Central and baroreflex control of heart rate during the wake-sleep cycle in rat

Spontaneous fluctuations in Heart Period (HP) and Mean Arterial Pressure (M AP) make it possible to evaluate baroreceptor-heart rate reflex sensitivity (BRS). 30-s sequences of HP and MAP beat-to-beat values were considered in the different wake-sleep states (Wake, W; Quiet Sleep, QS; Active Sleep, A S) in rats to assess whether 1) BRS changes between states and 2) the diffe rent indexes supply consistent BRS measures, BRS indexes were calculated ac cording to validated literature procedures as regression coefficients of HP vs. MAP 1) within all ramps of increasing or decreasing MAP of four beats or more, with HP and MAP changing in the same direction (baroreflex-mediate d fluctuations, BRSP), 2) within all such ramps irrespective of the relativ e direction of HP and MAP changes (baroreflex + non-baroreflex, i.e. non-ho meostatic centrally driven, fluctuations, BRSA). HP vs. MAP regression coef ficient along the entire 30-s sequence (b(HPMAP)) was also calculated. Resu lts: BRSP did not change among states, BRSA decreased from QS to W to AS, b HPMAP decreased from QS to W and became negative in AS. Conclusions: 1) as indicated by BRSP, baroreflex sensitivity is state independent, 2) BRSP to BRSA to b(HPMAP) are increasingly affected by non-baroreflex fluctuations, BRSP being most apt to measure BRS, 3) non-homeostatic MAP and HP fluctuati ons increase from QS to W and prevail in AS. These potentially harmful fluc tuations are normally buffered by baroreflexes: in the case of baroreflex i mpairment, circulatory risk may arise in conditions like AS, when they prev ail.