Abstract
A new inductive plethysmograph has been developed for non-invasive respiratory monitoring. This device consists of two coils of insulated wire sewn onto elastic bondages that encircle the rib cage and abdomen, and electronic circuits for detecting the deviation of the oscillation frequency caused by the change in the length of the coils. The deviation is nearly proportional to tidal volume, and is converted into voltage change by phase locked loop. The static accuracy of the device is tested by comparing its output with that of a hot wire flowmeter. The difference between the two outputs is within ±10% for normal respiration, but the output of the device shows saturation when tidal volume exceeds 2l. The movement of the body does not have much effect on the accuracy.
