Single-position calibration of the respiratory inductance plethysmograph

Since we intended to use the respiratory inductance plethysmograph (RIP) to study breathing patterns in a single body position, we developed a method to calibrate the RIP in one position (seated) and verified the stability of this calibration procedure during a 60-min period. The subject breathed spontaneously through a pneumotachograph for 1 min during all calibration and verification runs. All inspiratory data from the abdomen and rib cage RIP transducers was analyzed using multiple linear regression analysis to calculate calibration factors for the transducers. Eight normal subjects were studied, and the stability of calibration at 20, 40, and 60 min was determined. The correlation coefficients were all greater than 0.94. The mean slope and mean intercept describing the relationship of the RIP volume to the pneumotachograph volume for all calibration and verification runs were 0.995 +/- 0.074 and 0.012 +/- 0.018 liter, respectively. This calibration method allows a spirogram to be generated from the RIP signals. Therefore, this technique may be valuable in further investigating resting breathing patterns in humans.