Calibration of an impedance pneumographl

1 g64.-An experimental calibration of an electrical impedance pneumograph is presented over a range of tidal volumes from 250 to 4,000 ml. Transthoracic impedance measurements were made on four subjects using I-in. cup electrodes, and at a fre-quency of loo kc/set. A ~-ohm change of impedance magni-tude corresponding to an average tidal volume of 830 ml was observed, based on a total of 1,063 measurements. The stand-ard deviation of these data was approximately 507 ~ for low tidal volumes and 307 ~ for the larger tidal volumes. Data from individual subject trials indicated significant variations in the calibration constants and regions of apparent linearity, both between subjects and between trials on each subject. Experi-mental records of the change in impedance magnitude as a function of inspired air volume during inspiration are in-cluded to illustrate typical variations. plethysmography, impedance impedance, transthoracic tidal volume, measurement of respiration meter T HE IMPEDANCE PLETHYSMOGRAPH has been used byanumber of investigators to record changes in the volume of body seg-ments. A variation of the procedure is known to be useful for observing organ volume changes in the thorax (2). Recent publications (I, 3) are evidence of specific interest in the use of electrical impedance measurements to monitor the respiration rate and volume. The principal advantages inherent in a satis-factory impedance pneumograph are the relative small size and weight of the instrument, and the minimum restraint placed on the subject. Original observations on respiratory phenomena recorded by electrical impedance methods are summarized in the litera-ture (I). This report describes a study made of the quantitative relationship between a change in lung volume and a simul-taneously occurring change in transthoracic electrical im-pedance throughout the full range of tidal volume of healthy male subjects. The general objective of the investigation was to establish the value and characteristics of an experimentally calibrated impedance pneumograph for recording tidal air volume