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This Article Full Text Full Text (PDF) All Versions of this Article: 564/3/923    most recent jphysiol.2005.083352v1 Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Grant, D. A. Articles by Walker, A. M. Search for Related Content PubMed PubMed Citation Articles by Grant, D. A. Articles by Walker, A. M.

¹ Ritchie Centre for Baby Health Research, Monash Institute of Medical Research, Monash University, Clayton, Victoria, 3168, Australia
² Department of Human and General Physiology, University of Bologna, I-40127 Bologna, Italy

Autoregulation is a vital protective mechanism that maintains stable cerebral blood flow as cerebral perfusion pressure changes. We contrasted cerebral autoregulation across sleep–wake states, as little is known about its effectiveness during sleep. Newborn lambs (n= 9) were instrumented to measure cerebral blood flow (flow probe on the superior sagittal sinus) and cerebral perfusion pressure, then studied during active sleep (AS), quiet sleep (QS) and quiet wakefulness (QW). We generated cerebral autoregulation curves by inflating an occluder cuff around the brachiocephalic artery thereby lowering cerebral perfusion pressure. Baseline cerebral blood flow was higher (P < 0.05) and cerebral vascular resistance lower (P < 0.05) in AS than in QW (76 ± 8% and 133 ± 15%, respectively, of the AS value, mean ±S.D.) and in QS (66 ± 11% and 158 ± 30%). The autoregulation curve in AS differed from that in QS and QW in three key respects: firstly, the plateau was elevated relative to QS and QW (P < 0.05); secondly, the lower limit of the curve (breakpoint) was higher (P < 0.05) in AS (50 mmHg) than QS (45 mmHg); and thirdly, the slope of the descending limb below the breakpoint was greater (P < 0.05) in AS than QS (56% of AS) or QW (56% of AS). Although autoregulation functions in AS, the higher breakpoint and greater slope of the descending limb may place the brain at risk for vascular compromise should hypotension occur.

(Received 19 January 2005; accepted after revision 4 March 2005; first published online 10 March 2005)
Corresponding author A. M. Walker: Ritchie Centre for Baby Health Research, Monash Institute of Medical Research, Monash Medical Centre, 246 Clayton Road, Clayton, Melbourne, Victoria, 3168, Australia. Email: adrian.walker{at}med.monash.edu.au

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