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Title: A quantitative comparison of different methods to detect cardiorespiratory coordination during night-time sleep
Type: Article
Authors/Creators:
Cysarz D, Bettermann H, Lange S, Geue D & Van Leeuwen P
Source:
Biomed Eng Online 2004, 3(1): 44
Description:
Background: The univariate approaches used to analyze heart rate variability have recently been extended by several bivariate approaches with respect to cardiorespiratory coordination. Some approaches are explicitly based on mathematical models which investigate the synchronization between weakly coupled complex systems. Others use an heuristic approach, i.e. characteristic features of both time series, to develop appropriate bivariate methods. Objective: In this study six different methods used to analyze cardiorespiratory coordination have been quantitatively compared with respect to their performance (no. of sequences with cardiorespiratory coordination, no. of heart beats coordinated with respiration). Five of these approaches have been suggested in the recent literature whereas one method originates from older studies. Results: The methods were applied to the simultaneous recordings of an electrocardiogram and a respiratory trace of 20 healthy subjects during night-time sleep from 0:00 to 6:00. The best temporal resolution and the highest number of coordinated heart beats were obtained with the analysis of 'Phase Recurrences'. Apart from the oldest method, all methods showed similar qualitative results although the quantities varied between the different approaches. In contrast, the oldest method detected considerably fewer coordinated heart beats since it only used part of the maximum amount of information available in each recording. Conclusions: The method of 'Phase Recurrences' should be the method of choice for the detection of cardiorespiratory coordination since it offers the best temporal resolution and the highest number of coordinated sequences and heart beats. Excluding the oldest method, the results of the heuristic approaches may also be interpreted in terms of the mathematical models.
URL: http://www.biomedical-engineering-online.com/content/3/1/44
Year:
2004
Title: Oscillations of heart rate and respiration synchronize during poetry recitation
Type: Article
Authors/Creators:
Cysarz D, Von Bonin D, Lackner H, Heusser P, Moser M & Bettermann H
Source:
Am J Physiol Heart Circ Physiol 2004, 287: H579-H587
Description:
The objective of this study was to investigate the synchronization between low-frequency breathing patterns and respiratory sinus arrhythmia (RSA) of heart rate during guided recitation of poetry, i.e., recitation of hexameter verse from ancient Greek literature performed in a therapeutic setting. Twenty healthy volunteers performed three different types of exercises with respect to a cross-sectional comparison: 1) recitation of hexameter verse, 2) controlled breathing, and 3) spontaneous breathing. Each exercise was divided into three successive measurements: a 15-min baseline measurement (S1), 20 min of exercise, and a 15-min effect measurement (S2). Breathing patterns and RSA were derived from respiratory traces and electrocardiograms, respectively, which were recorded simultaneously using an ambulatory device. The synchronization was then quantified by the index, which has been adopted from the analysis of weakly coupled chaotic oscillators. During recitation of hexameter verse, was high, indicating prominent cardiorespiratory synchronization. The controlled breathing exercise showed cardiorespiratory synchronization to a lesser extent and all resting periods (S1 and S2) had even fewer cardiorespiratory synchronization. During spontaneous breathing, cardiorespiratory synchronization was minimal and hardly observable. The results were largely determined by the extent of a low-frequency component in the breathing oscillations that emerged from the design of hexameter recitation. In conclusion, recitation of hexameter verse exerts a strong influence on RSA by a prominent low-frequency component in the breathing pattern, generating a strong cardiorespiratory synchronization.
Year:
2004
Title: Is there evidence of fetal-maternal heart rate synchronization?
