Detecting loss of full skin contact in patient electrodes

1. A patient electrode adapted to be used with an output device that is configured to emit an alert, comprising:

a pad adapted to be attached onto a skin of a patient;

an electrode lead coupled to the pad; and

a contact detector coupled to the pad, the contact detector being an optical sensor, the optical sensor coupled to the pad so that, when the pad is attached to the skin of the patient normally making full contact with the skin the pad prevents any light from reaching the optical sensor but, if there is loss of full contact between the pad and the skin, the optical sensor is configured to detect illumination from light reaching the optical sensor, the optical sensor adapted to be in one of a plurality of detector states that indicate the detected illumination by the optical sensor, and

in which the output device is configured to emit the alert responsive to a determination from a current one of the detector states that the pad does not contact fully the skin of the patient, the determination being made when the detected illumination changes beyond a threshold.

2. The patient electrode of claim 1 , in which

a sense signal is generated that encodes the current one of the detector states, and

the output device is configured to receive a version of the sense signal.

3. The patient electrode of claim 2 , further comprising:

at least one sense lead configured to transfer the sense signal.

4. The patient electrode of claim 2 , in which the sense signal is wireless.

5. The patient electrode of claim 4 , further comprising:

an RFID tag coupled to the contact detector, and

in which the RFID tag is adapted to be interrogated by an RFID reader, and

the RFID tag backscatters the sense signal responsive to being thus interrogated.