Key to better qualitative diagnostic calibrations in respiratory inductive plethysmography.

Least-squares estimates for coefficients of linear models that predict tidal volume (VT) via respiratory inductive plethysmography (RIP) are given. The qualitative diagnostic calibration sum formula M(RC + KAbd) arises for idealized thoracoabdominal co-ordination within this model-fitting framework. For a normal synchronous breath K is then optimally determined from the ratio of its associated ribcage (RC) and abdomen (Abd) movement standard deviations, not from a ratio that applied to a previously measured breath. M merely rescales relative changes in (RC + KAbd) to absolute changes in VT for correct proportioning. RC and Abd move in complete antipathy during an obstructive apnoea, so use of optimal K ensures (RC + KAbd) tends to zero for such unproductive breathing efforts. The interpretation is extended to more general breathing patterns by using a complementary difference expression M(RC-KAbd) to help identify any antagonistic respiratory actions. The two new constructs are equivalent to the principal components of the combined ribcage and abdomen movements. Together they demonstrate versatile capability in uncalibrated RIP applications for obstructive apnoea detection and tracking relative changes in VT during paradoxical or variable natural breathing. Calibration is appropriate for model-fitting quality assessment but otherwise usually too patient demanding, unnecessary or detrimental to prediction monitoring efficacy.