Interest and limitations of the respiratory acoustical impedance

The dynamic relationship between pressure and air flow at the mouth is usually described by the frequency dependence of the respiratory acoustical impedance (RAI). The RAI can be measured up to several hundred hertz by the use of forced excitation techniques. The RAI critically depends on the simplifications made in the characterization of the response of the respiratory system. In particular, the limitation of the frequency interval occasions a loss of information. Nonlinearities and nonstationarities are factors limiting the significance of the RAI. Another source of errors and variability for the RAI is the presence of the upper airway shunt. Technical and conceptual improvements in the measurements of the RAI in connection with clinical studies of asthma and vascular congestion are presented.<>