulations. That is, we believe that in the 2b group of simulation, we obtained the relatively optimal magnetic stimulation effect (with the least side effect versus the target area stimulation effect). However, as shown in the data of groups 2b and 2c in Table 1, we also found that due to the particularity of the neck structure, when the figure-eight coil size is too large, the coil is difficult to directly stimulate our target target area (and cervical and thoracic sympathetic nerve), which will reduce the stimulation intensity of the target area. Therefore, we recommend the researchers to explore the optimal size of the shape-eight coil for the sympathetic magnetic stimulation of the human cervical and thoracic segment in the next stage of their research.
Third, as shown in Fig. 2, we found the induction of electric field of the figure-eight coil decay along with the depth rapidly. And since the neck chest sympathetic nerve depth is about subcutaneous 27.89 ± 3.4mm[22], the figure-eight coil is not the best choice. Although the double conical coil can produce a greater depth of magnetic stimulation theoretically, the traditional double conical coil is difficult to fit closely with the human body due to the special structure of the human body neck. Hence, it is also difficult to obtain better experimental results. Therefore, in future experiments, we recommend that experimenters consider designing new neck coils that can reach deeper stimulation depth (for example, double-conical coil improvement according to the neck structure) to achieve better treatment results.
Fourth, we found this experiment is of great significance to the guidance and suggestions for the application of transcranial magnetic stimulation equipment to the sympathetic nerve in the neck. A clinical trial from 2003 showed that placing the figure-of-eight coil at the C6 to C7 spinous process on the back of the human body cannot effectively stimulate the sympathetic nerve[23]. Through our simulation experiments and the biomedical mechanism of sympathetic nerves and the effectiveness of magnetic stimulation in the peripheral nervous system, we believe that the results of this clinical experiment may be due to the improper placement of the coils, resulting in magnetic stimulation in the cervicothoracic sympathetic nerves. The stimulus intensity is minimal. We believe that in the next clinical trial, if the existing figure-of-eight transcranial magnetic stimulation coil is placed 19mm away from the anterior midline of the volunteer's neck, and it is as close as possible to the specific human neck structure, there may be obvious Effective effects of magnetic stimulation on the cervicothoracic sympathetic nerves were observed.
Finally, We found that the modeling results are of great significance in clinical applications. This study obtained more detailed and accurate data conclusions than clinical experiments through finite element simulation analysis, which is of great help for our research on the precision of control magnetoelectric intervention technology. At the same time, the study also reminds us that not only the treatment mode of magnetic stimulation or the sympathetic nerve, but other medical treatment plans, organs and regions can be simulated and analyzed in advance before clinical experiments. This allows research to be conducted more safely and efficiently to help advance medical science. Clinically, the result we want is a mild and effective intervention with magnetoelectric technology on the cervical sympathetic chain with important sympathetic ganglia, hoping to achieve sympathetic inhibition without puncture and non-invasive conditions. Research is our initial guide to designing such therapeutic devices.