Type: Article
Authors/Creators:
Van Leeuwen P, Geue D, Lange S, Cysarz D, Bettermann H & Grönemeyer D
Source:
BMC Physiol 2003, 3: 2
Description:
Background: The prenatal condition offers a unique possibility of examining physiological interaction between individuals. Goal of this work was to look for evidence of coordination between fetal and maternal cardiac systems. Methods: 177 magnetocardiograms were recorded in 62 pregnancies (16th–42nd week of gestation). Fetal and maternal RR interval time series were constructed and the phases, i.e. the timing of the R peaks of one time series in relation to each RR interval of the other were determined. The distributions of these phases were examined and synchrograms were constructed for real and surrogate pairs of fetal and maternal data sets. Synchronization epochs were determined for defined n:m coupling ratios. Results: Differences between real and surrogate data could not be found with respect to number of synchronization epochs found (712 vs. 741), gestational age, subject, recording or n:m combination. There was however a preference for the occurrence of synchronization epochs in specific phases in real data not apparent in the surrogate for some n:m combinations. Conclusion: The results suggest that occasional coupling between fetal and maternal cardiac systems does occur
URL: http://www.biomedcentral.com/content/pdf/1472-6793-3-2.pdf
Year:
2003
Title: Effects of speech therapy with poetry on heart rate rhythmicity and cardiorespiratory coordination
Type: Article
Authors/Creators:
Bettermann H, Von Bonin D, Frühwirth M, Cysarz D & Moser M
Source:
Int J Cardiol 2002, 84(1): 77-88
Description:
Our objective was to study the effects of guided rhythmic speech with poetry, referred to as Anthroposophical Therapeutic Speech (ATS), on binary differential heart rate dynamics (also called musical heart rate rhythmicity or HRR) as well as on classical spectral parameters during the 15 minutes after speech exercise has ended. A total of 105 one-hour sessions with speech or control exercises were performed in 7 healthy subjects, with 15 sessions each. Heart rate was recorded with ambulatory solid state recorders. Sessions were divided into 15 minutes baseline measurement (S1), 30 mi nutes of exercise, and 15 minutes effect measurement (S2). The overall binary pattern predominance (PP) as well as the frequency of predominant and cyclically recurrent cardiorespiratory phase locking patterns were calculated from HRR and their changes from S1 to S2 were compared with the changes in low and high frequency heart rate variability. The results showed that: (1) ATS provokes alterations in heart rate dynamics which are different from those after control exercises and which persist at least for 15 minutes following exercise; (2) in comparison to spectral parameters of heart rate variability, pattern predominance discloses the effects of rhythmic speech exercises best; and (3) cardiorespiratory phase locking patterns, which contribute most to the rhythm pattern predominance, are more prominent after ATS.
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Year:
2002
Title: Comparison of two different approaches in the detection of intermittent cardiorespiratory coordination during night sleep
Type: Article
Authors/Creators:
Bettermann H, Cysarz D & Van Leeuwen P
Source:
BMC Physiol 2002, 2: 18
Description:
Background: The objective was to evaluate and to compare two completely different detection algorithms of intermittent (short-term) cardiorespiratory coordination during night sleep. The first method is based on a combination of respiratory flow and electrocardiogram recordings and determines the relative phases of R waves between successive onsets of inspiration. Intermittent phase coordination is defined as phase recurrence with accuracy α over at least k heartbeats. The second, recently introduced method utilizes only binary coded variations of heart rate (acceleration = 1, deceleration = 0) and identifies binary pattern classes which can be assigned to respiratory sinus arrhythmia (RSA). It is hypothesized that RSA pattern class recurrence over at least k heartbeats is strongly related with the intermittent phase coordination defined above. Results: Both methods were applied to night time recordings of 20 healthy subjects. In subjects <45 yrs and setting k = 3 and α = 0.03, the phase and RSA pattern recurrence were highly correlated. Furthermore, in most subjects the pattern predominance (PP) showed a pronounced oscillation which is most likely linked with the dynamics of sleep stages. However, the analysis of bivariate variation and the use of surrogate data suggest that short-term phase coordination mainly resulted from central adjustment of heart rate and respiratory rate rather than from real phase synchronization due to physiological interaction. Conclusion: Binary pattern analysis provides essential information on short-term phase recurrence and reflects nighttime sleep architecture, but is only weakly linked with true phase synchronization which is rare in physiological processes of man.
