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This Article Full Text Full Text (PDF) All Versions of this Article: 583/3/1041    most recent jphysiol.2007.139204v1 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 Google Scholar Google Scholar Articles by Studinger, P. Articles by Taylor, J. A. Search for Related Content PubMed PubMed Citation Articles by Studinger, P. Articles by Taylor, J. A. Related Collections Cardiovascular

¹ Department of Physical Medicine and Rehabilitation, Harvard Medical School and Cardiovascular Research Laboratory, Spaulding Rehabilitation Hospital, 125 Nashua Street Boston, MA 02114, USA

According to conventional wisdom, hysteresis in cardiac vagal baroreflex function exhibits a specific pattern: pressure falls are associated with longer heart periods and a smaller linear gain. A similar pattern occurs in the pressure–diameter relationship of barosensory vessels, and therefore it has been suggested that baroreflex hysteresis derives solely from vascular behaviour. However, we hypothesized that mechanical and neural baroreflex components contribute equally to baroreflex hysteresis. Blood pressure, carotid diameter and the electrocardiogram were recorded continuously during two trials of sequential bolus injections of nitroprusside and phenylephrine in 14 young healthy subjects. Baroreflex gain and its mechanical and neural components were estimated for falls and rises in pressure and diameter. The position or set point of the relations was quantified at the mean pressure and mean diameter. Gains were determined via piecewise linear regression. Set points and gains for falls versus rises in pressure and diameter were compared with the Chow test. Hysteresis was observed in all individuals, but not in every trial. In most, but not all, trials pressure falls were associated with longer heart periods and smaller linear gain, as conventional wisdom would predict. However, the pattern of hysteresis derived from the interaction of both mechanical and neural components. The two components most often acted in opposition to determine differences in set point, but in conjunction to determine differences in baroreflex gain. Therefore, we conclude that hysteresis is not solely determined by barosensory vessel behaviour but by the complex interaction of mechanical and neural aspects of the arterial baroreflex.

(Received 21 June 2007; accepted after revision 13 July 2007; first published online 19 July 2007)
Corresponding author J. A. Taylor: Cardiovascular Research Laboratory, Spaulding Rehabilitation Hospital, 125 Nashua Street, Boston, MA 02114, USA. Email: jandrew_taylor{at}hms.harvard.edu