Quantification of cyclical fluctuations in cerebral blood volume in healthy infants

Cyclical fluctuations in cerebral blood flow velocity in Doppler measurements are a well known phenomenon. In 1992 Livera et al have shown in one patient, that cyclical fluctuations of cerebral blood volume could be measured with near infrared spectroscopy (NIRS). The aim of the present study was a quantification of the amplitude of cyclical fluctuations of cerebral blood volume (represented by total haemoglobin [Hbtot]) in a large number of healthy infants. Furthermore changes of oxygenated haemoglobin (HbO2) and deoxygenated haemoglobin (Hb) were investigated. Measurements were done during two hours of undisturbed daytime sleep. Fifty-eight infants (30 male, 28 female) were included in the study. All but one infant showed cyclical fluctuations. For quantification of cyclical fluctuations only periods during quiet sleep with excellent tracing quality were used. A number of 7894 cycles was analyzed for each of the three NIRS parameters. The median amplitude of the cycling fluctuations was: delta Hbtot 1.1 mumol/l, delta HbO2 1.1 mumol/l, and delta Hb 0.2 mumol/l. The frequency was changing within a range of 3 to 6 cycles/minute. Polynominal regression analysis showed that the relationship of delta HbO2 and delta Hbtot was distinctively stronger compared to the relationship of delta Hb and delta Hbtot. In conclusion we think that these data represent "normal ranges" for parameter fluctuations in long-time NIRS tracings.