Available online at www.sciencedirect.com Physica A 327 (2003) 168–173 www.elsevier.com/locate/physa Model for the heart beat-to-beat time series during meditation A. Capurro a; c , L. Diambra b , C.P. Malta a ; ∗ a Instituto de F sica, Universidade de S˜ ao Paulo, Rua do Mat˜ ao Travessa R 187, CEP 05508-900 S˜ ao Paulo, SP, Brazil b Instituto de Ciˆ encias Biom edicas, Universidade de S˜ ao Paulo, Av. Lineu Prestes 1524, CEP 05508-900 S˜ ao Paulo, SP, Brazil c Departamento de Neurosiologia, Instituto de Investigaciones Biol ogicas Clemente Estable, Avenida Italia 3318, Montevideo 11600, Uruguay Abstract We present a model for the respiratory modulation of the heart beat-to-beat interval series. The model consists of a pacemaker, that simulates the membrane potential of the sinoatrial node, modulated by a periodic input signal plus correlated noise that simulates the respiratory input. The model was used to assess the waveshape of the respiratory signals needed to reproduce in the phase space the trajectory of experimental heart beat-to-beat interval data. The data sets were recorded during meditation practices of the Chi and Kundalini Yoga techniques. Our study indicates that in the rst case the respiratory signal has the shape of a smoothed square wave, and in the second case it has the shape of a smoothed triangular wave. c  2003 Elsevier B.V. All rights reserved. PACS: 87.17.Aa; 87.19.Hh; 05.45.-a Keywords: Pacemaker; Heart rate variability; Respiratory modulation; Meditation 1. Introduction The normal respiratory cycle is accompanied by changes in autonomic tone that modulates the heart rate. The activity of the vagal nerve endings increases during exhalation, and the activity of sympathetic bers increases during inhalation, causing the “respiratory modulation” (RM) or “sinus arrhythmia”, i.e., during inhalation the * Corresponding author. Fax: +55-11-3814-0503. E-mail address: coraci@if.usp.br (C.P. Malta). 0378-4371/03/$ - see front matter c  2003 Elsevier B.V. All rights reserved. doi:10.1016/S0378-4371(03)00471-0