SYMPATHETIC CONTROL OF THE CEREBRAL CIRCULATION IN SLEEPING NEWBORN LAMBS

N. Loos², D. Grant¹, J. Wild¹, S. Paul¹, C. Barfield¹, A. Walker¹, 1 Ritchie Centre for Baby Health Research, Monash Institute of Reproduction and Development, Monash University, Clayton, Melbourne, Victoria, 3168, Australia, 2 Pole Genie Biomedical Perinatalite-Enfance, Universite de Picardie Jules Verne, ETPAPC (EA 2088), Faculte de Medecine, 3 rue des Louvels, 80036 Amiens cedex, France.

Active sleep (AS) is characterized by a tonic increase in cerebral blood flow (CBF) upon which are superimposed phasic increases in CBF associated with arterial blood pressure (Pa) surges, a decreases in cerebral vascular resistance (CVR) and an increase in extra-cerebral sympathetic nervous system (SNS) activation. Yet no study has systematically investigated the role of the SNS in regulating the cerebral circulation in sleep. We studied five newborn lambs undergoing spontaneous sleep-wake cycles before and after bilateral superior cervical ganglionectomy (SCG). Lambs were instrumented under general anesthesia (1.5% Halothane, 50% O₂, balance N₂O) to record CBF, Pa, intra-cranial pressure, cerebral perfusion pressure (Pcp = Pa-Pic) and CVR. 5 additional lambs acted as a sham-operated control group. A minimum of 72 hours post-operative recovery was allowed.

Prior to SCG, CBF was significantly higher in AS than in Quiet Wakefulness (QW) and Quiet Sleep (QS) (16.8 ± 0.8 ml/min, 14.1 ± 1.3 ml/min, 13.0 ± 1.2 ml/min respectively, one way repeated measures ANOVA, p ≤ 0.05). CBF increased significantly following SCG in tonic AS, QW and QS (32.9 ± 7.4%, 26.2 ± 13.7 %, and 27.3 ± 13.8 % respectively, [one way RM ANOVA, p ≤ 0.05 vs before SCG]), coincident with a decrease in CVR (-24.4 ± 2.4 %, -25.3 ± 7.7, and -26.9 ± 8.8, p ≤ 0.05). During the phasic surges of AS, CBF was higher and CVR was lower after SCG (one way ANOVA, p ≤ 0.05) although the magnitude of the surges did not change. No significant changes were observed in Pa or Pcp between pre- and post-SCG, nor was the sham control group affected by the surgery. We postulate that SNS protects the cerebral micro-vessels from pressure surges particularly during AS when the cerebral circulation is maximally dilated.