Cardiac Output Measurement Using Ballistocardiogram

Abstract

Ballistocardiogram (BCG) is a non-invasive technique to measure cardiac parameters. It was popularized by Dr. Isaac Staar in 1940. The Ballistocardiogram signal is generated due to the vibrational activity of the heart. BCG was considered as a promising technique but was replaced by Electrocardiogram due to the difficulty involved in detecting and analysing the BCG waveforms. With the increase in processing power and better signal processing techniques over the last few decades, BCG has regained its prominence and is being considered to be used as a continuous patient monitoring system. The usability of BCG was limited in the earlier days due to the large size of the equipment and the lack of signal processing systems to analyse this complicated signal. Cardiac output is defined as the amount of blood pumped out by the heart in a minute. This parameter can be utilized to determine the state of the heart. One method to determine the cardiac output from BCG waveform has been discussed in section II of this paper. The sensor used for our experiment is a lightweight and flexible sheet type electromechanical film which is placed on the seat of the chair. The setup used has a two-stage amplifier which is connected to a data acquisition card which is in turn connected to a laptop. The signal processing is done using NI’s software LabView. The BCG setup was made and the signal was successfully validated with ECG. The R-J interval, which is the interval between the R peak of the ECG signal and J peak of the BCG signal, was determined. Echocardiogram, another cardiac measurement instrument, was kept as a standard basis for determining the cardiac output from the BCG signal. Recording of 14 different subjects have been taken and the cardiac output has been determined for each case.