Comparison of time and frequency domain methods for the feedback on chest compression rate

During cardiopulmonary resuscitation feedback systems can help rescuers to achieve optimal chest compression rates. In this paper we describe and compare two methods to provide chest compression rate feedback based only on the thoracic impedance signal, available in automatic external defibrillators. The first method (time domain) identified the relative maxima of the impedance and characterized each fluctuation by features of amplitude and duration to classify them as compression or non-compression. Then it reported the chest compression rate as the median of the rates of the previous compressions. The frequency domain method computed the Fast Fourier Transform for short windows of the impedance and identified the highest peak in a frequency band. If its amplitude exceeded a dynamic threshold, its frequency was reported as the compression rate. Both methods provided global root mean square errors of the estimated rate below 3.2 min^-1 when evaluated with out of hospital cardiac arrest records.