Influence of sleep state and respiratory pattern on cyclical fluctuations of cerebral blood flow velocity in healthy preterm infants.

Abstract

To examine the influence of sleep state, respiratory pattern, and ventilation on cyclical fluctuations (CF) in cerebral blood flow (CBF) velocity (CBFV), we studied 21 'healthy' preterm infants: birth weight 1,790 +/- 162 g (SEM), study weight 1,960 +/- 165 g, gestational age 32 +/- 1 weeks, postnatal age 20 +/- 4 (range 8-57) days. The CBFV was measured using on-line pulsed Doppler ultrasound by insonating the middle cerebral artery. Breathing was measured using a flow through system. The sleep state was monitored according to conventional criteria. Three hundred and seventy-five epochs of 1 min each were analyzed; 207 during quiet sleep (QS) and 168 during rapid eye movement (REM) sleep. CFs in CBFV were detected in all babies. The frequency of CF ranged from 0.5 to 6 cycles/min. The proportion of epochs showing CF was similar during both sleep states (56% QS vs. 59% REM; p = NS). Although the mean CBFV (cm/s) was similar in these two sleep states, the mean coefficient of variation, a measure of CF amplitude, was significantly higher during REM as compared with QS (6 +/- 0.5 vs. 4.3 +/- 0.2%; p < 0.05). Similarly, the mean CBFVs were similar with various respiratory patterns, but the coefficient of variation was significantly higher in periodic and apneic patterns as compared with regular and irregular respiratory patterns (5.6 +/- 0.6% periodic, 5.6 +/- 0.3% apneic, 3.6 +/- 0.3% regular, and 4.1 +/- 0.5% irregular, p < 0.05). The amplitude of CF was associated with the variability of the heart rate (p < 0.05), but not with the variability of the respiratory measurements. These findings suggest: (1) REM sleep is associated with a greater CBF variability than QS, and (2) periodic and apneic breathing are associated with a greater CBF variability than regular or irregular breathing. We speculate that sleep state and respiratory pattern do not determine but modulate the CBF. Our data suggest that in studies involving interpretation of CBFV data using the Doppler technique, breathing patterns should be taken into account in addition to sleep state.