The baroreflex contribution to spontaneous heart rhythm assessed with a mathematical model in rats Chiara Berteotti a , Carlo Franzini a , Pierluigi Lenzi a , Elisa Magosso b , Mauro Ursino b , Giovanna Zoccoli a , Alessandro Silvani a, ⁎ a Department of Human and General Physiology, University of Bologna, Italy b Department of Computer Science, Informatics and Systems, University of Bologna, Italy Received 28 May 2007; received in revised form 3 August 2007; accepted 4 September 2007 Abstract In Spontaneously Hypertensive (SHR) and Wistar–Kyoto (WKY) normotensive rats, we quantified the extent to which spontaneous fluctuations of heart period (HP) may be determined from arterial pressure based on linear baroreflex properties. We analyzed time series (30-s length) of low-frequency (b 0.8 Hz) fluctuations of HP and mean arterial pressure obtained during quiet wakefulness, rapid-eye-movement sleep (REMS) and non-rapid-eye-movement sleep (NREMS) as well as a control set of surrogate isospectral data with random phase. HP was modeled as the summed output of two parallel linear transfer functions with arterial pressure as input. The mean square difference between modeled and recorded HP was minimized by varying model parameters. The percentage of time series, in which such difference was lower than half the measured HP variance was significantly lower in REMS (6 ± 1%, SHR; 5 ± 1%, WKY) than either in quiet wakefulness (25 ± 2%, SHR; 35 ± 3%, WKY) or NREMS (33 ± 3%, SHR; 27 ± 3%, WKY), and in quiet wakefulness, it was significantly lower in SHR than in WKY. In surrogate data, these percentages were significantly lower than in recorded data during quiet wakefulness and NREMS, but not during REMS. The extent to which linear baroreflex properties explain spontaneous heart rhythm thus depends on the interaction between the behavioral state and the hypertensive disease, and in REMS, may be accounted for by chance couplings between HP and arterial pressure. © 2007 Elsevier B.V. All rights reserved. Keywords: Baroreceptor reflex; Heart; Hypertension; Mathematical models; Sleep 1. Introduction Linear techniques have been widely applied to estimate cardiac baroreflex sensitivity from the spontaneous fluctua- tions of heart period (HP) and arterial pressure (Robbe et al., 1987; Bertinieri et al., 1988; Laude et al., 2004). These techniques analyze the linear component of the influence, which the arterial pressure fluctuations exert on HP through the baroreflex. The assessment of such component and of its changes in physiological and pathological conditions is an active area of research (Di Rienzo et al., 2001; Johansson et al., 2005; Nollo et al., 2005). Nonetheless, the extent to which heart rhythm is determined by the baroreflex has never been quantified during sleep, when wide changes in brain activity (Franzini, 1992; Maquet, 2000) may alter the central integration that produces cardiac autonomic outflow. By analyzing the linear cross-correlation function be- tween HP and arterial pressure, Berteotti et al. (2007) recently found that the differences between Spontaneously Hypertensive Rats (SHR) and their normotensive Wistar– Kyoto (WKY) controls depend on the wake–sleep state. These results led to the hypotheses that the baroreflex contribution to HP control is negligible during rapid-eye- movement sleep (REMS) in both strains and lower in SHR Autonomic Neuroscience: Basic and Clinical 138 (2008) 24 – 30 www.elsevier.com/locate/autneu ⁎ Corresponding author. Dipartimento di Fisiologia Umana e Generale, Università di Bologna, Piazza di Porta San Donato, 2, 40126 Bologna, Italy. Tel.: +39 051 2091739; fax: +39 051 2091737. E-mail address: alessandro.silvani3@unibo.it (A. Silvani). 1566-0702/$ - see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.autneu.2007.09.003