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URL: http://www.biomedcentral.com/content/pdf/1472-6793-2-18.pdf
Year:
2002
Title: Heart rate dynamics and cardiorespiratory coordination in diabetic and breast cancer patients
Type: Article
Authors/Creators:
Bettermann H, Kröz M, Girke M & Heckmann C
Source:
Clin Physiol 2001, 21(4): 411-420
Description:
Objective of this study was to evaluate cardiac autonomic function in female breast cancer patients on the basis of linear and nonlinear heart rate variability (HRV) as well as on musical heart rate rhythmicity. The latter method has been recently developed and enables particularly the quantification of cardiorespiratory coordination solely on the basis of ECG recordings. To provide a broad basis of comparability, 37 breast cancer patients were compared with 37 age-matched healthy women and 40 age-matched female diabetic patients who serve as pathological controls. During night sleep, all parameters showed a tendency towards lower variability, complexity, or rhythmicity of HRV in cancer patients. The most prominent alterations were found for the binary pattern predominance and for the ratio of heart rate and respiration. In particular, when comparing metastasized and non-metastasized cancer patients, the discriminatory power of binary heart rate rhythmicity emerges: the histograms of one-hour intervals during night sleep with a predominance of cyclically recurrent phase locking patterns unveiled a clear transition from higher to lower cardiorespiratory coordination ratios and to a loss of coordination capability in metastasized patients.
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Year:
2001
Title: Effects of an anthroposophical remedy on cardiorespiratory regulation
Type: Article
Authors/Creators:
Cysarz D, Heckmann C, Bettermann H & Kümmell HC
Source:
Altern Ther Health Med 2002, 8: 78-83
Year:
2002
Title: Bimodal dose-dependent effect on autonomic cardiac control after oral administration of Atropa belladonna
Type: Article
Authors/Creators:
Bettermann H, Cysarz D, Portsteffen A & Kümmell HC
Source:
Auton Neurosci (J Auton Nerv Syst) 2001, 90: 132-137
Description:
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 8 healthy young subjects, heart rate and noninvasive arterial finger blood pressure were recorded simultaneously over 4 h after oral application of 4 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 6 of 8 subjects. This effect was interpreted as vagolytic response. After 1 and 2ml 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.
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Year:
2001
Title: Irregularities and nonlinearities in fetal heart period time series in the course of pregnancy
Type: Article
Authors/Creators:
Cysarz D, Van Leeuwen P & Bettermann H
Source:
Herzschr Elektrophys 2000, 11: 179-183
Description:
Fetal heart rate variability reflects fetal development and is affected by pathological conditions. The aim of this study was to examine fetal heart period irregularity by focussing on nonlinear dynamical components. We recorded 165 fetal magnetocardiograms in 39 healthy pregnancies between the 16th and 41st week. The irregularity of the RR time series of each recording was quantified on the basis of the approximate entropy (ApEn). In order to estimate the nonlinear component, a surrogate time series was generated for each time series and ApEn was again calculated. Next, the purely dynamical aspect of the series was examined using a binary representation reflecting increase or decrease in RR interval of the original time series. ApEn of the original time series increased during pregnancy with a significant dependence on gestational age (p<0.0005). The ApEn values of the surrogate data increased similarly although the power of the relationship to week of gestation was weaker (roriginal=0.68, rsurrogate=0.46). Also the values of the surrogate series were generally higher, the mean difference being 0.24±0.24 (p<0.0005). ApEn of the binary series revealed no dependency on gestational age but again the values for the surrogate series were higher than those for the original series. The increase in irregularity of RR interval time series during pregnancy can be attributed in part to an irregular, nonlinear temporal structure and is not solely due to linear autocorrelations. Reducing information by constructing time series using binary symbolization which ignores the absolute beat durations resulted in a loss of dependency on gestational age but a retention of nonlinearity. The ability to quantify these processes promises to aid in prenatal risk stratification.
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Year:
2000
Title: The status of nonlinear dynamics in the analysis of heart rate variability (editorial)
Type: Editorial
Authors/Creators:
Van Leeuwen P & Bettermann H
Source:
Herzschr Elektrophys 2000, 11: 127-130
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Year:
2000
Title: Heart rate variability: How to assess effects of mild therapies on autonomic control in small groups of mild and borderline hypertensives?
