212 MODULATION OF HEARTRATE BY THE ARTERIAL BARORECEPTOR REFLEX (ABR) IN NEONATES

Abstract

In contrast to the amount of literature available on ABR in human adults, there is little information referring to neonates. We studied 17 “healthy” neonates: median gestational age 29 wk. (P25-P75: 28-31.2), median postnatal age 5 d (P25-P75: 4-8), median birthweight 1125 g (P25-P75: 980-1775). Systolic bloodpressure (SBP) was 55±10 mmHg (mean±SD) and instantaneous heart period (IHP) 422±38 ms(mean±SD). Arterial bloodpressure(ABP) was recorded in a quiet behavioural state during two separate periods of 10 minutes on the same day. The ABP signal was extracted from an indwelling arterial catheter, used for routine monitoring of vital functions. The analysis of the ABP signal was performed off-line by means of a fully computerized algorithm. We calculated the standard deviation (SD) of IHP and SBP; this SD was used as a measure of the overall spontaneous variability. Spontaneous long-term SBP variability results in IHP variability (see figure). We used the ratio between SD of IHP and SD of SBP as an estimate for the ABR modulation of heart rate (ms/mmHg). No difference was found between the two separate periods (Wilcoxon test). The median ABR was 5.1 ms/mmHg (P25-P75: 3.4-9.1). We showed a statistical significant correlation between ABR and SBP (r=-0.63; p-=0.02) and between gestational age and SBP (r=0.64; p=0.02); no correlation was found between ABR and IHP or gestational age. Gestational age was not related to IHP. Conclusion: The ratio between SD of IHP and SBP is reproducible and is related to SBP. Our data suggest that the ratio between SD of IHP and SD of SBP is a valuable tool for estimating ABR in neonates.