INFLUENCE OF SLEEP STATE AND RESPIRATORY PATTERN ON CYCLICAL FLUCTUATIONS OF CEREBRAL BLOOD-FLOW VELOCITY IN HEALTHY PRETERM INFANTS

To examine the influence of sleep state, respiratory pattern, and vent ilation on cyclical fluctuations (CF) in cerebral blood flow (CBF) vel ocity (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 me asured using on-line pulsed Doppler ultrasound by insonating the middl e cerebral artery. Breathing was measured using a flow through system. The sleep state was monitored according to conventional criteria. Thr ee hundred and seventy-five epochs of 1 min each were analyzed; 207 du ring quiet sleep (QS) and 168 during rapid eye movement (REM) sleep. C Fs in CBFV were detected in all babies. The frequency of CF ranged fro m 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 m ean CBFV (cm/s) was similar in these two sleep states, the mean coeffi cient of variation, a measure of CF amplitude, was significantly highe r 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 pat terns, but the coefficient of variation was significantly higher in pe riodic and apneic patterns as compared with regular and irregular resp iratory 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), b ut not with the variability of the respiratory measurements. These fin dings suggest: (1) REM sleep is associated with a greater CBF variabil ity than QS, and (2) periodic and apneic breathing are associated with a greater CBF variability than regular or irregular breathing. We spe culate that sleep state and respiratory pattern do not determine but m odulate the CBF. Our data suggest that in studies involving interpreta tion of CBFV data using the Doppler technique, breathing patterns shou ld be taken into account in addition to sleep slate.