Qualitative diagnostic calibration (QDC)
Overview
QDC is a methode to calibrate the sum of the AB- and RC signal, see [Sackner1989] and [Groote2001]. The calibrated sum signal is needed to calculate the tidal volume Vt, voluntarychanges of the Vt amplitude and the FRC signal.
Details
The QDC calibration methode consists in deriving a proportionality constant K between the AB- and the RC signal. This methode is based on the equations of the isovolume maneuver calibration (ISOCAL) and is done in two steps.1) correct proportioning of the AB- and RC electrical gains
2) proportioning the subject breaths to an external volumetric device e.g., a SP or integrated PNT system to attain equivalency
Calibration process
Natural breathing measurements with a constant tidal volume (Vt) over a 5 min period are required for calibration. In this case K is about the ratio of the standard deviations (std) of the uncalibrated changes (delta u) of AB to RC volume deflections.
K can be interpreted geometrically as the absolute value of the slope of the line defined by the set of uncalibrated volumes or the respective regression line.
Implementation in the RIP app
The factor K can be set manually or can be determined automatically, based on the QDC method, see "Calibrate RIP signals by applying quantitative diagnostic calibration (QDC)".
The automatic calibration can only be used when the number of INSP and EXP are equal in RIP RC, RIP AB and RIP AB+RC, and the first breath in each signal is corresponding to each other.
The applied method consists in three steps.
1. determine mean SUM and standard deviation of uncalibrated SUM (AB+RC)
2. exclude breaths with large deviations, meaning exclusion of breaths > or < than 1std from the mean SUM
3. determine the calibration factor by determining std(delta AB) and std(delta RC) of valid breaths and the ratio of the standard deviations