The effect of breath size and posture on calibration of the respiratory inductive plethysmograph by multiple linear regression

Abstract

The accuracy of the respiratory inductive plethysmograph (Respitrace) for estimation of lung volume changes during quiet breathing and vital capacity (VC) manoeuvres was evaluated using a variant of the multiple linear regression (MLR) technique. We applied this technique successively on quiet breathing, on the whole VC, and on each of the four quarters of the VC separately. This was carried out in six body positions. The best estimation of tidal volumes was obtained when calibration factors calculated during quiet breathing were used. The best estimation of VC was obtained when the calibration factors were adapted to the level of lung inflation. These results indicate that, using a single position MLR calibration method, the Respitrace measures tidal and VC mouth volumes very accurately. The accuracy of this MLR method for estimation of the rib cage and abdominal contributions was validated by comparison with isovolume calibration factors. Both techniques gave very similar results during tidal breathing. However, the MLR calibration factors may have no physiological meaning (i.e. for volume partitioning) when they are calculated from VC manoeuvres, in which more than two degrees of freedom are involved.

Comparative analysis of the isovolume calibration method for non-invasive respiratory monitoring techniques based on area transduction versus circumference transduction using the connected cylinders model

“…It was demonstrated that, either by fixing the height or constraining it to vary in a well-defined way with changes in the radius, under reasonable assumptions, the error in the inference of the volume introduced by neglecting these variations in height generally amounted to no more than 2.5%. It was also demonstrated that, in principle, the calibration coefficients for each of the two channels noted above derived from the isovolume technique will depend on the initial volume of the compartments, often determined by posture, a fact borne out by measurement (Raza 1997, Verschakelen et al 1989.…”