Instantaneous Time-Courses of Baroreflex Sensitivity, Sympathetic and Vagal Activities in Response to Mueller Maneuver

We assessed, in 37 recordings of healthy volunteers, the effects induced by Mueller maneuver (MM) on the time-courses of the high frequency component of RR ( HF_{RR} ), the low frequency components of RR ( LF_{RR} ), systolic ( LF_{SBP} ) and diastolic blood pressure ( LF_{DBP} ), estimated by a time frequency distribution, and baroreflex sensitivity (BRS) computed by alpha index. Ensemble averages of indexes dynamics showed: SBP and DBP, after a fall in early strain ( S_{E} ), increased gradually in late strain ( S_{L} ), peaking in early post-strain ( PS_{E} ). Similarly, LF_{RR},\ LF_{SBP} and LF_{DBP} raised, but peaked in S_{L} , heart rate (HR) and LF_{RR}/HF_{RR} remained elevated through S_{E},\ S_{L} and PS_{E} All recovered gradually and fell below their baseline in late post strain ( PS_{L} ). BRS and HF_{RR} decreased during S_{E} and S_{L} and increased in PS_{L} , In S_{L} and PS_{L},\ LF_{SBP^{-}} SBP and LF_{DBP} -DBP correlations ranged from 0.60 to 0.83. MM induces, in S_{L} and PS_{E} . via the interaction of chemoreflex and baroreflex with reduced BRS, increments of sympathetic outflow and vagal withdrawal, effects associated to rising SBP, DBP, and HR; and, in PS_{L} , via baroreflex, now with augmented gain, evokes gradual reduction of sympathetic activity and increment of vagal outflow, leading to cardiodecelerative and hypotensive effects. This functional picture suggests that BRS changes possibly contribute to driving the autonomic cardiovascular response to MM.