An analogue instrument for the measurement of respiratory impedance using the forced oscillation technique

The successful development of non-invasive assisted ventilation via a nasal mask has led to the requirement for improved methods of monitoring the res piratory system. Measurements of respiratory impedance during assisted vent ilation using acoustic methods are showing considerable promise in providin g this clinical data. The method involves imposing very low amplitude acoustic oscillations onto the spontaneous or assisted respiratory airflow. The subsequent interaction with the respiratory system modifies the pressure and Row relationship of the Forced oscillations. The ratio of pressure to now can be used to measur e in real time the absolute value of respiratory input impedance. As a resu lt a versatile, non-invasive and repeatable profile of respiratory mechanic s is obtained. Using a 5 Hz conventional forced oscillation frequency, data highly sensitive to airflow obstruction and capable of tracking. mechanica l events and responses become available to the clinician. Recent studies wi th ventilated and sleeping subjects confirm future potential for the forced oscillation technique in vivo. We describe an instrument named the respiratory impedance monitor (5 Hz), w hich utilizes the forced oscillation technique (FOT). This fully developed device is designed in accordance with agreed international clinical guideli nes. Comparative clinical data from normal subjects and patients with chron ic obstructive pulmonary disease is presented.