倾斜试验中晕厥患者自主神经功能的变化

Assessment of the changes in autonomic nervous function during head up tilt test in syncopal patients using spectral analysis of heart rate variability

目的 运用频谱法研究直立倾斜试验中血管性晕厥的发生机制。方法 对 2 7例不明原因晕厥患者行直立倾斜试验 ,运用频谱法计算低频 (LF)、高频 (HF)及LF/HF的变化。结果 15例发生晕厥或先兆晕厥 (阳性组 ) ,12例未出现症状 (阴性组 ) ,倾斜前两组LF、HF和LF/HF差异无显著性 ;阴性组倾斜后即刻HF明显下降 ,LF/HF显著升高 ,平卧后恢复到倾斜前水平 ,阳性组晕厥或先兆晕厥发作时 ,HF突然升高 (10 4 7± 4 0 4→ 32 95± 10 4 8) ,明显高于倾斜前 (2 3 4 4± 4 2 0→32 95± 10 4 8,P <0 0 5 ) ,LF/HF显著下降 (3 2 8± 0 39→ 1 0 7± 0 31,P <0 0 1) ,试验终止平卧后 ,HF和LF/HF恢复 ,两组LF在倾斜前后不同阶段均无明显变化。结论 在平卧、静息状态下 ,阳性患者和阴性患者的自主神经功能差异无显著性 ,倾斜后阳性患者迷走神经兴奋性在抑制过程中突然过度增强 ,导致晕厥或先兆晕厥发生。

Objective To study the pathological mechanism of vasovagal syncope, spectral analysis of heart rate variability was used to evaluate the changes of autonomic function during head up tilttest in patients with unexplained syncope.Methods 27 patients with recurrent episodes of unexplained syncope underwent 70° head up tilt test.Spectral analysis was used to assess the changes in autonomic function before tilt testing, immediately after tilting, just before the occurrence of syncope or at the end of the test, during the syncope period or at the end of the test and after testing in supine rest. At the same time, haemodynamic changes were recorded. Spectral power in very low frequency (VLF,0.003-0.04Hz), low frequency (LF, 0.04-0.15 Hz) and high frequency (HF, 0.15-2.00 Hz) were computed with Fast Fourier Transform analysis, and LF and HF were normalized: LF norm=100×LF/(TP-VLF) and HF norm=100×HF/( TP-VLF).Results 12 patients (mean age 40±10 years) showed a negative response and 15 patients (mean age 37±9 years) showed a positive response. Both systolic and diastolic blood pressure decreased in all the patients [(118.00±10.42→81.00±12.36) mm Hg, P <0.01 and (76.00±8.40→52.00±10.95) mm Hg, P <0.01] and heart rate decreased in 8 patients (53%). No significant difference in all the indices of spectral analysis was observed in supine position between the subjects with positive and negative test results. LF norm in both the groups did not alter during the entire tilt procedure. The decreased HF norm and increased LF/HF persisted throughout head up tilt test in the negative patients. In the positive patients, similar patterns of changes were observed before the occurrence of positive symptoms , and during the occurrence of the symptoms. HF norm abruptly rose (10.47±4.04→32.95±10.48) and obviously exceeded that before tilt testing (23.44±4.20→32.95±10.48, P <0.05) and LF/HF dropped (3.28±0.39→1.07±0.31, P <0.01).At supine rest just after test, all the indices in both groups came back.Conclusions In the supine position, autonomic function is similar between positive and negative subjects. Positive patients have a different pattern of response to the tilting test. The pathological mechanism leading to vasovagal syncope appears to be related with the abrupt and excessive increase of vagal activity.