Porta Alberto, Tobaldini Eleonora, Guzzetti Stefano, Furlan Raffaello, Montano Nicola, Gnecchi-Ruscone Tomaso
Dipartimento di Tecnologie per la Salute, Istituto Ortopedico Galeazzi, Laboratorio di Modellistica di Sistemi Complessi, Universita' degli Studi di Milano, Via R. Galeazzi 4, 20161 Milan, Italy.
Am J Physiol Heart Circ Physiol. 2007 Jul;293(1):H702-8. doi: 10.1152/ajpheart.00006.2007. Epub 2007 Feb 16.
Two symbolic indexes, the percentage of sequences characterized by three heart periods with no significant variations (0V%) and that with two significant unlike variations (2UV%), have been found to reflect changes in sympathetic and vagal modulations, respectively. We tested the hypothesis that symbolic indexes may track the gradual shift of the cardiac autonomic modulation during an incremental head-up tilt test. Symbolic analysis was carried out over heart period variability series (250 cardiac beats) derived from ECG recordings during a graded head-up tilt test (0, 15, 30, 45, 60, 75, and 90 degrees ) in 17 healthy subjects. The percentage of subjects showing a significant linear correlation (Spearman rank-order correlation) with tilt angles was utilized to evaluate the performance of symbolic analysis. Spectral analysis was carried out for comparison over the same series. 0V% progressively increased with tilt angles, whereas 2UV% gradually decreased. The decline of 2UV% was greater than the increase of 0V% at low tilt angles. Linear correlation with tilt angles was exhibited in a greater percentage of subjects for 0V% and 2UV% than for any spectral index. Our findings suggest that symbolic analysis performed better than spectral analysis and, thus, is a suitable methodology for assessment of the subtle changes of cardiac autonomic modulation induced by a graded head-up tilt test. Moreover, symbolic analysis indicates that the changes of cardiac sympathetic and vagal modulations observed during this protocol were reciprocal but characterized by different absolute magnitudes.
已发现两个符号指标，即具有三个无显著变化的心动周期的序列百分比（0V%）和具有两个显著不同变化的序列百分比（2UV%），分别反映交感神经和迷走神经调制的变化。我们检验了这样一个假设，即符号指标可能追踪递增式头高位倾斜试验期间心脏自主神经调制的逐渐变化。对17名健康受试者在分级头高位倾斜试验（0、15、30、45、60、75和90度）期间从心电图记录中获得的心动周期变异性序列（250个心搏）进行了符号分析。利用显示与倾斜角度有显著线性相关性（Spearman等级相关）的受试者百分比来评估符号分析的性能。对同一序列进行频谱分析以作比较。0V%随倾斜角度逐渐增加，而2UV%逐渐降低。在低倾斜角度时，2UV%的下降大于0V%的增加。与倾斜角度呈线性相关的受试者中，0V%和2UV%的比例高于任何频谱指标。我们的研究结果表明，符号分析比频谱分析表现更好，因此是评估分级头高位倾斜试验引起的心脏自主神经调制细微变化的合适方法。此外，符号分析表明，在此方案中观察到的心脏交感神经和迷走神经调制变化是相互的，但具有不同的绝对幅度。
