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Journal of Peking University(Health Sciences) ›› 2019, Vol. 51 ›› Issue (3): 430-438. doi: 10.19723/j.issn.1671-167X.2019.03.009

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Prediction of syncope with nonlinear dynamic analysis during head-up tilt in vasovagal syncope patients

Fan LI1,Han-bin WANG2,Qing PENG1,Yun-chuang SUN1,Ran ZHANG2,Bo PANG2,Jing FANG2,Jue ZHANG2△(),Yi-ning HUANG1△()   

  1. 1. Department of Neurology, Peking University First Hospital, Beijing 100034, China
    2. Academy of Advanced Interdisciplinary Study, Peking University, Beijing 100871, China
  • Online:2019-06-18 Published:2019-06-26

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Abstract: Objective: To quantify the relationship between cerebral blood flow velocity and peripheral blood pressure during hypotension period, aiming to predict the brain hypotension before symptomatic occurrence.Methods: Twenty vasovagal syncope (VVS) patients who had a previous clinical history were selected in groups and 20 pair-matched control subjects underwent 70° tilt-up test. The subjects remained supine for 30 minutes before recordings when Doppler probes, electrodes and Finapres device were prepared. After continuous baseline recordings for 10 min, the subjects underwent head up tilt (HUT) test (70°), and were standing upright for 30 minutes or until syncope was imminent. For ethical reasons, the subjects were turned back to supine position immediately after SBP dropped to ≥20 mmHg, when their consciousness persisted. The point of syncope was synchronized for all the subjects by the point SBP reached the minima. Their beat-to-beat blood pressures (BP) were recorded continuously and bilateral middle cerebral artery (MCA) flow velocities were obtained with two 2 MHz Doppler probes from a transcranial Doppler ultrasonography (TCD) system. A nonlinear dynamic method——multimodal pressure flow (MMPF) analysis was introduced to access cerebral autoregulation during different time intervals. We introduced a new indicator——syncope index (SI), which was extracted from blood flow velocity (BFV) signal to evaluate the variation of cerebral vascular tension, and could reflect the deepness of dicrotic notch in BFV signal. Results: Compared with the syncope index of the baseline value at the beginning of the tilt test, SI in VVS group showed significantly lower when the VVS occurred (0.16±0.10 vs.0.27±0.10,P<0.01),while there was no significant difference in syncope index between the control group at the end of the tilt test and the baseline value at the beginning of the tilt test. For those VVS patients, pulse index and resistance index had no significant change. Syncope index decreased significantly 3 minutes before the point of syncope (0.23±0.07 vs.0.29±0.07,P<0.01).Conclusion: Dynamic regulation is exhausted when vasovagal syncope occurred. Tension decrease of small vessels could have some relationship with loss of the cerebral autoregulation capability. The proposed syncope index could be a useful parameter in predicting syncope of VVS patients since it decreased significantly up to 3 minutes earlier from the point of syncope.

Key words: Vasovagal syncope, Cerebral autoregulation, Nonlinear dynamics

CLC Number: 

  • R725.4

Table 1

Baseline characteristics of patients group and control group"

Parameter Patients Control group P
Number of subjects, n 20 20 NA
Age/years 39±12 (19-59) 37±19 (21-76) 0.71
Systolic blood pressure/mmHg 127±19 116±24 0.10
Diastolic blood pressure/ mmHg 75±13 68±13 0.08
Heart rate/(/min) 72±10 68±10 0.32
Mean blood flow velocity/(cm/s) 59±11 58±16 0.77

Figure 1

Dicrotic notch of a typical vasovagal syncope patient during different stage A, supine rest; B, immediate after tilt; C, before syncope point; D, in different stage: supine rest, black line; third last minute before return to supine, red line; second last minute before return to supine, green line; first last minute before return to supine, blue line. A, also showed systolic blood flow velocity(BFV), diastolic BFV and inflexion BFV, definition of pulse velocity and Dicrotic velocity."

Figure 2

Detection of dicrotic notch inflexion point using ensemble empirical mode decomposition A, raw blood flow signal, (+) indicates the detected inflection point; B, intrinsic modes for each component frequencies. The intrinsic mode in red were selected to detect inflexion point, and the inflexion point in the selected mode corresponded to the inflexion point in the raw blood flow velocity signal."

Figure 3

A typical patient fluctuation of blood pressure (BP), blood flow velocity (BFV) and syncope index (SI) during different stage of tilt A, BP and BFV fluctuation, dashed box are time interval from supine rest to second minute after tilt and from 3 minutes before syncope point to syncope point; B, SI during the process from supine rest to second minute after tilt; C, SI during the process from 3 minutes before syncope point to syncope point."

Figure 4

Syncope index reduction relative to baseline in different time periods A, syncope index reduction relative to baseline in control group; B, syncope index reduction relative to baseline in patients group. b, indicates duration of tilt; c, first minute after tilt; d, second minute after tilt; g, last minute before return to supine (vasovagal syncope group); h, Last minutes before the end of the tilt test (control group)."

Table 2

Comparison of physiological parameters between different time periods"

Patients Different time points in tilt test
d e f g
BP-BFV phase shift degree 59.6±20.6 20. 9±17.4# 21.0±12.3# 12.9±9.9#
Syncope index 0.29±0.07 0.23±0.07* 0.19±0.09# 0.16±0.10#
Pulse index 0.81±0.14 0.85±0.13 0.84±0.11 0.89±0.13*
Resistance index 0.52±0.05 0.54±0.05 0.54±0.04 0.55±0.05*

Figure 5

Syncope index, BP-BFV phase shift, pulse index, resistance index in different time period in VVS group A, syncope index; B, phase shift; C, pulse index; D, resistance index.a, indicates last minute before tilt (baseline); b, duration of tilt; c, first minute after tilt; d, indicates second minute after tilt; e, third last minute before return to supine; f, second last minute before return to supine; g, last minute before return to supine; Significant level:*P<0.05,# P<0.01."

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