Binary symbolic dynamics classifies heart rate variability patterns linked to autonomic modulations.

Symbolic dynamics derived from heart rate variability (HRV) is able to reflect changes of cardiac autonomic modulations on short time scales in spite of the considerable reduction of information involved. However, the link between the appearance of specific symbolic patterns and the activity of the autonomic nervous system has not yet been elucidated. In this study, we investigate the symbolic dynamics that reflect acceleration (='1') and deceleration (='0') of the instantaneous heart rate. The resulting binary series is analyzed with respect to the regularity of binary patterns of length 8 using Approximate Entropy (ApEn). Binary patterns were grouped according to the level of their regularity as assessed by ApEn. ECG recordings were obtained from 17 healthy subjects during graded head-up tilt (0, 15, 30, 45, 60, 75, and 90°). The linear correlation (Spearman correlation coefficient) between tilt angle and the occurrence of binary patterns was evaluated. The results show that regular binary patterns occurred more often with increasing tilt angle whereas the occurrence of some irregular patterns decreased. Some binary patterns did not show a change of occurrence during tilt. When compared to the results of spectral analysis, regular binary patterns reflect sympathetic modulations whereas irregular binary patterns reflect parasympathetic modulations. The parameters derived from binary symbolic dynamics reflect changes of autonomic modulations during graded head-up tilt and are not fully correlated to the spectral markers of HRV.

Influence of paced maternal breathing on fetal-maternal heart rate coordination.

Pregnant mothers often report a special awareness of and bonding with their unborn child. Little is known about this relationship although it may offer potential for the assessment of the fetal condition. Recently we found evidence of short epochs of fetal-maternal heart rate synchronization under uncontrolled conditions with spontaneous maternal breathing. Here, we examine whether the occurrence of such epochs can be influenced by maternal respiratory arrhythmia induced by paced breathing at several different rates (10, 12, 15, and 20 cycles per minute). To test for such weak and nonstationary synchronizations among the fetal-maternal subsystems, we apply a multivariate synchronization analysis technique and test statistics based on twin surrogates. We find a clear increase in synchronization epochs mostly at high maternal respiratory rates in the original but not in the surrogate data. On the other hand, fewer epochs are found at low respiratory rates both in original and surrogate data. The results suggest that the fetal cardiac system seems to possess the capability to adjust its rate of activation in response to external--i.e., maternal--stimulation. Hence, the pregnant mothers' special awareness to the unborn child may also be reflected by fetal-maternal interaction of cardiac activity. Our approach opens up the chance to examine this interaction between independent but closely linked physiological systems.

Temporal asymmetries of short-term heart period variability are linked to autonomic regulation.

We exploit time reversibility analysis, checking the invariance of statistical features of a series after time reversal, to detect temporal asymmetries of short-term heart period variability series. Reversibility indexes were extracted from 22 healthy fetuses between 16th to 40th wk of gestation and from 17 healthy humans (aged 21 to 54, median=28) during graded head-up tilt with table inclination angles randomly selected inside the set {15, 30, 45, 60, 75, 90}. Irreversibility analysis showed that nonlinear dynamics observed in short-term heart period variability are mostly due to asymmetric patterns characterized by bradycardic runs shorter than tachycardic ones. These temporal asymmetries were 1) more likely over short temporal scales than over longer, dominant ones; 2) more frequent during the late period of pregnancy (from 25th to 40th week of gestation); 3) significantly present in healthy humans at rest in supine position; 4) more numerous during 75 and 90 degrees head-up tilt. Results suggest that asymmetric patterns observable in short-term heart period variability might be the result of a fully developed autonomic regulation and that an important shift of the sympathovagal balance toward sympathetic predominance (and vagal withdrawal) can increase their presence.

Quantification of fetal heart rate regularity using symbolic dynamics.

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.

[The effects of Cardiodoron on cardio-respiratory coordination--a literature review]. / Wirkung von Cardiodoron(R) auf die kardiorespiratorische Koordination - ein Literaturüberblick.

BACKGROUND: In healthy subjects self-regulation of the organism establishes the order of rhythmical functions. This self-regulation is altered in patients suffering from idiopathic orthostatic syndrome resulting from disturbances of functional aspects only. Thus the cardio-respiratory coordination, which may serve as the representative of the order of rhythmical functions, is modified. OBJECTIVE: In the case of idiopathic orthostatic syndrome the anthroposophic medicine offers the medicament Cardiodoron(r). Does it stimulate self-regulation in order to normalise the cardio-respiratory coordination? MATERIAL AND METHODS: This claim is analysed by a systematic review of the literature. Only those publications were considered where the cardio-respiratory coordination was analysed in studies with patients or healthy subjects. RESULTS: The methods of the studies with patients and healthy subjects vary strongly. Nevertheless, a normalisation of the cardio-respiratory coordination could be found in studies with patients suffering from idiopathic orthostatic syndrome as well as in studies with healthy subjects. CONCLUSION: The studies show that the use of the medicament results in a normalisation of the cardiorespiratory coordination. By stimulating the self-regulation the medicament leads to an improvement of the order of rhythmical functions in the human organism.

