부정맥센터

Introduction: Syncope is defined as a sudden and transient loss of consciousness. Syncope can occur to any one, of whatever age, from the young to the elderly. In this study, we performed a head-up tilt test with isoproterenol provocation protocols, extracted heart rate variability (HRV) signals from the experimental subjects, and applied smoothed-pseudo Wigner-Ville distribution (SPWVD) time-frequency analysis (TFA) of HRV signals to analyse the dynamic changes to the autonomic nervous system (ANS). Previous research made a distinction between the power spectrum before and after the tilt test is performed on the experimental subjects. However, in this case, the response of ANS could not be differentiated, whether the subject took rest or had isoproternol provocation. For HRV signal analysis, the power spectrum was first estimated by Burg's maximum entropy AR method with an order of 30. LF and HF are used as indexes of sympathetic and parasympathetic activity, respectively. The normalized power is Ptotal and the PVLF are total power over 0 to 0.5 Hz, the VLF being the power component over 0 to 0.5 Hz. We used the Wigner-Ville distribution (WVD) function. To allow progressive and independent control in both time and frequency, a smoothed-pseudo Wigner-Ville (SPWV) distribution was used. Results and Discussion: The AR power spectrum shows only the spectral energy components, but TFA shows the continuous activities of sympathetic and parasympathetic nerve. The heart beat rate of subject is changed during the tilt test but any significant difference of the rate between the positive and normal groups was not observed. In the positive response and normal control groups, vagal activity was decreased before the syncope, sympathetic activity was increased. The difference of LFN or HFN between the negative response and normal control groups was not obvious. However, a significant difference of the LFN/HFN ratio existed between negative and normal response groups. We saw a dynamic change of LF and HF spectral components throughout the observational period as the HF component was continuously activating; thus it seemed to be affected by the respiratory centre of the subject. In our clinical experiments we found that patients with vasovagal syncope had normal resting autonomic tone as assessed by HRV indexes. However, the patients with syncope and a positive response from the tilt test had a difference response pattern from the normal control groups when the orthostatic stimulus was applied.