Apparatus for analyzing chest motion during application of cardiopulmonary resuscitation (=CPR), the apparatus comprising: means configured to detect ECG signals during application of chest compressions; a motion sensor configured to be positioned to sense information on motion of the chest, the motion sensor comprising a conductor and a magnet configured to sense motion by sensing current induced in the conductor by relative motion between the conductor and the magnet; and means configured to detect the output of the motion sensor from which information on motion of the chest is determined. Provided are also means configured to use the information on motion to reduce at least one signal artifact in the ECG signal resulting from the chest compressions.