DYNAMIC CHANGES IN SPECTRAL HEART RATE VARIABILITY PARAMETERS IN PACED BREATHING TEST IN PATIENT WITH UNCONTROLLED ARTERIAL HYPERTENSION AND POLYMORBIDITY. J. V. N. Karazin Khark. Nat. Univ., Ser. Med. 2017;(32):73-78. doi:10.26565/2227-6505-2016-32-12