Abstract â–¡ 120

It is assumed that deficiencies in the control of the respiratory system play an important part in a probably multifactor pathogenesis of life threatening events and sudden infant death. However, the determination of the variability of the breathing rhythm using statistical parameters, the incidence and length of apneas and other more have not proved to be useful for the prognosis of at-risk infants.

Years ago for the investigation of the periodic behavior. Recent studies, however hint on distinct nonlinear properties of respiration. A characteristic of non-linear systems is their complexity, which is caused by independently acting factors involved in autonomic systems. Complexity may be quantified by the calculation of the correlation dimension (D2).

In the present study, the postnatal development of the correlation dimension of the respiratory signal in healthy infants was investigated. Further, it was tested whether infants at risk differ regarding the complexity of respiration from a control group. The correlation dimension was calculated from the signal of the thoracic respiratory effort using the algorithm of Grassberger and Procaccia. To exclude an important influence of stochastic properties of the time series on the data analysis, surrogate data were calculated as suggested by Theiler et al.

D2 of the surrogate data was significantly higher in comparison with the original data in all groups. This means that the correlation dimension measures a nonlinear and deterministic property of the respiratory signal. D2 varied in all groups between 2 and 4 characterizing the respiratory system as low dimensional. During the postnatal period between birth and the sixth month of life, the correlation dimension showed a significant, biphasic course with an increase up to the end of the first month and following continuous decrease. Infants with bronchopulmonary dysplasia, who have an epidemiologically higher risk for SIDS, did not significantly differ in D2 from an age matched group of healthy controls.

The study presents at first time that complexity of respiration underlies a development after birth, which should be due to changes in the inputs into the system from several receptors as well as maturation of the central components. The interpretation of D2 in comparison of healthy with at-risk infants requires further studies regarding its physiological background and possible pathophysiological influences.