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1.  Is there evidence of fetal-maternal heart rate synchronization? 
BMC Physiology  2003;3:2.
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.
doi:10.1186/1472-6793-3-2
PMCID: PMC156603  PMID: 12702214
2.  Comparison of two different approaches in the detection of intermittent cardiorespiratory coordination during night sleep 
BMC Physiology  2002;2:18.
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.
doi:10.1186/1472-6793-2-18
PMCID: PMC140027  PMID: 12464159

Results 1-2 (2)