Spectral and symbolic analysis of Heart Rate data during Tilt Test Camillo Cammarota * Enrico Rogora † Abstract Spectral analysis of heart rate sequences is commonly used to inves- tigate neuroauthonomic control of heart rate by means of two indexes, the low and the high frequency power. For tilt test data of normal sub- jects we compare the spectral indexes with new indexes defined within the framework of symbolic analysis. We define two classes of binary words of length 4: the first class is related to “acceleration” of heart rate and the second class to “stationary behavior”. The new indexes measure the change in frequency of the two classes before and after the tilt. Data analysis of 13 normal subjects shows that the behavior of the new indexes is in agreement with that of spectral ones. PACS 2006: 87.19.Hh 1 Introduction Head Up Tilt (HUT) test can be used to evaluate how human body regulates blood pressure and heart rhythm in response to some very simple stresses. The HUT test analyzed in this paper consists of monitoring patients in two different conditions. First the patient remains in a supine position for twenty minutes; then, after the supine heart rate and blood pressure are obtained, the patient is tilted using a motorized table with a foot-board and remains in inclined position for other twenty minutes. During this test an electro- cardiogram (ECG) is performed and blood pressure is measured. The tilt is believed to produce changes in the neuroauthonomic controls consisting in an increment of the sympathetic activity and a decrease of the parasympathetic (vagal) activity. These controls can be studied by using the RR sequence, * Dept. of Mathematics, University of Rome ”La Sapienza”, cammar@mat.uniroma1.it † Dept. of Mathematics, University of Rome ”La Sapienza”, rogora@mat.uniroma1.it 1