Type: Letter
Authors/Creators:
Bettermann H, Cysarz D & Kümmell HC
Source:
Hypertension 2000, 35: e6-e7
Year:
2000
Title: Musikalischer Rhythmus im Herzschlag des Menschen
Type: Article
Authors/Creators:
Bettermann H
Source:
Medizin Individuell 2000, 2: 17
Year:
2000
Title: Evaluation of modulations in heart rate variability caused by a composition of herbal extracts
Type: Article
Authors/Creators:
Cysarz D, Schürholz T, Bettermann H & Kümmell HC
Source:
Arzneimittelforschung / Drug Research 2000, 50: 420-424
Year:
2000
Title: Entropies of short binary sequences in heart period dynamics
Type: Article
Authors/Creators:
Cysarz D, Bettermann H & Van Leeuwen P
Source:
Am J Physiol 2000, 278 (6) H2163-H2172
Description:
Dynamical aspects of RR 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 dynamical information is retained, by means of two different aspects of regularity. RR interval sequences derived from 24-hour ECG recordings of 118 healthy subjects were converted to symbolic binary sequences which coded the beat-to-beat increase or decrease in RR interval. Shannon entropy was used to quantify the occurrence of short binary patterns (length N=5) in binary sequences derived from 10-minute intervals. The regularity of the short binary patterns was analyzed on the basis of approximate entropy (ApEn). ApEn had a linear dependence on mean RR interval length, increasing irregularity occurring at longer RR interval length. Shannon entropy of the same sequences showed that the increase in irregularity is accompanied by a decrease of occurrence of some patterns. Taken together, this indicates that irregular binary patterns are more probable when the mean RR interval increases. The use of surrogate data confirmed a nonlinear component in the binary sequence. Analysis of two consecutive 24-hour 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 RR interval sequences.
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Year:
2000
Title: Detecting cardiorespiratory coordination by respiratory pattern analysis of heart period dynamics -- the musical rhythm approach
Type: Article
Authors/Creators:
Bettermann H, Cysarz D & Van Leeuwen P
Source:
Int J Bifurcation & Chaos 2000, 10(10), 2349-2360
Description:
The purpose of this study was to demonstrate that cardiorespiratory coordination can be unveiled by analyzing solely heart period data from the electrocardiogram (ECG). The analysis was done (1) on the basis of symbolic musical pattern analysis to detect intermittent cardiorespiratory phase coordination and (2) on the quantitative evaluation of respiratory sinus arrhythmia (RSA) to examine long-term frequency coordination between heartbeat and respiration. The methods were applied to 196 ECGs of 98 healthy subjects. The results showed that at night (1) intermittent phase coordination occurred reproducibly in individual subjects, and (2) long-term frequency ratios statistically approached 4:1 over all subjects to within an accuracy of 0.02, although individual values ranged from 2.5 – 6.0 with a high intraindividual reproducibility (r = 0.94, day A vs. day B). Moreover, intermittent phase coordination ratios and long-term frequency ratios corresponded to each other with a remarkably high correlation (r = 0.95). In the light of clinical applications, the coordination analysis presented here has an enormous advantage over those techniques depending on respiratory flow measurements, because the pattern technique requires only ECG recordings, and it is thus applicable over a longer period of time under daily life conditions.
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Year:
2000
Title: Presence of irregularity in fetal heart period time series
Type: Article
Authors/Creators:
Van Leeuwen P, Cysarz D & Bettermann H
Source:
Med Biol Eng Comput 1999, 37 Suppl. 2: 440-441
Year:
1999
Title: Musical rhythms in heart period dynamics -- A cross-cultural and interdisciplinary approach to cardiac rhythms
Type: Article
Authors/Creators:
Bettermann H, Amponsah D, Cysarz D & Van Leeuwen P
Source:
Am J Physiol 1999, 277 (5): H1762-H1770
Description:
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.
