R. Peslin et C. Duvivier, Reliability of thoracic gas volume derived from mechanical impedance at different levels of the vital capacity, RESPIRATION, 66(4), 1999, pp. 323-331
Thoracic gas volume (TGV) may be estimated during spontaneous breathing by
measuring simultaneously respiratory impedance (Zrs) and alveolar gas compr
ession (Vpl) at several oscillation frequencies [Peslin and Duvivier: J App
l Physiol 1998;84:862-867]. Objective: The aim of the study was to test the
validity of that approach at different levels of the vital capacity (VC).
Methods: We measured Zrs and Vpl at frequencies ranging from 6 to 29 Hz in
10 healthy subjects rebreathing BTPS gas in a constant volume body plethysm
ograph, In a first series, the subjects were asked to breathe voluntarily a
t different levels of the VC and oscillation TGV (TGVos) was compared to st
andard plethysmographic TGV (TGVst) assessed immediately after TGVos measur
ements, In a second series, the subjects were asked to change stepwise thei
r lung volume in the middle of the forced oscillation recording, and the ch
anges in TGVos (Delta TGVos) were compared to the changes in lung volume (D
elta V) computed from the integrated flow signal, Results: In most subjects
TGVos and TGVst were highly correlated and the slopes of the relationships
did not differ significantly from unity. Delta TGVos a nd Delta V were a I
so high ly correlated both in individuals and in the group (r = 0,97), and
their signless differences averaged 0.23 +/-: 0.20 liter, Conclusion: We co
nclude that forced oscillation estimates of TGV a re reliable in healthy su
bjects over a large part of the VC.