Published Online
on March 12, 2007

A more recent version of this article appeared on May 1, 2007

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Submitted on November 8, 2006
Revised on November 24, 2006

To Dip or Not to Dip. On the Physiology of Blood Pressure Decrease During Nocturnal Sleep in Healthy Humans

Friedhelm Sayk; Christoph Becker; Christina Teckentrup; Horst-Lorenz Fehm; Jan Struck; Jens Peter Wellhoener; and Christoph Dodt^*

From the Clinic for Internal Medicine I, University Hospital of Schleswig-Holstein, Luebeck, Germany.

^* To whom correspondence should be addressed. E-mail: dodt{at}uni-luebeck.de.

Abstract--That sleep is accompanied by a blood pressure decrease is well known; however, the underlying physiology deserves further investigation. The present study examines in healthy subjects 2 main questions: is this dipping actively evoked? and what are the consequences of nondipping for daytime blood pressure? Nocturnal blood pressure was extrinsically elevated in 12 sleeping subjects to mean daytime values by continuously infused phenylephrine. This nondipping significantly lowered morning blood pressure during rest and 3 hours after resuming physical activity compared with a control condition (isotonic saline). Neither muscle sympathetic nerve activity nor sensitivity of -adrenoceptors was reduced. However, the set point for initiation of regulatory responses through the baroreflex was clearly shifted toward lower blood pressure levels. Our results support the hypothesis of an actively regulated central mechanism for blood pressure resetting and set point consolidation of the baroreflex during nighttime sleep. This is suggested by the fact that extrinsically induced nondipping induces sustained decrease in blood pressure during the following morning through an actively lowered baroreflex set point.

Key words: dipping • baroreflex • microneurography • MSNA • sympathovagal balance

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