Bimodal dose-dependent effect on autonomic, cardiac control after oral administration of Atropa belladonna.

This single-blind placebo-controlled study was designed to investigate the dose-dependent vagolytic and vagotonic effects after a single oral administration of Atropa belladonna tincture (ABT, 0.1 mg/ml alkaloid concentration, atropine/scopolamine = 20:1). In eight healthy young subjects, heart rate and noninvasive arterial finger blood pressure were recorded simultaneously over 4 h after oral application of four different doses of ABT (day 1: 2 ml, day 2: placebo, day 3: 5 ml, day 4: 1 ml). On each day, 14 20-min sequences under controlled experimental conditions were performed. Among others, mean RR interval (RR), high-frequency spectral power of heart rate variability (HF), and noninvasive baroreflex sensitivity (BRS) were calculated during metronome breathing in supine position. These parameters were robust markers of vagal activity. One hour after 5ml ABT, RR, HF and BRS decreased clearly in six of eight subjects. This effect was interpreted as vagolytic response. After 1 and 2 ml ABT, and after placebo, RR and HF increased markedly. The increase after ABT was much higher than the increase solely due to adaptation after placebo administration, and it could be clearly identified as an augmentation of vagal cardiac activity caused by low-dose ABT. In conclusion, low doses of orally administered ABT can be effectively used to stimulate parasympathetic activity in man. The mode of vagal activation changes between 2 and 5 ml ABT from vagotonic to vagolytic. ABT has no or very little effect on blood pressure control.

Evaluation of modulations in heart rate variability caused by a composition of herbal extracts.

The purpose of this prospective, placebo-controlled, randomized double-blind study was the examination of changes of the basic vegetative rhythms due to Cardiodoron, a composition of extracts of blossoms from Primula officinalis and Onopordon acanthium and from the herbs of Hyoscyamus niger. In its clinical use it is known as a modulating medicine in the treatment of functional disturbances of the cardiovascular system. With use of Holter monitoring, 24-h ECG recordings were obtained from 100 healthy subjects of whom 50 took the composition and 50 a placebo. Heart rate variability was evaluated from the 24-h ECGs by means of a power spectral analysis based on the Fast Fourier Transformation (FFT). Regulative influences on the rhythmic system due to the medicine were found. After four weeks of medication half of the verum group showed a tendency to an increased variability in the low and high frequency range at night (LFn: 0.04-0.15 Hz, HFn: 0.15-0.4 Hz) in contrast to the placebo group. The mean heart rate at night (HRn) showed a tendency towards a normalization in the verum group: in subjects with a low HRn the heart rate was increased and in subjects with a high HRn the heart rate was decreased. This effect could not be observed in the placebo group. After two further weeks without any medication this difference between verum and placebo was abolished.

Entropies of short binary sequences in heart period dynamics.

Dynamic aspects of R-R intervals have often been analyzed by means of linear and nonlinear measures. The goal of this study was to analyze binary sequences, in which only the dynamic information is retained, by means of two different aspects of regularity. R-R interval sequences derived from 24-h electrocardiogram (ECG) recordings of 118 healthy subjects were converted to symbolic binary sequences that coded the beat-to-beat increase or decrease in the R-R interval. Shannon entropy was used to quantify the occurrence of short binary patterns (length N = 5) in binary sequences derived from 10-min intervals. The regularity of the short binary patterns was analyzed on the basis of approximate entropy (ApEn). ApEn had a linear dependence on mean R-R interval length, with increasing irregularity occurring at longer R-R interval length. Shannon entropy of the same sequences showed that the increase in irregularity is accompanied by a decrease in occurrence of some patterns. Taken together, these data indicate that irregular binary patterns are more probable when the mean R-R interval increases. The use of surrogate data confirmed a nonlinear component in the binary sequence. Analysis of two consecutive 24-h ECG recordings for each subject demonstrated good intraindividual reproducibility of the results. In conclusion, quantification of binary sequences derived from ECG recordings reveals properties that cannot be found using the full information of R-R interval sequences.

Musical rhythms in heart period dynamics: a cross-cultural and interdisciplinary approach to cardiac rhythms.

The purpose of this study was to expand classic heart period analysis methods by techniques from ethnomusicology that explicitly take complex musical rhythm principles into consideration. The methods used are based on the theory of African music, the theory of symbolic dynamics, and combinatorial theory. Heart period tachograms from 192 24-h electrocardiograms of 96 healthy subjects were transformed into binary symbol sequences that were interpretable as elementary rhythmic (percussive) patterns, the time lines in African music. Using a hierarchical rhythm pattern scheme closely related to the Derler Rhythm Classification (from jazz theory), we calculated the predominance and stability of pattern classes. The results show that during sleep certain classes, specific to individuals, occurred in a cyclically recurrent manner and many times more often than expected. Simultaneously, other classes disappeared more or less completely. Moreover, the most frequent classes obviously originate from phase-locking processes in autonomic regulation (e.g., between respiratory and cardiac cycles). In conclusion, the new interdisciplinary method presented here demonstrates that heart period patterns, in particular those occurring during night sleep, can be interpreted as musical rhythms. This method may be of great potential use in music therapy research.