Decreased Nonlinear Coupling of Peripheral Blood Volume to Heart Rate in Preterm Infants

Park, Eun Young; Kim, Chang Ryul; Yum, Myung Kul

Abstract

PURPOSE
We investigated the autonomic nervous and complex modulation of heart rate and peripheral blood volume, and linear and nonlinear coupling between heart rate and peripheral blood volume in full-term and preterm infants.
METHODS
In twenty healthy preterm infants and twenty full-term infants at postconceptional age of 30-37 and 38-41 weeks each, we recorded electrocardiogram and photoplethysmogram simultaneously during sleep in the supine position. To evaluate the autonomic and complex modulation, we performed power spectral analysis and analysis of the univariate nonlinear determinism. To quantify degree of linear and nonlinear couple between heart rates and peripheral blood volume, analyses of cross spectrum and bivariate nonlinear determinism were performed respectively.
RESULTS
In the analysis of heart rates, preterm infants had significantly lower normalized high-frequency power (20.3+/-7.7% vs 30.7+/-15.1%, P<0.05), higher low-to high-frequency power ratio (3.0+/-2.1 vs 1.9+/-1.6, P<0.05), and significantly lower univariate prediction error (2.9+/-1.3% vs 4.1+/- 2.8%, P<0.05) when compared to full-term infants. In the analysis of peripheral blood volume, they showed no significant differences. Cross spectrum in all frequency ranges showed no significant difference between them. But preterm infants showed a significantly higher bivariate nonlinear prediction error (4.8+/-3.8% vs 3.1+/-2.2%, P<0.05) and a lower statistical coupling index (16.6+/-10.4 vs 22.9+/-9.2, P<0.05) than full-term infants.
CONCLUSION
Compared to full-term infants, the heart rates of preterm infants are less modulated by cardiac parasympathetic activity and less complex. Furthermore, their peripheral blood volume was less nonlinearly coupled to heart rate.