Ballistocardiographic Spectrum Studies with a Tilt Table J. Alametsä 1,2 , J. Viik 1 , A. Palomäki 2 1 Tampere University of Technology, Department of Biomedical Engineering, Tampere, Finland 2 Kanta-Häme Central Hospital, Hämeenlinna, Finland Abstract— The purpose of this preliminary work is to study the effect of a tilt table test procedure on ballistocardio- graphic (BCG) signal by using Electromechanical Film (EMFi) sensors. The ECG, BCG, carotid pulse (CP) from the neck near the carotid artery and ankle pulse signals were recorded from 7 persons. The spectral and temporal components of the recordings during the tilt table test were studied. The spectral and temporal properties of BCG signal changed due to the tilt test, change in amplitude levels of the systolic BCG components and in spectral domain. Blood pressure values and pulse changed due to the tilt test. This was also seen in the changed aortic pulse wave velocity (PWV) values. According to this study, BCG measurements combined with a tilt test can be used as a very simple non- invasive method in hemodynamic studies. Keywords— EMFi, BCG, tilt test I. INTRODUCTION Ballistocardiography (BCG) is a non-invasive method for cardiac and respiratory evaluation and it reflects closely the strength of myocardial contraction revealing the condition of the heart [1]. It is a record of the move- ments of the body caused by shifts in the centre of the mass of blood, and to a lesser extent, of the heart, caused by cardiac contraction [1]. When the heart pumps blood from atrium via ventricles to the ascending aorta, recoil of opposite direction is applied to the body and its force and direction is changes according to the cardiac cycle. The BCG waveforms (Fig. 1) have been divided into three groups, labelled with letters; systolic part consists of pre- ejection (FGH) and ejection (IJK) of the heart cycle and the diastolic part (LMNO) [1]. Fourier analysis has been used earlier in BCG analysis when the elastic properties of the blood vessels and the dynamics of the human body on the BCG have been studied [2, 3]. In this paper a newer version of the Mobile Physio- logical Signal Measurement Station [4] has been used for recording of BCG and carotid pulse signals with EMFi sensors. The main goal of this study is to evaluate spectral and temporal differences in measured signals induced by the tilt table test. II. METHODS A tilt table test is often used to identify patients who have a vasodepressor and/or cardioinhibitory response as a cause of syncope. Patients are positioned on a tilt table in the supine position and are tilted upright to a maximum of 60 to 80 degrees for 20 minutes or more [5]. Patients with symptoms of dizziness or lightheadedness, with or without a loss of consciousness (fainting), suspected to be associated with a drop in blood pressure or positional tachycardia have been usually tested. 20 20.5 21 21.5 22 -5 -4 -3 -2 -1 0 1 2 Unfiltered signal Amplitude Time (s) Aortic valve open Aortic valve shut Ventricular systole; mitral valve closed Ventricular diastole Aortic valve opens Mitral valve closes Aortic valve closes Mitral valve opens Atrial systole 1. Heart sound 2. Heart sound H I J K L M N O G F P T D DW Fig. 1 Signals recorded in the sitting position; suppressed respiration and case 1. Signals from the bottom to top: PCG (heart sound), ECG, BCG signal from the EMFi sensor on a chair and from the carotid artery recorded with EMFi sensor strip. The typical heart cycle lasts around 0.8s. The EMFi [6] sensor is basically a thin biaxially ori- ented plastic film coated with electrically conductive lay- ers which are permanently polarized. Changes in the pres- sure acting on the film generate a charge on its electri- cally conductive surfaces and this charge can be meas- ured as a current or a voltage signal. It can convert me- chanical energy to electrical energy and vice versa. Thus the EMFi acts as a sensitive movement sensor suitable for BCG recordings. Signals from the EMFi sensors were recorded with the newer version of the Mobile Physiological Signal Meas- urement Station [4] into a notebook computer with a data acquisition card (Daqcard 6036E) and the recordings were transcribed to ASCII format. In the Mobile Physio- logical Signal Measurement Station an active Butterworth 8. degree low pass filter was used, having the 256 Hz cut- off frequency. The Fourier analysis of the BCG was used to evaluate the state and operation of the heart and the elastic properties of the blood vessels due to hemody- namic changes induced by the body position. III. MEASUREMENTS AND STUDY POPULATION The recordings were made with a tilt table, where the big EMFi sensor (180 x 60 cm) was beneath the measured person. Two EMFi sensor strips (10 x 2 cm) were at- tached to the neck near carotid arteries and similar EMFi sensor strips were attached to the wrists and ankles (dor- salis pedis pulse) in order to study time domain properties of the measured pulse signals. In order to assess artery O. Dössel and . ( Eds.): WC 2009,I FMBE Proceedings 25/IV, pp. www.springerlink.com W C. Schlegel 1561–1564, 2009.