ECG LEAD-OFF DETECTION USING PHASE SHIFT OF RECOVERED TRANSTHORACIC IMPEDANCE RESPIRATION SIGNAL

A lead-off detector is disclosed for detection of a change of connection state of one or more of the electrical leads which are used to connect a physiological monitoring device, such as an Electrocardiogram ("ECG") monitoring device, with the subject, e.g. patient, being monitored. The disclosed lead-off detector detects such changes rapidly and is not sensitive to electrical noise or thermal fluctuations. For example, the disclosed embodiments may detect disconnection and/or connection of one or more electrical leads and may further detect connection and/or disconnection of one or more electrical leads from the monitoring device, the subject, intervening coupling devices, or a combination thereof. In one embodiment, the disclosed lead-off detector is used in conjunction with a three lead ECG monitor with Transthoracic Impedance Respiration ("TIR") functionality but may also be utilized with other types of physiological monitoring devices. The disclosed lead-off detector measures a phase difference between a signal transmitted to the subject and a signal received therefrom. Wherein the electrical leads are properly connected, the phase difference will be below a defined threshold. However, when one or more of the electrical leads becomes disconnected in some manner, the phase difference between the transmitted signal and the received signal will exceed the threshold. In an alternate embodiment, the clock frequency of the transmitted signal is further compared with the clock frequency of the received signal to detect transitions between the lead connection states and indicate a lead-off event so as avoid noise generated therefrom, referred to as "lead noise", from being further processed.