Non-invasive ventilatory volume monitor

Continuous ventilatory volume monitoring for a long period is indispensable to the treatment and nursing of critically ill patients, so that the non-invasive electrical impedance method was considered to see if it could take the place of a conventional method, such as pneumotachography. This report is composed of the following parts: (a) basic studies concerned with several factors which influence the accuracy, stability and reproducibility of the method, (b) development of impedance ventilatory volume monitor based on above mentioned basic studies and (c) clinical results obtained with the newly developed monitor. The monitor can measure tidal volume, breath by breath, continuously within about plus and minus 10% accuracy. It memorises a calibrated correlation curve for the conversion of impedance changes into tidal volumes by a microprocessor. As long as no abnormal physiological event occurs in the thoracic space, this accuracy is maintainable with calibrations only once or twice per day.