Contactless recording of cardiac related thoracic conductivity changes

Cardiac related changes in the electrical conductivity distribution of the thorax were recorded in real-time with an electromagnetic sensor consisting of a 3.5 cm radius coil, a 4 MHz oscillator and an active RF voltmeter. Operation of the sensor is based on measuring changes in the amplitude of a marginal RF oscillator, caused by eddy current losses in the heart region. Signals recorded from 6 normal subjects in multiple sessions (1 hour to 1 month) showed good repeatability. The average SNR for signals recorded with the coil placed over the sternum was 34 dB. A possible application of this type of sensor is for non-invasive continuous assessment of left ventricular ejection fraction.