Asymmetric detrended fluctuation analysis in neonatal stress

We aim at detecting stress in newborns by observing heart rate variability. Thanks to an asymmetric detrended fluctuation analysis (ADFA), we determine the fractal structure of the series of interbeat intervals, in which we distinguish the periods of acceleration of the heart rate from decelerations. Thus, two scaling exponents, α+ and α-, representing decelerations, and accelerations, respectively, are obtained. Forty healthy term newborns were included in this study, undergoing two different types of stress stimuli, using routine heel lance blood sampling for metabolic screening purposes and its simulation applying dull pressure on the heel. It appears that, when newborns face stress, the scaling exponent related to accelerations significantly increases and becomes higher than the deceleration scaling exponent. To test the diagnostic properties of the scaling exponents, a ROC curve analysis was applied. α- showed good diagnostic performance with an AUC of 0.826 and 0.796 respectively, although having a lower sensitivity, it showed a high specificity of 84.62% for both stress phases. This work thus stresses the relevance of ADFA and particularly of the acceleration scaling exponent as a diagnostic tool for neonatal stress.