To estimate the transfer impedance of the respiratory system \documentclass[12pt]{minimal}
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$$\left( {Z_{{\text{tr}}} } \right)$$
\end{document} we applied pressure forcing at the mouth from 1 to 24 Hz in eight healthy subjects and used optoelectronic plethysmography (OEP) to measure volume changes of the chest wall and its different compartments: pulmonary rib cage \documentclass[12pt]{minimal}
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$$\left( {RC_p } \right)$$
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$$\left( {RC_a } \right)$$
\end{document} and abdomen (AB). Spectral analysis allowed assessment of input impedance \documentclass[12pt]{minimal}
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$$\left( {Z_{{\text{in}}} } \right)$$
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$${Z_{{\text{RC}}_{\text{p}} } ,}$$
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$${Z_{{\text{AB}}} }$$
\end{document} transfer impedances. As expected, averaged values of \documentclass[12pt]{minimal}
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$${Z_{{\text{RC}}_p }, }$$
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$${Z_{{\text{RC}}_a } ,}$$
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$${Z_{AB} }$$
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\end{document} were, respectively, 35.3±1.4SD, 13.8±1.4, and 50.8±2.8 at low frequencies (<8 Hz) and 63.1±5.5, 20.7±5.2, and 16.2±2.3 at higher frequencies (>10 Hz). The validation of our approach was based on the comparison with a physical model comprised of a rubber membrane stretched over and attached to the lip of a bowl. We conclude that the combination of forced oscillations with OEP provides the simultaneous assessment of \documentclass[12pt]{minimal}
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$${Z_{in} }$$
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$${Z_{tr} ,}$$
\end{document} it does not require the use of a plethysmographic chamber and it allows the separation between the different rib cage-abdominal pathways. © 2001 Biomedical Engineering Society.
