Linear and nonlinear properties of heart rate control in infants at risk

Abstract

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.

Polysomnographic Reference Curves for the First and Second Year of Life . Perzentilkurven polysomnographischer Parameter fur das erste und zweite Lebensjahr

“…The percentile curves in figures 27 and 28 fit with data presented by other authors [20, 21, 32, 33, 46]. More sophisticated information can be obtained by calculation of heart rate variability [42 – 45].…”

“…In order to avoid distortions by small numbers, months 7 and 8, 9 and 10, 11 and 12, 13 to 24 and 25 and more, respectively, were grouped together. This is thought to be adequate, as age-related dynamics of polysomnographic parameters are known to be highest in the first six months of age, and less pronounced throughout the second half of the first year and afterwards [42][43][44]51]. Following parameters seemed to be normally distributed throughout the age range of 1 to > 24 months: total sleep time ( Because some polysomnographic parameters are not normally distributed, it is less appropriate to establish standards defined by the mean value of control subjects and the range from two standard deviations below to two standard deviations above the mean as normal values.…”

“…This can be attributed to several reasons. It is well known that the majority of cardiorespiratory parameters is strongly influenced by age, especially in the neonatal period [42][43][44][45] and during the first 6 months of life [51]. Thus, a very large data base has to be accumulated in order to calculate reference curves for these parameters.…”

Heart Rate Variability in Preterm Brain-Injured and Very-Low-Birth-Weight Infants

“…Although these techniques have considerable analytical power, our data were analyzed retrospectively and were not suitable for this type of analysis. We are also aware of nonlinear analysis techniques of HRV in neonates; however, to date, these techniques have not shown significant non-linearity in the age range in the present study [7,30].…”

“…Neonatal HRV patterns [6][7][8][9][10] are affected by gestational age [11,12], sleep state [13,14] and the severity of respiratory disease [12,15], and both mortality and morbidity from respiratory disease can be discriminated by the pattern of HRV [15,16]. Other reports have correlated HRV with neurodevelopmental test results at 8, 12, and 36 months of age in at-risk preterm infants [5,17].…”