Wearable transducer to monitor respiration in a wireless way

Conductive rubber belt with electrical resistance changed by lengthening was incorporated within the patient´s pants, which operated as a waist band transducer. The resistance changes induced by the abdominal dimension variation during breathing were converted into a voltage signal by a bridge circuit, then digitized followed by wireless transmission with zigbee protocol. The wireless transmission module was implemented small enough to carry conveniently in pocket. The wireless receiver module was also made to forward the signal to a local computer station through RS232 serial communication port, where respiration was monitored. CO₂ inhalation experiments were performed in 4 normal men to evaluate measurement accuracy in the tidal volume(V_T). 0~5% CO₂ inhalation for a few minutes increased V_T upto approximately twice in steady state with corresponding increase in the abdominal signal. Customized calibration by CO₂ inhalation experiment for each subject resulted a mean relative error of 8% perhaps acceptable for general monitoring purposes. The present results enable wireless remote monitoring of respiration, thus could be applied to a ubiquitous health care system.