Cardiac Autonomic Patterns Preceding Occasional Vasovagal Reactions in Healthy Humans

Abstract

Background-The wide range of clinical presentation of orthostatic vasovagal syncope suggests different underlying changes in the cardiac autonomic modulation. Methods and Results-To evaluate the beat-by-beat modifications in the neural control of heart period preceding a syncopal event, we studied RR interval variability in 22 healthy subjects who experienced fainting for the first time during a 90°head-up tilt and in 22 control subjects by means of time-variant power spectral analysis. Sympathetic and vagal modulations to the sinoatrial node were assessed by the normalized power of the low-frequency (LF, Ϸ0.1-Hz) and high-frequency (HF, Ϸ0.25-Hz) oscillatory components of RR variability. When the patients were supine, no differences were observed in the hemodynamic and spectral parameters of the 2 groups. During the tilt procedure, RR, LF NU , and HF NU (NUϭnormalized units) values were relatively stable in control subjects. During early tilt (T 1 ), subjects with syncope had reduced RR intervals compared with control subjects. In 13 subjects with syncope, RR decreased while LF NU and LF/HF increased in the last minute of tilt before syncope (T 2 ). Conversely, in the remaining 9 fainters, LF NU and LF/HF decreased from T 1 to T 2 and HF NU increased slightly. Conclusions-Two different patterns may be recognized in the cardiac autonomic changes preceding an occasional vasovagal event, namely, one characterized by a progressive increase of the marker of cardiac sympathetic modulation up to the onset of syncope, the other by a sympathetic inhibition with an impending vagal predominance. The recognition of different pathophysiological mechanisms in fainters may have important therapeutic implications.

Conditional symbolic analysis detects nonlinear influences of respiration on cardiovascular control in humans

“…This observation was corroborated by the dramatic drop of the HP variance reported in table 1. This pattern of response to the orthostatic challenge is frequently reported before syncope episodes induced by modification of posture [34].…”

On the feasibility of tilt test outcome early prediction using ECG and pressure parameters

“…Studies in literature based on spectral analysis did not improved early prediction of TTT outcome [7,8], although these studies provided significant contributions in terms of knowledge of the systems and mechanisms involved in syncope [15]. Power spectrum has been evaluated with parametric (auto-regressive [8,5]) and nonparametric methods (Fast Fourier Transform [7] and Wavelet [14]), yielding equivalent results.…”

“…In addition, the patient may feel very uncomfortable when the presyncopal or syncopal symptoms are reproduced. These problems have motivated the search for methods allowing the early prediction of the TTT [3][4][5][6][7][8][9][10][11][12][13][14][15][16]. The aim of these methods has often been to obtain a simple measurement, taken from an easily available cardiac signal (such as HR or pressure tachogram) at the beginning of the test, which would be used as a predictive criterion for the final result.…”

“…Other studies have analyzed the VVS in terms of the previously mentioned signals [5,[7][8][9]14], but did not focus on early prediction. Nevertheless, some recent studies have pointed out the difficulties that are found when the early prediction results are to be replicated in different patient databases.…”

Differences of Heart Rate Variability during Sevoflurane Anesthesia in Children by Age

“…Power spectral analysis of HRV is regarded as the index of autonomic nervous systemic regulation for sinus rhythm. [18,19] We calculated low-frequency (LFP) and high-frequency power (HFP) by integrating the power spectral density curve in the 0.04 -0.15 and 0.15 -0.4 Hz ranges. LFP is regarded as representative of activity of sympathetic and parasympathetic activity and HFP of the parasympathetic.…”