METHODOLOGY OF SPONTANEOUS BAROREFLEX RELATIONSHIP ASSESSED BY SURROGATE DATA-ANALYSIS

We tested the hypothesis that the spontaneous beat-by-beat interaction s of systolic blood pressure (SEP) and R-R interval reflected true bar oreflex events rather than chance interactions. Original data sets of 1,024 heartbeats obtained in seated rest from six healthy subjects [R- R interval = 953 +/- 94 (+/-SE) ms] were compared with isospectral [ge nerated by a windowed (inverse) Fourier transform with phase randomiza tion] and isodistribution (data points randomly shuffled) surrogate da ta sets. The isospectral data set was used to test for random phase re lationships, and the isodistribution data set was used for effects of white noise between SEP and R-R interval. Spontaneous baroreflex seque nces were defined as three or more beats in which SEP and the R-R inte rval of the same (lag 0), next (lag 1), or next following (lag 2) beat changed in the same direction. The total number of baroreflex sequenc es in the original data was significantly greater than the surrogates (P < 0.001). In the original data, there were significantly (P < 0.001 ) more lag 0 than lag 1 or lag 2 baroreflex sequences. Therefore, thes e results indicated that spontaneous baroreflex sequences represented physiological rather than chance interactions and that baroreflex resp onses can occur within the same beat.