**Author details**

Valentina Ignatova

Clinic of Neurology, Multiprofile Hospital of Active Treatment, National Heart Hospital, Sofia, Bulgaria

\*Address all correspondence to: valyaig@abv.bg

© 2019 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
