Mathematical Medicine and Biology Advance Access first published online on April 30, 2008
This version published online on May 1, 2008
Mathematical Medicine and Biology, doi:10.1093/imammb/dqn005
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Analysis of extrema of heartbeat time series in exercise test

Department of Mathematics, University of Rome "La Sapienza" P. le A. Moro 5, 00185 Roma

Department of Clinical Sciences, University of Rome "La Sapienza", Viale del Policlinico 155, 00161 Roma
Email: cammar{at}mat.uniroma1.it
Email: mario.curione{at}uniroma1.it
Received on June 27, 2007. Revised on September 26, 2007. Accepted on January 29, 2008.
The heartbeat time series of the electrocardiogram recorded during exercise test clearly reflects the physiological control mechanism of the autonomic nervous system on heart rate. This series shows both decreasing and increasing trends and variability of the variance. We analyse the series of intervals between two consecutive extrema, i.e. the durations of accelerations or decelerations of heart rate. We compute the distribution of the length of these intervals and their mean in a model of stationary independent variables, where they are independent of the variables distribution. We use the mean length as discriminant statistics to compare stress and recovery phases. Data analysis performed over the heartbeat series of 14 healthy subjects shows significant difference between stress and recovery.
Keywords: exercise test; extrema; heartbeat; time series; RR interval