Patent US 4,433,693

A method and assembly for monitoring respiration and detecting apnea. The assembly includes an oscillator for generating an electromagnetic field having an output frequency in the radio frequency range and a high Q passively tuned LC circuit which has a resonant frequency variable in the radio frequency range generated by the oscillator. The LC circuit responds to the electromagnetic field by absorbing electromagnetic energy from the field when the resonant frequency matches the output frequency of the oscillator. A band is positioned about the subject's chest or abdominal cavity to vary the resonant frequency of the LC circuit in response to the expansion and contraction of the subject's chest or abdominal cavity. A detecting means is also provided for detecting when the LC circuit is responsive to the electromagnetic field established by the oscillator. In one embodiment the output frequency of the electromagnetic field established by the oscillator is maintained constant and the detecting means includes reset timing means for providing a signal when the LC circuit fails to respond to the electromagnetic field within a predetermined time period. In a second embodiment the output frequency of the electromagnetic field established by the oscillator is varied within the predetermined frequency range and the detecting means includes reset timing means for providing a signal when the LC circuit fails to respond to the electromagnetic field at different resonant frequencies within the predetermined frequency range within a predetermined time period.