Better quantification of neonatal respiratory sinus arrhythmia--progress by modelling and model-related physiological examinations.

A large interindividual variability of parameters quantifying respiratory sinus arrhythmia were found in a well defined group of healthy neonates during constant conditions of examination. Reasons for this can be found by means of a mathematical model which is based on physiological data. The results indicate sharp inconsistencies in the transfer function between respiratory movements and resulting respiratory sinus arrhythmia and are dependent on a relative frequency unit fN (ratio of mean respiration rate to mean heart rate). The values of the coherence (as a function of this relative frequency unit) between respiratory movements and heart rate are also distinguished by a systematic decrease from lower to higher fN values (fN = 0.1-0.5) and inconsistencies in modelling as well as in physiological examinations. The reasons for both effects can be demonstrated. The study is the basis of a new qualitative step of quantification of respiratory sinus arrhythmia in neonates by power spectral and coherence analyses.