Journal of Applied Physiology, Vol 58, Issue 2 346-351, Copyright © 1985 by American Physiological Society
Evaluation of phase correction and low gas density to improve thoracic gas volume measurement
P. Begin, R. Peslin, B. Hannhart and C. Gallina
We investigated two methods of decreasing the error on plethysmographic
determinations of thoracic gas volume (TGV) related to cheeks movements
during panting maneuvers: lowering gas density in the airways with an 80%
He-20% O2 mixture and computing TGV from the in-phase component of the
plethysmographic signal (TGVr). The methods were tested by measuring how
TGV estimates varied when panting frequency was raised from 0.8 to 2.5 Hz
during the same occlusion. The measurements were performed in 6 normal
subjects and 12 patients with chronic bronchitis with and without cheeks
support and when the airway was connected to an external device simulating
an increased cheeks compliance. A small negative frequency dependence of
TGV (delta TGV/delta f = -1.2 +/- 0.8%/Hz with cheeks support), most
probably unrelated to upper airway walls, was found in normal subjects.
Delta TGV/delta f was positive and algebraically larger in patients than in
normals, reaching 2.2 +/- 3.4%/Hz without cheeks support and 11.8 +/-
8.0%/Hz with the additional cheeks. The latter value was only 20% smaller
when computed on the basis of TGVr, demonstrating the limited usefulness of
the phase-based correction. In contrast, breathing He-O2 decreased delta
TGV/delta f to approximately 50% of its air value (P less than 0.01) and
appears as an effective way to diminish the error in obstructive patients.
