AJP - Regulatory, Integrative and Comparative Physiology, Vol 273, Issue 2 540-R547, Copyright © 1997 by American Physiological Society
Linear and nonlinear properties of heart rate control in infants at risk
A. Patzak, B. Schluter, W. Orlow, R. Mrowka, D. Gerhardt, E. Schubert, P. B. Persson, D. Barschdorff and E. Trowitzsch
Institut fur Physiologie, Universitatsklinikum Charite, Humboldt-Universitat zu Berlin, Germany.
The aim of this study was to test whether the heart rate (HR) control in
infants at risk differs in comparison with healthy infants. Twelve former
preterm infants suffering from bronchopulmonary dysplasia and 18 control
infants, matched for their postconceptional age, were examined
polygraphically during quiet and active sleep. HR, low-frequency (LF)
power, high-frequency (HF) power, total power, and the ratio of LF to HF
power (LF/HF) of the instantaneous HR spectra were calculated for linear
analysis. The largest Lyapunov exponent (LLE) of the R-R interval time
series was calculated to determine a nonlinear property of HR. Infants at
risk had significantly lower LF power (median: 0.51 x 10(-3) vs. 1.16 x
10(-3) Hz2) and lower LF/HF (median: 1.05 vs. 1.94) during quiet sleep. LLE
was positive, revealing low-dimensional chaotic behavior of HR control, and
did not differ between both groups (median: quiet sleep, 0.05 bit/s vs.
0.06 bit/s; active sleep, 0.16 bit/s vs. 0.15 bit/s). Sleep state-related
changes in spectral parameters and LLE were similar in both groups. In
infants at risk, the lower LF/HF during quiet sleep can be interpreted in
terms of changes in the rhythmic components of the sympathovagal balance of
the autonomic system, which is an expression of linear properties of HR
control. Conversely, the lack of differences in LLE between both groups
indicates similar nonlinear properties of the control system.
