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COMPLEX FUNCTIONS OF THE CENTRAL NERVOUS SYSTEM, SLEEP AND LOCOMOTION

Relationship between blood pressure, sleep K-complexes, and muscle sympathetic nerve activity in humans

¹General Clinical Research Center, Syncope Service in the Autonomic Dysfunction Unit, and ³Department of Neurology, Vanderbilt University Medical Center, Nashville, Tennessee 37232; ²Clinical Research Center, Franz Volhard Clinic and Max Delbrück Center for Molecular Medicine, Helios-Kliniken Berlin, Medical Faculty of the Charité, Humboldt University, 13125 Berlin, Germany; ⁴Medicina Interna II, Ospedale L. Sacco, Milano 20157, Italy; and ⁵Division of Clinical Discovery, Pharmaceutical Research Institute, Bristol-Myers Squibb, Princeton, New Jersey 08543-4000

Submitted 8 January 2003 ; accepted in final form 7 March 2003

Stage 2 sleep is characterized by the EEG appearance of "K-complexes" and blood pressure oscillations. K-complexes may be directly related to blood pressure changes or they may reflect central sympathetic activation. We analyzed the temporal relationship among K-complexes, heart rate (HR), blood pressure (BP), and muscle sympathetic nerve activity (MSNA) during sleep in eight healthy volunteers (3 men and 5 women, age 22–41 yr). Most K-complexes presented as single large complexes (56 ± 20%), followed by single small complexes (15 ± 14%) and as couplets or triplets (13 ± 6%). Single large K-complexes were preceded by a baroreflex-mediated increase of MSNA in approximately one-half (55%) of the cases. Detailed analysis of HR, BP, and MSNA was possible in 63 (45%) large single K-complexes not disturbed by preceding baroreflex-related changes. Systolic and diastolic BP and MSNA increased significantly after single events (22.5 ± 13, 5.2 ± 2.1, and 6.5 ± 3.0%). Mean sympathetic baroreflex latency was similar after the single large K-complexes compared with the mean value during stage 2 sleep (1,290 ± 126 vs. 1,279 ± 61 ms). The area under the burst was significantly increased after single large K-complexes (median 3.9 vs. 9.0 arbitrary units, P < 0.03). The results support the hypothesis that K-complexes express cortical activation leading to temporary facilitation of sympathetic outflow in a graded fashion. Their functional effects appear to be independent of baroreflex modulation of MSNA in 50% of the cases.

cardiovascular physiology; autonomic nervous system; baroreflex

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