SPONTANEOUS CARDIAC BARORECEPTOR REFLEX AND REGIONAL CIRCULATIONS IN CONSCIOUS RATS

Objective To determine the relationships between the activity of the s pontaneous cardiac baroreceptor reflex (BRX) and regional vascular dyn amics in conscious unrestrained rats. Design Simultaneous beat-to-beat recordings of blood pressure and measurements of indices of mesenteri c and hindquarters blood flows were performed in seven male normotensi ve conscious rats under baseline conditions during 1 h. Methods The re lationships between systolic blood pressure (SBP) and heart rate were examined using a computerized method, giving the degree of statistical dependence between values of the two parameters with the Z coefficien t, This analysis permitted detection of cardiac beats related to cardi ac BRX activity, Z analysis was also applied to SBP and to mesenteric or hindquarters blood flow or vascular resistance, Time-series represe ntations were used to describe the chronological patterns correspondin g to BRX spontaneous activity. Results In these rats, which presented spontaneous BRX-like patterns manifested by the Z analysis, BRX was ac tive during approximately 15% of the time, For 80% of these patterns, cardiac BRX acted to buffer falls in SBP. These depressor events were preceded by muscular vasodilations whereas vasodilations in the mesent ery were delayed, Z analysis of these spontaneous haemodynamic pattern s confirmed that muscular vasodilations were strongly associated with falls in SBP, whereas vasodilations lagged behind SBP by about seven b eats and were not dependent on simultaneous SBP values. Conclusions Th e Z method showed that spontaneous hindquarters vasodilations were ass ociated with cardiac BRX patterns and that mesenteric vasodilations we re not concomitant with falls in SBP and may be the consequence either of a delayed central response or of a local mechanism such as myogeni c autoregulation.