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This Article Full Text Full Text (PDF) All Versions of this Article: 288/4/H1777    most recent 00594.2004v1 Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in ISI Web of Science Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via ISI Web of Science (14) Citing Articles via Google Scholar Google Scholar Articles by Nollo, G. Articles by Ravelli, F. Search for Related Content PubMed PubMed Citation Articles by Nollo, G. Articles by Ravelli, F.

Exploring directionality in spontaneous heart period and systolic pressure variability interactions in humans: implications in the evaluation of baroreflex gain

¹Dipartimento di Fisica, Università di Trento, Trento; and ²Dipartimento di Scienze Precliniche Laboratorio Interdisciplinare Tecnologie Avanzate di Vialba, Università di Milano, Milano, Italy

Submitted 15 June 2004 ; accepted in final form 6 December 2004

Although in physiological conditions RR interval and systolic arterial pressure (SAP) are likely to interact in a closed loop, the traditional cross-spectral analysis cannot distinguish feedback (FB) from feedforward (FF) influences. In this study, a causal approach was applied for calculating the coherence from SAP to RR (K_s-r) and from RR to SAP (K_r-s) and the gain and phase of the baroreflex transfer function. The method was applied, compared with the noncausal one, to RR and SAP series taken from 15 healthy young subjects in the supine position and after passive head-up tilt. For the low frequency (0.04–0.15 Hz) spectral component, the enhanced FF coupling (K_r-s = 0.59 ± 0.21, significant in 14 subjects) and the blunted FB coupling (K_s-r = 0.17 ± 0.17, significant in 4 subjects) found at rest indicated the prevalence of nonbaroreflex mechanisms. The tilt maneuver recovered FB influences (K_s-r = 0.47 ± 0.16, significant in 14 subjects), which were stronger than FF interactions (K_s-r = 0.34 ± 0.19, significant in 9 subjects). At the respiratory frequency, the RR-SAP regulation was balanced at rest (K_s-r = 0.30 ± 0.18 and K_r-s = 0.29 ± 0.20, significant in 11 and 8 subjects) and shifted toward FB mechanisms after tilt (K_s-r = 0.35 ± 0.19 and K_r-s = 0.19 ± 0.11, significant in 14 and 8 subjects). The causal baroreflex gain estimates were always lower than the corresponding noncausal values and decreased significantly from rest to tilt in both frequency bands. The tilt-induced increase of the phase lag from SAP to RR suggested a shift from vagal to sympathetic modulation. Thus the importance of nonbaroreflex interactions pointed out the necessity of accounting for causality in the cross-spectral analysis of the interactions between cardiovascular variables in healthy humans.

cross-spectral analysis; coherence and transfer function; cardiovascular regulation; feedback and feedforward mechanisms; nonbaroreflex interactions

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