DEVELOPMENT OF LINEAR AND NONLINEAR PROPERTIES OF HEART-RATE CONTROL DURING QUIET AND ACTIVE SLEEP IN HEALTHY INFANTS

In this study it is analyzed by linear and non-linear methods, how the control of instantaneous heart rate (IHR) develops in infants in quie t and active sleep. Ten healthy and term newborns were studied during their first half year of life. Low (LF) and high frequency power (HF) of the spectrum, and the largest Lyapunov exponent (LLE) were calculat ed from IHR. By means of the surrogate-data-test, significance of LLE with respect to linear correlated gaussian noise was verified. Signifi cant differences were determined between the original and the surrogat e data sets (p < 0.001) assuming non-linear properties. LF, HF, LLE ha ve irregular developmental patterns during the first month, whereby LL E has a distinct low value on the 21st day. HF significantly increases between the second and sixth month in quiet sleep, whereas for LF and LLE no significant correlations were found, neither for quiet nor act ive sleep. Using linear and non-linear methods, the study shows that t he system controlling heart rate pass through mainly two different dev elopmental periods: a period of adaptation in the first four weeks, wh ere parameters distinctly vary, followed by a period with clear develo pmental courses, lasting till the sixth month.