Short-term sympathetic baroreflex sensitivity increases at lower blood pressures.
OBJECTIVE
Sympathetic baroreflex sensitivity (symBRS) can be defined as the maximum sensitivity of muscle sympathetic nerve activity (MSNA) to changes in arterial blood pressure. This sensitivity is the slope of the linear middle part of the sigmoid curve that relates blood pressure to MSNA. SymBRS is known to vary with conditions, for instance during cold pressor testing. We investigated whether symBRS is affected by infusions of phenylephrine and nitroprusside.


METHODS
In 10 healthy subjects, vasoactive infusions were varied in slow steps, as customary in protocols to determine 'graded infusion symBRS' (symBRS(inf)). During each step, symBRS was estimated from spontaneous beat-to-beat fluctuations (symBRS(sp)). As a secondary goal, symBRS(inf) was compared to the symBRS(sp) without infusions.


RESULTS
The symBRS(sp) for MSNA burst area varied with infusions, augmenting with decreasing blood pressure, however the symBRS(sp) for burst occurrence was not affected. There were large differences between symBRS(inf) and symBRS(sp) at rest.


CONCLUSIONS
symBRS(sp) varies systematically with infusions during a symBRS(inf) protocol. This denotes a fundamental difference between these methods.


CONCLUSIONS
The relationship between 'slow' infusion effects (symBRS(inf)) and changes in symBRS(sp) is elucidated. The mathematical model that describes this relationship can also explain the increase of symBRS found with other sympathoexcitatory stimuli.
van Schelven
Leonard J
LJ
Department of Medical Technology and Clinical Physics, University Medical Center Utrecht, The Netherlands.
Karemaker
John M
JM
Blankestijn
Peter J
PJ
Oey
P Liam
PL
D000328:Adult; D017704:Baroreflex / Q000187:drug effects / Q000502:physiology*; D001794:Blood Pressure / Q000187:drug effects / Q000502:physiology*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D008962:Models, Theoretical; D009132:Muscles / Q000294:innervation; D009599:Nitroprusside / Q000494:pharmacology; D010656:Phenylephrine / Q000494:pharmacology; D013564:Sympathetic Nervous System / Q000187:drug effects / Q000502:physiology*; D013995:Time; D014662:Vasoconstrictor Agents / Q000494:pharmacology; D014665:Vasodilator Agents / Q000494:pharmacology
D014662:Vasoconstrictor Agents; D014665:Vasodilator Agents; D009599:Nitroprusside; D010656:Phenylephrine