Respiratory input impedance measurement: forced oscillation methods

The paper reviews how forced oscillation techniques (FOT) for measuring respiratory input impedance Z(rs,in) have recently been used in clinical applications. Z(rs,in) is clinically relevant, as it provides data on both the resistive, R-rs, and nonresistive, X-rs, components of the respiratory system. Additionally, when excitatory test signals extending into low- (<4 Hz) or high-frequency (> 100 Hz) ranges are used, reliable partitioning of lung tissue from airway components is feasible. Adult and paediatric studies examining the use of Z(rs,in) for routine lung-function assessment, sleep and mechanical ventilation are reviewed. For clinicians, Z(rs,in) is repeatable and sensitive to airway resistance. It is helpful for assessing unco-operative and severely obstructed patients, for monitoring mechanics during artificial ventilation and for tracking airway closure during sleep studies. For paediatricians, longitudinal studies of the growth and development of the respiratory system can also be made using Z(rs,in). Forced oscillation techniques, however, require further standardisation, and Z(rs,in) is limited by upper-airway shunt artifacts. In conclusion, measurement of Z(rs,in) using FOT is an important and sophisticated non-invasive lung-function test, showing good potential for future clinical applications.