Evaluation of differential linear transformers as a non-invasive ventilatory method in supine subjects

We present a new method to measure thoraco-abdominal perimeter variations using differential linear transformers inserted in belts. The high sensitivity (250 mV/mm), the low time drift (1 mV/24 h compared to a 1 V output for a tidal volume), the good frequency response (up to 10 Hz) and low cost (12,000 FF) are the major advantages over other devices. After calibration (using change contribution of thorax and abdomen and the least square method for calculation of volume-motion coefficients), estimated tidal volumes in 23 adults in supine position are within 0.06 +/- 5.17% and changes in functional residual capacity (43-453 ml) are within 3.4 +/- 15.3% when compared with direct spirometry. These results show that the method can be used to monitor ventilation accurately in supine healthy subjects.