van Leeuwen P, Cysarz D, Lange S, Geue D, Groenemeyer D
Department of Biomagnetism, Grönemeyer Institute for Microtherapy, 44799 Bochum, Germany.
Chaos. 2007 Mar;17(1):015119. doi: 10.1063/1.2431703.
Fetal heart rate complexity was examined on the basis of RR interval time series obtained in the second and third trimester of pregnancy. In each fetal RR interval time series, short term beat-to-beat heart rate changes were coded in 8 bit binary sequences. Redundancies of the 2(8) different binary patterns were reduced by two different procedures. The complexity of these sequences was quantified using the approximate entropy (ApEn), resulting in discrete ApEn values which were used for classifying the sequences into 17 pattern sets. Also, the sequences were grouped into 20 pattern classes with respect to identity after rotation or inversion of the binary value. There was a specific, nonuniform distribution of the sequences in the pattern sets and this differed from the distribution found in surrogate data. In the course of gestation, the number of sequences increased in seven pattern sets, decreased in four and remained unchanged in six. Sequences that occurred less often over time, both regular and irregular, were characterized by patterns reflecting frequent beat-to-beat reversals in heart rate. They were also predominant in the surrogate data, suggesting that these patterns are associated with stochastic heart beat trains. Sequences that occurred more frequently over time were relatively rare in the surrogate data. Some of these sequences had a high degree of regularity and corresponded to prolonged heart rate accelerations or decelerations which may be associated with directed fetal activity or movement or baroreflex activity. Application of the pattern classes revealed that those sequences with a high degree of irregularity correspond to heart rate patterns resulting from complex physiological activity such as fetal breathing movements. The results suggest that the development of the autonomic nervous system and the emergence of fetal behavioral states lead to increases in not only irregular but also regular heart rate patterns. Using symbolic dynamics to examine the cardiovascular system may thus lead to new insight with respect to fetal development.
基于妊娠中期和晚期获得的RR间期时间序列来检查胎儿心率复杂性。在每个胎儿RR间期时间序列中，逐搏的短期心率变化被编码为8位二进制序列。通过两种不同的方法减少了2⁸种不同二进制模式的冗余度。使用近似熵（ApEn）对这些序列的复杂性进行量化，得到离散的ApEn值，这些值用于将序列分类为17个模式集。此外，根据二进制值旋转或反转后的一致性，将序列分组为20个模式类别。模式集中序列存在特定的、不均匀的分布，这与替代数据中的分布不同。在妊娠过程中，七个模式集中的序列数量增加，四个模式集中的序列数量减少，六个模式集中的序列数量保持不变。随着时间推移出现频率较低的序列，无论是规则的还是不规则的，其特征模式反映了心率的频繁逐搏反转。它们在替代数据中也占主导地位，表明这些模式与随机心跳序列相关。随着时间推移出现频率较高的序列在替代数据中相对较少。其中一些序列具有高度的规律性，对应于长时间的心率加速或减速，这可能与胎儿的定向活动或运动或压力反射活动有关。模式类别的应用表明，那些高度不规则的序列对应于由复杂生理活动如胎儿呼吸运动产生的心率模式。结果表明，自主神经系统的发育和胎儿行为状态的出现不仅导致不规则心率模式增加，也导致规则心率模式增加。因此，使用符号动力学来检查心血管系统可能会为胎儿发育带来新的见解。
