Electrostatic Interference in Contactless Biopotential Measurements

Sensing biopotentials without contacting the subject's body could obviate skin preparation and allow the recording of the ECG without needing to remove clothing. However, body surface charges unrelated to bioelectric signals can interfere the record by contributing a signal that results from the distance variation between the body surface and the electrode used to detect electric potential. This paper shows that, for ungrounded human subjects, distance changes related to the impact of the heart on the thorax can yield electric potentials higher than those related to the ECG. Therefore, we dispute that non-contact biopotentials recordings obtained without any control of electrostatic charges can be attributed only to the ECG. Because earth grounding a patient is forbidden by electrical safety regulations, non-contact biopotential measurements ask for control measures to prevent the generation and accumulation of electrostatic charges, the same as conventional measurements.