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URL: http://ajpheart.physiology.org/cgi/content/abstract/277/5/H1762
Year:
1999
Title: Magnetocardiography in the determination of fetal heart rate complexity
Type: Article
Authors/Creators:
Van Leeuwen P, Bettermann H, Schüssler M & Lange S
Publisher:
NY: Springer
Source:
In: Aine CJ, Okada Y, Stroink G, Swithenby SJ, Wood CC, eds. Biomag 96. Proceedings of the tenth international conference on Biomagnetism
Year:
1999
Title: Fetal heart rate variability and complexity in the course of pregnancy
Type: Article
Authors/Creators:
Van Leeuwen, Lange S, Bettermann H, Grönemeyer D & Hatzmann W
Source:
Early Hum Dev 1999, 54: 259-269
Year:
1999
Title: Hypertonie und Rhythmisches System: Erste Ergebnisse der Beobachtungsstudie
Type: Article
Authors/Creators:
Bettermann H & Kümmell HC
Publisher:
Bern: Peter Lang
Source:
In: Heusser P. (Hrsg.) Akademische Forschung in der Anthroposophischen Medizin. pp203-206
Year:
1999
Title: Zum Tagesgang der Atemfrequenz
Type: Article
Authors/Creators:
Heckmann C, Engelke P, Cysarz D, Bettermann H & Kümmell HC
Publisher:
Bern: Peter Lang
Source:
In: Heusser P. (Hrsg.) Akademische Forschung in der Anthroposophischen Medizin. pp139-147
Year:
1999
Title: Evidence of phase transitions in heart period dynamics
Type: Article
Authors/Creators:
Bettermann H & Van Leeuwen P
Source:
Biol Cybern 1998, 78: 63-70
Description:
Complexity measures of non-linear dynamics are a useful tool for quantifying observed stretching, folding, scaling and mixing processes in the Takens-reconstructed state space of heart period dynamics. Although such measures are not suited to provide evidence of deterministic chaos or to estimate true fractal dimensions and Lyapunov spectra in heart period time series, they allow the classification of RR dynamics and the identification of changes in RR complexity (RRC). The aim of this study was to develop appropriate measures and examine their utility in identifying the physiological effect of changes between the sleeping and waking state. Twenty-four hour electrocardiography (ECG) recordings and diaries noting their waking/sleeping period were obtained from 78 healthy subjects, aged 20 to 55 years. The approximate information dimension (ApD1) and the approximate Kolmogorov entropy (ApEn), introduced by Pincus, Kaplan and others, were modified in order to allow the calculation of strictly local values. That is, the local or pointwise dimensions and entropies were calculated for each reference vector with respect to its symmetric neighbourhood in time. For each subject the values for the local measures were averaged for 10-min periods, resulting in 144 global values over 24 h. Similarly, low- and high-frequency spectral parameters were calculated. All measures were examined and compared for the waking and the sleeping periods. All complexity measures as well as to a lesser degree high-frequency power showed a linear dependency on mean RR interval with a large individual variation. For the RRC measures this linear correlation was separated into two different clusters corresponding to the sleeping and waking periods. In almost all cases the correlation was greater in the waking period. In particular, in many cases no correlation was observed in the sleeping period. However, the r values for LF were appreciably lower and indicated solely a weak relationship to the RR interval in the waking period. Analysis of variance combining mean RR interval with RRC or spectral parameters singly and in couples revealed that the best separation with respect to physiological state could be achieved with the complexity measures, in particular with ApEn. The results show evidence of at least two dynamical regimes (phases) of heart period dynamics and a close but different functional relationship within the phases between RR interval and RR complexity. The separation between these regimes and the relatively sudden shift from one regime to the other suggest the existence of a phase transition with respect to waking and sleeping periods in terms of synergetics.
