Cyclical fluctuations in blood pressure, heart rate and cerebral blood volume in preterm infants.

Many recently published papers describe cyclical changes of cerebral circulatory variables, mainly in cerebral blood flow velocity (CBFV) performed with Doppler sonography. In this paper we focus on another important variable of cerebral circulation: on cerebral blood volume (CBV) measured by near infrared spectrophotometry (NIRS). In a retrospective analysis of NIRS measurements in 20 preterm infants (median 27 3/7 weeks of gestation), the dominating frequencies and prevalence of cyclical changes of CBV and its possible correlation with peripheral circulatory variables (mean arterial pressure and heart rate) was examined. In 19 out of the 20 infants cyclical changes of CBV were found within a frequency range of 2-4.7 cycles/min which is comparable to the results of the Doppler studies describing fluctuations in CBFV. A dominating frequency of heart rate (HR), was found only in 12 out of 20 infants, and it was with 2.1-3.8 cycles/min in a similar range compared to CBV. In mean arterial blood pressure (MABP), however we detected cycles with longer periods every 1-2.5 min in 14 out of 20 infants. There was a significant coherence between MABP/CBV and HR/CBV. The area under the coherence curve, however, was significantly larger between MABP and CBV as compared to HR and CBV (P = 0.0007, Wilcoxon signed-rank test).