Methodology of spontaneous baroreflex relationship assessed by surrogate data analysis

Abstract

We tested the hypothesis that the spontaneous beat-by-beat interactions of systolic blood pressure (SBP) and R-R interval reflected true baroreflex 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 [generated by a windowed (inverse) Fourier transform with phase randomization] and isodistribution (data points randomly shuffled) surrogate data sets. The isospectral data set was used to test for random phase relationships, and the isodistribution data set was used for effects of white noise between SBP and R-R interval. Spontaneous baroreflex sequences were defined as three or more beats in which SBP and the R-R interval of the same (lag 0), next (lag 1), or next following (lag 2) beat changed in the same direction. The total number of baroreflex sequences 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, these results indicated that spontaneous baroreflex sequences represented physiological rather than chance interactions and that baroreflex responses can occur within the same beat.

Investigating feedforward neural regulation of circulation from analysis of spontaneous arterial pressure and heart rate fluctuations in conscious rats

“…6) and as supported by previous studies (2). Therefore, according to the present and previous results (2,14), we conclude that lag 1 and 2 sequences can be considered as an expression of the feedforward neural mechanisms regulating the cardiovascular function, even though when HR is particularly high, as in conscious rats, the use of lag 5 sequences is reliable. It is noteworthy that both the hypertensive/tachycardic and the hypotensive/bradycardic sequences appear to be modulated by the sympathetic nervous system, inasmuch as both decreased significantly after sympathetic blockade.…”

“…However, lag 0 nonbaroreflex sequences seem to be, at least in part, modulated by the arterial baroreflexes as shown by their reduction in response to vagal blockade (see Fig. 6) and as supported by previous studies (2). Therefore, according to the present and previous results (2,14), we conclude that lag 1 and 2 sequences can be considered as an expression of the feedforward neural mechanisms regulating the cardiovascular function, even though when HR is particularly high, as in conscious rats, the use of lag 5 sequences is reliable.…”

Heart rate variability and spontaneous baroreflex sequences in supine healthy volunteers subjected to nasal positive airway pressure

“…Only episodes with correlation coefficients Ͼ0.95 were selected, and from all regressions a mean slope of baroreflex sensitivity was calculated for each steady-state period. By using isospectral and isodistribution surrogate data sets, Blaber et al (3) demonstrated that the sequences of interactions between BPsys and PI are real physiological events rather than chance interactions.…”

Autonomic circulatory and cerebrocortical responses during increasing depth of propofol sedation/hypnosis in humans

“…The technique of spontaneous baroreflex analysis was used to calculate sensitivity of the cardiac baroreflex. 17,18 The computer software examined each 15-min data recording to select all sequences of three or more successive heart beats in which there were concordant increases or decreases in systolic blood pressure (SBP) and RR intervals. A linear regression was applied to each of the sequences and an average regression slope was calculated for the sequences detected during each recording period.…”