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Year:
1998
Title: Komplexitätsanalyse der fetalen Herzfrequenz -- Bestimmung der Dimension
Type: Article
Authors/Creators:
Lange S, Van Leeuwen P, Bettermann H & Grönemeyer D
Source:
Biomed Tech 1997, 42: (E1) 59-60
Year:
1997
Title: Gesteigerte LF-Herzperiodenvariabilität tagsüber nach 4-wöchiger Rehabilitation bei Patienten mit koronarer Herzkrankheit
Type: Article
Authors/Creators:
Bettermann H, Karoff M, Schulte M & Kümmell HC
Source:
Herz Kreislauf 1997, 29: 56-60
Year:
1997
Title: Die Bestimmung der Atemfrequenz aus der respiratorischen Sinusarrhythmie
Type: Article
Authors/Creators:
Bettermann H, Engelke P, Van Leeuwen P & Heckmann C
Source:
Biomed Tech 1996, 41 (11): 319-323
Description:
In der klinischen Praxis ist die Beobachtung ungestörter Spontanatmung und die Messung einer ‘unbeeinflußten’ Atemfrequenz praktisch unmöglich. Die über die respiratorische Sinusarrhythmie (RSA) elektrokardiographisch ermittelte Atemfrequenz bietet eine praktikable Alternative. In der vorliegenden Arbeit werden ein altes und ein neues Verfahren zur Atemfrequenzregistrierung aus dem EKG vorgestellt und miteinander verglichen. Das ältere bisherige Verfahren sucht ausgeprägte Maxima im atmungsrelevanten Bereich des Amplitudenspektrum einer 5-minütigen Zeitreihe der Momentanherzperiode (RR-Zeitreihe). Das neue Verfahren basiert auf einer Bandpassfilterung einer 1-minütigen RR-Zeitreihe und der anschließenden Analyse der Maxima, Minima und Nulldurchgänge der so ermittelten RSAAtemkurve. Zum Vergleich der Verfahren wurde die Atemfrequenz bei 16 männlichen Probanden unter 15 verschiedenen Versuchssituationen mit und ohne Taktatmung sowohl elektrokardiographisch als auch mit einem Atemthermistor direkt ermittelt. Die mittlere Abweichung vom direkt gemessenen Atemfrequenzwert lag für das bisherige Verfahren im Mittel bei 7,2 min-1, für das neue Verfahren bei 2,9 min-1. Nur bei Taktatmung 6 min-1 und Taktatmung 12 min-1 sitzend liefert das neue Verfahren ungenauere Atemfrequenzwerte. Die vorliegende Studie demonstriert die hohe Genauigkeit der aus der RSA-Atemkurve ermittelten mittleren Atemfrequenz. Das Verfahren erlaubt den Einsatz im klinischen Alltag und ermöglicht eine einfach zu realisierende Langzeit-Atemfrequenzregistrierung.
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Year:
1996
Title: Komplexitätsanalyse der RR-Dynamik im 24-Stunden-EKG -- Entwicklung, Visualisierung und Anwendung einer klinisch orientierten Chaosmetrie
Type: Dissertation
Authors/Creators:
Bettermann H
Publisher:
Egelsbach: Hänsel Hohenhausen
Source:
Deutsche Hochschulschriften Band 2316
Year:
1996
Title: Ergebnisse rhythmologischer Untersuchungen von Cardiodoron an Gesunden
Type: Article
Authors/Creators:
Kümmell HC & Bettermann H
Source:
Merkurstab 1996, 5: 361-371
Year:
1996
Title: Circadian aspects of apparent correlation dimension in human heart rate dynamics
Type: Article
Authors/Creators:
Van Leeuwen P, Bettermann H, An der Heiden U & Kümmell HC
Source:
Am J Physiol 1995, 269: H130-H134
Year:
1995
Title: Magnetokardiographie zur Erfassung fetaler Herzaktionen
Type: Article
Authors/Creators:
Van Leeuwen P, Schüssler M, Bettermann H, Lange S & Hatzmann W
Source:
Geburtshilfe, Frauenheilkunde 1995, 55
Year:
1995
Title: Magnetokardiographie zur Erfassung fetaler Herzaktionen
Type: Abstract
Authors/Creators:
Van Leeuwen P, Schüssler M & Bettermann H
Source:
Abstract in Z Kardiol 1994, 83 (9): 698
Year:
1994
Title: Dimensional analysis of RR dynamic in 24 hour electrocardiograms
Type: Article
Authors/Creators:
Bettermann H & Van Leeuwen P
Source:
Acta Biotheor 1992, 40 (4): 297-312
Year:
1992

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