Stewart J M, Erb M, Sorbera C
Department of Pediatrics, New York Medical College, Valhalla 10595, USA.
Pediatr Res. 1996 Nov;40(5):702-9. doi: 10.1203/00006450-199611000-00009.
Neurocardiogenic syncope may be caused by enhanced sympathetic activity evoking a vasodepressor-cardioinhibitory reflex. Heart rate variability (HRV) methods can be used to assess the modulation of sympathetic and parasympathetic activity. To determine whether HRV measurements are related to the outcome of head-up tilt testing (HUT), we studied 29 syncopal patients aged 7-19 y. After 30 min supine, patients were tilted to 80 degrees for 30 min or until syncope occurred. Sequential beats free from ectopy were analyzed. Time domain indices included SD (SDNN), root mean square successive differences (RMSSD), percent exceeding 50 ms (pNN50). An autoregressive model was used to calculate power spectra. Low frequency power (LFP, 0.05-0.15 Hz), high frequency power (HFP, 0.15-0.40 Hz), and total power (TP, 0.01-0.40 Hz) were compared before and after tilt. Data were obtained supine before tilt (baseline), within 5 min after HUT (early), 5-10 min after HUT (mid), and 15 min after HUT or presyncope (late). Seventeen patients fainted (HUT+), and 12 patients did not (HUT-). Variability indices were different for HUT- and HUT+ at baseline: SDNN was 123 +/- 17 versus 78 +/- 6, RMSSD was 127 +/- 23 versus 64 +/- 6 ms, pNN50 was 51 +/- 6 versus 31 +/- 4, respectively. Spectral data demonstrated decreased HFP and TP in HUT+ (834 +/- 133 and 2855 +/- 420 ms2) versus HUT- (3433 +/- 840 and 7062 +/- 1500). With tilt, SDNN, RMSSD, and pNN50 decreased proportionately in HUT- and HUT+. However, sympathovagal balance, measured by the ratio LFP/HFP and by normalized LFP, was markedly increased in HUT+ (2.2 +/- 0.7 and 0.43 +/- 0.03) compared with HUT- (0.8 +/- 0.2 and 0.31 +/- 0.02) at baseline and differences increased with tilt. With syncope, sympathetic activity decreased, and parasympathetic activity increased. Decreased RR variability with decreased parasympathetic activity and increased indices of sympathovagal balance before HUT predict a positive tilt test in children referred for evaluation of neurocardiogenic syncope.
神经心源性晕厥可能由增强的交感神经活动引发血管减压 - 心脏抑制反射所致。心率变异性（HRV）方法可用于评估交感神经和副交感神经活动的调节。为了确定HRV测量值是否与直立倾斜试验（HUT）的结果相关，我们研究了29名年龄在7至19岁的晕厥患者。仰卧30分钟后，患者被倾斜至80度持续30分钟或直至晕厥发生。对无异位搏动的连续心搏进行分析。时域指标包括标准差（SDNN）、逐次差值均方根（RMSSD）、超过50毫秒的百分比（pNN50）。使用自回归模型计算功率谱。比较倾斜前后的低频功率（LFP，0.05 - 0.15赫兹）、高频功率（HFP，0.15 - 0.40赫兹）和总功率（TP，0.01 - 0.40赫兹）。在倾斜前仰卧位（基线）、HUT后5分钟内（早期）、HUT后5 - 10分钟（中期）以及HUT后15分钟或接近晕厥时（晚期）获取数据。17名患者晕厥（HUT +），12名患者未晕厥（HUT -）。HUT - 和HUT + 在基线时的变异性指标不同：SDNN分别为123±17与78±6，RMSSD分别为127±23与64±6毫秒，pNN50分别为51±6与31±4。频谱数据显示，与HUT -（3433±840和7062±1500）相比，HUT +（834±133和2855±420毫秒²）的HFP和TP降低。随着倾斜，HUT - 和HUT + 中的SDNN、RMSSD和pNN50成比例下降。然而，通过LFP/HFP比值和标准化LFP测量的交感迷走神经平衡在基线时HUT +（2.2±0.7和0.43±0.03）显著高于HUT -（0.8±0.2和0.31±0.02），且随着倾斜差异增大。发生晕厥时，交感神经活动降低，副交感神经活动增强。在因神经心源性晕厥接受评估的儿童中，HUT前RR变异性降低、副交感神经活动减少以及交感迷走神经平衡指标增加预示倾斜试验结果为阳性。
